Bark Ash to Improve Phosphorus Availability in Acidic Soils

agronomy

Article Optimisation of Charcoal and Sago (Metroxylon sagu) Bark Ash to Improve Phosphorus Availability in Acidic Soils

Prisca Divra Johan 1, Osumanu Haruna Ahmed 1,2,3,*, Ali Maru 4, Latifah Omar 1,2 and Nur Aainaa Hasbullah 5

1 Department of Crop Science, Faculty of Agricultural Science and Forestry, Bintulu Sarawak Campus, Universiti Putra Malaysia, Bintulu 97008, Malaysia; [email protected] (P.D.J.); [email protected] (L.O.) 2 Institute Ekosains Borneo (IEB), Faculty of Agriculture and Forestry Sciences, Bintulu Sarawak Campus, Universiti Putra Malaysia, Bintulu 97008, Malaysia 3 Institute of Tropical Agriculture, Universiti Putra Malaysia (ITAFoS), Seri Kembangan 43000, Malaysia 4 School of Agriculture, SIREC, CBAS, University of Ghana, Legon, Accra 23321, Ghana; [email protected] 5 Faculty of Sustainable Agriculture, Sandakan Campus, Universiti Malaysia Sabah, Sandakan 90509, Malaysia; [email protected] * Correspondence: [email protected]; Tel.: +60-19-3695095

Abstract: Soil acidity is an important soil factor affecting crop growth and development. This ultimately limits crop productivity and the profitability of farmers. Soil acidity increases the toxicity of Al, Fe, H, and Mn. The abundance of Al and Fe ions in weathered soils has been implicated in P fixation. To date, limited research has attempted to unravel the use of charcoal with the incorporation of sago (Metroxylon sagu) bark ash to reduce P fixation. Therefore, an incubation study was conducted in the Soil Science Laboratory of Universiti Putra Malaysia Bintulu Sarawak Campus, Malaysia for 90 days to determine the optimum amounts of charcoal and sago bark ash that could be used to improve the P availability of a mineral acidic soil. Charcoal and sago bark ash rates varied by 25%, whereas Egypt rock phosphate (ERP) rate was fixed at 100% of the recommendation rate. Citation: Johan, P.D.; Ahmed, O.H.; Soil available P was determined using the Mehlich 1 method, soil total P was extracted using the Maru, A.; Omar, L.; Hasbullah, N.A. aqua regia method, and inorganic P was fractionated using the sequential extraction method based Optimisation of Charcoal and Sago on its relative solubility. Other selected soil chemical properties were determined using standard (Metroxylon sagu) Bark Ash to procedures. The results reveal that co-application of charcoal, regardless of rate, substantially Improve Phosphorus Availability in increased soil total carbon. In addition, application of 75% sago bark ash increased soil pH and at the Acidic Soils. Agronomy 2021, 11, 1803. 3+ 2+ https://doi.org/10.3390/ same time, it reduced exchangeable acidity, Al , and Fe . Additionally, amending acidic soils with agronomy11091803 both charcoal and sago bark ash positively enhanced the availability of K, Ca, Mg, and Na. Although there was no significant improvement in soil Mehlich-P with or without charcoal and sago bark Received: 29 April 2021 ash, the application of these amendments altered inorganic P fractions in the soil. Calcium-bound Accepted: 3 June 2021 phosphorus was more pronounced compared with Al-P and Fe-P for the soil with ERP, charcoal, and Published: 8 September 2021 sago bark ash. The findings of this study suggest that as soil pH decreases, P fixation by Al and Fe can be minimised using charcoal and sago bark ash. This is because of the alkalinity of sago bark ash Publisher’s Note: MDPI stays neutral and the high affinity of charcoal for Al and Fe ions to impede Al and Fe hydrolysis to produce more with regard to jurisdictional claims in H+. Thus, the optimum rates of charcoal and sago bark ash to increase P availability are 75% sago published maps and institutional affil- bark ash with 75%, 50%, and 25% charcoal because these rates significantly reduced soil exchangeable iations. acidity, Al3+, and Fe2+.

Keywords: phosphorus ﬁxation; inorganic phosphorus speciation; waste management; liming materials; carbon; functional groups; organic acids Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and 1. Introduction conditions of the Creative Commons Attribution (CC BY) license (https:// Phosphorus is an essential nutrient which serves as a component of many key plant creativecommons.org/licenses/by/ structural compounds and as a catalyst in the conversion of numerous biochemical re- 4.0/). actions in plants. It induces the development of reproductive organs in plants, pro-

Agronomy 2021, 11, 1803. https://doi.org/10.3390/agronomy11091803 https://www.mdpi.com/journal/agronomy Agronomy 2021, 11, 1803 2 of 28

motes root growth, and enhances crop quality and maturation through accretion, transfer, and release of energy in several cellular metabolic processes during degradation and biosynthesis [1–3]. Phosphorus availability is limited in soils, especially in acidic soils such as highly weathered ultisols and oxisols. This limitation is mainly because of the abundance of Al and Fe resulting from high weathering of the soils’ minerals [4,5]. These acidic cations tend to convert P in the soil solution to water-insoluble Fe-P and Al-P. These water insoluble Fe-P and Al-P compounds are not readily available for plant uptake [6,7]. Orthophosphates in soil solution react with Fe and Al species to form amorphous Fe-P and Al-P compounds, and these reactions can decrease P availability [8,9]. Phosphorus is mostly accessible to plants at a soil pH of between slightly acidic and neutral (6.5 to 7) [10,11]. The total soil P content usually ranges from 50 to 3000 mg kg−1 (existing in organic and inorganic forms). However, only a small proportion of the total P (usually <1%) is available for plant uptake [10,12]. This is because in acidic soils, P is fixed by the active forms of Al and Fe oxides and hydroxides, whereas in alkaline soils, P reacts with Ca to form insoluble phosphate compounds [13,14]. As a solution for P fixation, farmers tend to apply a large amount of P fertilisers to saturate the capacity of P sorption and to also ensure that there is sufficient available P for plant uptake [15]. Excessive use of P fertilisers is not only uneconomical, but it also has adverse effects on the environment. First, P fertilisers are largely derived from rock phosphate, which is a non-renewable resource and major deposits are only found in a few countries [16,17]. Second, applications of P fertilisers to soils with high P sorption capacity can be inefficient because P largely accumulates in the soil in sparingly soluble forms [18]. Third, when soils are saturated with P, the excess P has a greater potential to enter water bodies through soil erosion [19], surface runoff, and leaching [20]. The losses of P through these processes lead to eutrophication and water quality deterioration [21,22]. To this end, studies have been conducted to improve P availability using lime [23–25]. Liming is the conventional method to improve soil pH so as to solubilise Al and Fe to release fixed P[26,27]. However, liming is an expensive soil conditioning approach because it is not practical for farmers to apply higher rates of lime frequently. Furthermore, over-liming causes calcium phosphate formation [28], a reaction which also causes P to be fixed or makes P unavailable for optimum plant use. In developing countries, the forestry and agricultural sectors play important roles in their socio-economic development. This has resulted in the exponential production of wood residues. As an example, the Malaysian timber industry generates approximately 3.4 million m3 of annual wood residues, such as sawdust, wood chips, bark, slab, and other raw materials, with a standard 55% recovery rate [29]. Approximately 43% of the total tree volume remains in the forest during logging operations, 13% of the sawdust is produced in the sawmill industry and 53% of the logs are discarded as waste during processing into plywood [30]. Therefore, the timber industry typically converts these wastes into charcoal, briquettes, or pellets. Furthermore, Sarawak, Malaysia is currently one of the largest exporters of sago products in the world, with annual exports of approximately 25,000 to 40,000 tonnes to Peninsular Malaysia, Japan, Taiwan, and Singapore [31,32]. Nevertheless, it is expected that this value will increase every year, corresponding to the global demand, and will consequently increase the amount of waste produced. During the processing of sago starch, three major by-products are generated, namely sago trunk bark, fibrous pith residue, also known as hampas, and wastewater. It is estimated that for every tonne of sago flour produced, 0.75 tonnes of sago bark waste are created [33]. Sago bark waste is commonly incinerated for power generation in sago mills, deposited directly into nearby rivers, or left for natural degradation outside sago mills [34]. Annually, approximately 20,000 tonnes of sago bark are discarded from Malaysia’s sago industry [35]. To ameliorate P fixation and to maximise the exploitation of agro-industrial waste as higher value-added products, charcoal and sago bark ash can be used as soil amendments. The application of soil amendments such as biochar, compost, and manures have been Agronomy 2021, 11, 1803 3 of 28

reported to improve soil chemical properties and particularly enhancing P availability via a reduction in P sorption sites [36–38]. Addition of these amendments to soils can promote soil fertility and crop productivity, improve soil aggregation and structure, increase pH buffering capacity, cation exchange capacity, soil water retention, bioavailability of immobile nutrients, and carbon sequestration [39–41]. The highly porous structure of charcoal is resilient to biotic degradation, and this enables it to serve as a carbon storage medium in ecosystems for a long time [42,43]. The abundance of pores in charcoals enable air retention, hence creating an aerobic condition in the soil [44]. Moreover, these pores are able to adsorb toxic substances such as phenolics, Al, and Fe ions, thus avoiding the inhibition of fine roots and hyphae of arbuscular mycorrhizae and ectomycorrhizae development [45–48]. In addition, the pores indirectly improve nutrient retention through adsorbing and holding water [49–51]. Charcoal can also neutralise soil pH, which is essential for crop production in acidic soils [46,50,52]. Similarly, ash can neutralise the acidity of soils because of the presence of neutralising compounds such as calcite (CaCO3), fairchildite (K2Ca(CO3)2), lime (CaO), and magnesium oxide (MgO) [53,54]. Demeyer et al. [55] specified that high concentrations of P, Ca, Mg, and K in wood ash is valuable for soils which are naturally low in nutrients. In addition, wood ash increases basic cation saturation in forest soils [56–58]. Ferriero et al. [59] found that the concentrations of trace elements such as Mn, Zn, and B increased with the application of wood ash. Moreover, ash is reported to enhance microbial activity in the soil, which may favour nutrient availability [55]. It was hypothesised that combined application of charcoal and sago bark ash at the correct amount will be able to increase P availability, at the same time fixing Al and Fe ions. The research question to be addressed in this study is how much charcoal and sago bark ash are needed to unlock fixed P by Al and Fe ions. The implications of including charcoal and sago bark ash as soil amendments is not only an attempt to develop new practices that could put agro-industrial wastes to good use, but also to provide a deeper understanding on the mechanism involves in mitigating high P fixation of acidic soils. A holistic understanding of the relationships and interactions of the various P pools in soils and the numerous factors that influence P availability is essential for optimising P management and improving P use efficiency. Therefore, this study was focused on optimising charcoal and sago bark ash to increase P availability in acidic soils.

2. Materials and Methods 2.1. Soil Sampling, Preparation, and Selected Physico-Chemical Analyses The soil (Bekenu Series, Typic Paleudults) used in this study was taken from an unculti- vated secondary forest of Universiti Putra Malaysia Bintulu Sarawak Campus (UPMKB) on geographical coordinate of 3◦1202000 N, 113◦0402000 E (Figure1). This soil was selected because it is commonly cultivated with different crops in Malaysia although it is charac- terised by high P-ﬁxing because of high Al and Fe contents. The area has an elevation of 27.3 m, an annual rainfall of 2993 mm, a mean temperature of 27 ◦C, and a relative humidity of approximately 80%. The soil was randomly sampled with speciﬁcations of 1 m length × 1 m width at depth of 0–20 cm using a shovel. Ten sacks of soil were sampled, each containing approximately 10 kg of soil. Thereafter, the soil was air-dried, crushed manually, and sieved through a 2 mm sieve. The soil was analysed for soil bulk density using the coring method [60]. Soil texture was determined using the hydrometer method [61]. Soil pH in water and KCl and electrical conductivity (EC) were determined at a ratio of 1:2.5 (soil:distilled water/KCl) using a digital pH meter and EC meter [62]. Soil total carbon was calculated as 58% of the organic matter determined using the loss on ignition method [63]. Total N was determined using the Kjeldhal method [64]. The soil cation exchange capacity (CEC) was determined using the leaching method [65] followed by steam distillation [64]. Soil exchangeable acidity, H+, and Al3+ were determined using the acid-base titration method [66]. Agronomy 2021, 11, 1803 4 of 28 Agronomy 2021, 11, x 4 of 28

Figure 1. Aerial view of location where soil was sampled for incubation study in Universiti Putra Malaysia Bintulu Sara- Figure 1. Aerial view of location where soil was sampled for incubation study in Universiti Putra wak Campus, Malaysia. Malaysia Bintulu Sarawak Campus, Malaysia. The soil was analysed for soil bulk density using the coring method [60]. Soil texture Soil total P was extracted using the aqua regia method [67]. The aqua regia solution was determined using the hydrometer method [61]. Soil pH in water and KCl and electri- was prepared by mixing concentrated HCl and concentrated HNO at a ratio of 3:1. A cal conductivity (EC) were determined at a ratio of 1:2.5 3(soil:distilled water/KCl) using a 2 g sample ofdigital soil was pH weighedmeter and and EC meter placed [62]. into Soil a total 250 mLcarbon conical was calculated flask, after as 58% which of the organic 20 mL of aqua regiamatter solution determined was using added. the Thereafter, loss on ignition the suspension method [63]. was Total heated N was on determined a hot using plate until thethe solution Kjeldhal turned method clear. [64]. The The suspension soil cation exchange was filtered capacity using (CEC) into was a 100 determined mL using volumetric flaskthe and leaching diluted method to the [65] required followed volume by steam with distillation distilled water. [64]. Soil Soil exchangeable available P acidity, H+, + 2+ 2+ + 2+ 2+ and exchangeableand cations Al3+ were (K determined, Ca , Mg using, Na the, Mn acid-base, and Fetitration) were method extracted [66]. using the Mehlich No.1 doubleSoil acid total method P was [extracted68]. The using double the acid aqua solution regia method (mixture [67]. of The 0.05 aqua M HCl regia solution and 0.025 M H2wasSO4 )prepared was prepared by mixing by mixing concentrated 4.12 mL HCl of concentratedand concentrated HCl HNO with3 1.40 at a mLratio of of 3:1. A 2 g concentrated H2sampleSO4 in of a 1000soil was mL volumetricweighed and flask placed and into diluted a 250 to mL the conical required flask, volume after withwhich 20 mL of distilled water.aqua A 5 g regia sample solution of soil was was added. weighed Thereafter, and placed the suspension into a plastic was vial, heated after on which a hot plate until 20 mL of doublethe acid solution solution turned was clear. added. The suspension Afterwards, was thefiltered suspension using into was a 100 shaken mL volumetric at flask 180 rpm for 10and min. diluted The to suspension the required was volume filtered with into dist ailled plastic water. vial Soil using available filter P and paper. exchangeable Series of extractantscations were (K+,used Ca2+, toMg fractionate2+, Na+, Mn pools2+, andof Fe inorganic2+) were extracted P following using the the sequential Mehlich No.1 double extraction methodacid describedmethod [68]. by The Kuo double [69]. Loosely acid soluti solubleon (mixture P (Sol-P) of 0.05 was M removed HCl and using 0.025 M H2SO4) 1 M NH4Cl. Aluminium-boundwas prepared by mixing P (Al-P) 4.12 was mL separatedof concentrated from HCl iron-bound with 1.40 PmL (Fe-P) of concentrated using H2SO4 0.5 M NH4F at ain pH a 1000 of 8.2, mL then volumetric Fe-P was flask removed and diluted using to 0.1 the M required NaOH. volume Reductant with soluble distilled water. A P (Red-P) was extracted5 g sample using of soil 0.3 was M sodiumweighed citrate and placed (Na3C into6H5 aO plastic7), 1 M vial, sodium after bicarbonatewhich 20 mL of double (NaHCO3), andacid sodium solution dithionate was added. (Na Afterwards,2S2O4). Calcium-bound the suspension P was (Ca-P) shaken was at extracted 180 rpm for 10 min. using 0.25 M HThe2SO 4suspension, whereas forwas occluded filtered into P (Occl-P), a plastic 0.1vial M using NaOH filter was paper. used. Series of extractants were Soil total P,used Mehlich-P, to fractionate and inorganic pools of Pinorganic concentration P following were determined the sequential using extraction UV-VIS method de- Spectrophotometerscribed (Perkin by Kuo Elmer [69]. Lambda Loosely 25,soluble Waltham, P (Sol-P) MA, was USA) removed at 882 nmusing wavelength 1 M NH4Cl. Alumin- after a blue colourium-bound was developed P (Al-P) usingwas separated the molybdenum from iron-bound blue method P (Fe-P) [70 using]. Acid 0.5 M molyb- NH4F at a pH of date stock solution8.2, then (Reagent Fe-P was A) and removed ascorbic using acid 0.1 stock M NaOH. solution Reductant (Reagent soluble B) were P (Red-P) prepared was extracted for the blue colourusing development 0.3 M sodium procedure. citrate (Na3 AC6H standard5O7), 1 M P sodium solution bicarbonate (standard (NaHCO solution3), 1) and sodium and standard solutiondithionate 2 were(Na2S prepared2O4). Calcium-bound and used toP (Ca-P) prepare was working extracted solutions using 0.25 ranging M H2SO4, whereas from 0 to 0.6 ppm.for occluded In thisprocess, P (Occl-P), 1 to0.1 6 M mL NaOH of standard was used. solution 2 was pipetted into a 50 mL volumetric flaskSoil containingtotal P, Mehlich-P, 8 mL of and Reagent inorganic B and P dilutedconcentration to the requiredwere determined volume using UV- VIS Spectrophotometer (Perkin Elmer Lambda 25, Waltham, MA, USA) at 882 nm wave- with distilled water. Afterwards, 8 mL of Reagent B was pipetted into a different 50 mL length after a blue colour was developed using the molybdenum blue method [70]. Acid volumetric flask, after which the sample was added depending on the intensity of the blue molybdate stock solution (Reagent A) and ascorbic acid stock solution (Reagent B) were colour to be developed. The solution was diluted to the required volume with distilled prepared for the blue colour development procedure. A standard P solution (standard water. Soil exchangeable cations were determined using atomic absorption spectrometry solution 1) and standard solution 2 were prepared and used to prepare working solutions (AAS) (Analyst 800, Perkin Elmer, Norwalk, CT, USA). The physico-chemical properties of ranging from 0 to 0.6 ppm. In this process, 1 to 6 mL of standard solution 2 was pipetted the soil used in this present study were within the range reported by Paramananthan [71], into a 50 mL volumetric flask containing 8 mL of Reagent B and diluted to the required except for soil texture.volume Thewith selected distilled physico-chemical water. Afterwards, properties 8 mL of Reagent of the soil B was are summarisedpipetted into a different in Table1. The percentages of the inorganic P fractions in the soil before the incubation

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study are summarised in Table2, where the order of the P fraction was Fe-P > Occl-P > Al-P > Ca-P > Red-P > Sol-P.

Table 1. Selected physico-chemical properties of the soil used in incubation study.

Property Value Obtained Standard Range * pH (water) 4.61 4.6–4.9 pH (KCl) 3.95 3.8–4.0 EC (µS cm−1) 35.10 NA Bulk density (g cm−1) 1.25 NA Total carbon (%) 2.16 0.57–2.51 Total N (%) 0.08 0.04–0.17 Total P (mg kg−1) 23.65 NA Available P (mg kg−1) 1.13 NA CEC 4.67 3.86–8.46 Exchangeable acidity 1.15 NA Exchangeable Al3+ 1.02 NA Exchangeable H+ 0.13 NA Exchangeable K+ 0.06 0.05–0.19 cmol kg−1 Exchangeable Ca2+ 0.02 0.01 Exchangeable Mg2+ 0.22 0.07–0.21 Exchangeable Na+ 0.03 0.01 Exchangeable Mn2+ 0.01 NA Exchangeable Fe2+ 1.09 NA Sand (%): 71.9 Sand (%): 72–76 Silt (%): 13.5 Silt (%): 8–9 Soil texture Clay (%): 14.6 Clay (%): 16–19 Sandy loam Sandy clay loam Note: * Standard range subjected to the soil development by Paramananthan [71]; NA: not available; Available P: P that was extracted using Mehlich 1 method (Mehlich-P).

Table 2. Percentages of inorganic phosphorus speciation in soil before incubation study.

Inorganic Phosphorus Percentage (%) Loosely soluble phosphorus (Sol-P) 0 Aluminium bound phosphorus (Al-P) 11 Iron bound phosphorus (Fe-P) 67 Reductant soluble phosphorus (Red-P) 3 Calcium bound phosphorus (Ca-P) 7 Occluded phosphorus (Occl-P) 12 Total 100

2.2. Charcoal and Sago Bark Ash Characterisation The charcoal used in this study was obtained from Pertama Ferroalloys Sdn Bhd, Bintulu, Sarawak, Malaysia, whereas the sago bark ash was purchased from Song Ngeng Sago Industries, Dalat, Sarawak, Malaysia. Afterwards, the amendments were analysed for pH in water and in KCl, EC [62], available P [68,70], and exchangeable K+, Ca2+, Mg2+, Na+, and Fe2+ [68]. The results of these analyses are presented in Table3. Agronomy 2021, 11, 1803 6 of 28

Table 3. Selected chemical properties of charcoal and sago bark ash.

Property Charcoal Sago Bark Ash pH (water) 7.74 9.99 pH (KCl) 7.31 9.66 EC (dS m−1) 0.27 5.75 Available P (mg kg−1) 31.25 55.83 Exchangeable K+ 3.67 23.33 Exchangeable Ca2+ 11.71 16.77 Exchangeable Mg2+ cmol kg−1 3.37 3.57 Exchangeable Na+ 0.43 1.51 Exchangeable Fe2+ 0.15 0.03 Note: Available P: P that was extracted using Mehlich 1 method (Mehlich-P).

2.3. Incubation Set Up A laboratory incubation study was conducted in the Soil Science Laboratory of UPMKB. A 1 kg sample of soil (from the 2 mm bulked soil sample) was weighed in a polypropylene container. Egypt rock phosphate, charcoal, and sago bark ash were added and thoroughly mixed according to the treatment evaluated in this present study. The samples were moistened to 60% of moisture content based on the soil field capacity. The lids of the polypropylene containers were perforated to allow good aeration. The samples were incubated at room temperature (26 ◦C) for 30, 60, and 90 days. The recommended −1 −1 rate of the P fertiliser used was 60 kg P2O5 ha (214 kg ha ERP). This rate was based on the standard recommendation for maize (Zea mays L.) cultivation [72]. Maize was chosen as the test crop because of its sensitivity, which can reflect nutrient recovery, uptake, and efficiency and rapid response towards nutrient deficiency. The rate at which the fertilisers were applied in the incubation study was scaled down to a per plant basis (based on planting density of 27,777 plants ha−1), which was equivalent to 7.7 g of ERP plant−1. The amounts of the amendments used were deduced from the literature (charcoal [73,74] and sago bark ash [75–77]) where 10 and 5 t ha−1 equivalent to 51.4 and 25.7 g, respectively, in 1 kg of soil per container. The charcoal and sago bark ash rates were varied by 25%, whereas the ERP rate was fixed at 100% of the recommendation rate in all treatments except for T1 (no ERP applied). The treatments evaluated in this present study are summarised as follows: T1: Soil only T2 Soil + ERP T3 Soil + ERP + 51.4 g charcoal T4 Soil + ERP + 25.7 g sago bark ash T5 Soil + ERP + 51.4 g charcoal + 25.7 g sago bark ash T6: Soil + ERP + 38.6 g charcoal + 19.3 g sago bark ash T7: Soil + ERP + 25.7 g charcoal + 19.3 g sago bark ash T8: Soil + ERP + 12.9 g charcoal + 19.3 g sago bark ash T9: Soil + ERP + 38.6 g charcoal + 12.9 g sago bark ash T10: Soil + ERP + 25.7 g charcoal + 12.9 g sago bark ash T11: Soil + ERP + 12.9 g charcoal + 12.9 g sago bark ash T12: Soil + ERP + 38.6 g charcoal + 6.4 g sago bark ash T13: Soil + ERP + 25.7 g charcoal + 6.4 g sago bark ash T14: Soil + ERP + 12.9 g charcoal + 6.4 g sago bark ash

2.4. Experimental Design and Statistical Analysis The treatments were arranged in a completely randomised design (CRD) with three replications. Normality test was used to determine if the data set is well-modelled by a normal distribution. Analysis of variance (ANOVA) was used to detect treatment effects, whereas treatments means were compared using Tukey’s Studentized range (HSD) test at p ≤ 0.05. The statistical software used was Statistical Analysis System (SAS) version 9.4. Agronomy 2021, 11, 1803 7 of 28

3. Results 3.1. Effects of Amending Egypt Rock Phosphate with Charcoal and Sago Bark Ash on Selected Soil Chemical Properties The effects of treatments on soil total carbon (TC) at 30, 60, and 90 days of incubation (DAI) are presented in Figure2. There was no signiﬁcant difference in TC for T1 and T2, regardless of incubation period. The treatment with the sago bark ash alone (T4) demon- Agronomy 2021, 11, x FOR PEER REVIEW strated lower contribution towards TC. At 30 DAI, the effects8 of of28 T3, T5, and T12 on TC

were similar but signiﬁcantly higher than those of T1, T2, T4, T6, T7, T8, T9, T10, T11, T13, and T14. Although T5 had higher content of TC, the effect was not signiﬁcantly different Amongcompared the treatments, to T9 at T1 60 had DAI the and highest T3 andsoil exchangeable T12 at 90 DAI. Fe2+ at Throughout 30, 60, and 90 the 288 incubation study, the DAI (Figure 8). Upon application of charcoal and sago bark ash, soil exchangeable Fe2+ 289 TC of the treatments with 25% charcoal (T8, T11, and T14) was, similar irrespective of the reduced. There was no significant difference in soil exchangeable Fe2+ between T2 and T3, 290 irrespectiveamount of incubation of sago time. bark ash used. 291 292 Commented [PDBJ10]: Please, this is a new Figure 2 because the axis name has been changed from “soil total organic carbon” to “soil total carbon”

293 Figure 2. Effects of treatments on soil total carbon after thirty, sixty, and ninety days of incubation, 294 where T1: Figure 2. Treatments on soil total organic carbon after thirty, sixty, and ninety days of incubation, where T1: soil 295 Commented [PDBJ11]: Please change “total soil alone, T2: Egyptalone, rock T2: phosphateEgypt rock phosphate alone, alone, T3: T3: Egypt Egypt rock rock phosphate phosphate + 100% charcoal, + 100% T4: charcoal,Egypt rock phosphate T4: Egypt + 296 rock phosphate + 100% sago bark ash, and100% T5: sago Egypt bark ash, rock and phosphateT5: Egypt rock + phosphate 100% charcoal + 100% charcoal + 100% + 100% sago sago bark bark ash, ash, T6: T6: Egypt Egypt rockrock 297 phosphateorganic carbon” + 75% to “total carbon” phosphate + 75% charcoal + 75% sago bark ash, T7: Egypt rock phosphate + 50% charcoal + 75% sago bark ash, 298 charcoal + 75% sagoT8: bark Egypt ash, rock T7: phosphate Egypt + 25% rock charcoal phosphate + 75% sago + bark 50% ash, charcoal T9: Egypt rock + 75% phosphate sago + bark75% charcoal ash, T8:+ 50% Egypt 299 rock phosphate + 25% charcoal + 75%sago sago bark ash, bark T10: ash, Egypt T9: rock Egyptphosphate rock + 50%phosphate charcoal + 50% sago + 75% bark charcoalash, T11: Egypt + 50%rock phosphate sago bark + 25% ash, 300 T10: Egypt rock charcoal + 50% sago bark ash, T12: Egypt rock phosphate + 75% charcoal + 25% sago bark ash, T13: Egypt rock 301 phosphate + 50% charcoalphosphate + + 50%50% charcoal sago + bark 25% sago ash, bark T11: ash, and Egypt T14: Egypt rock rock phosphate phosphate + +25% 25% charcoal charcoal + 25% sago + bark 50% sago302 bark ash, T12: Egypt rock phosphateash +. Means 75% with charcoal different + letter(s) 25% sago within bark the same ash, incubation T13: Egypt period indicate rockphosphate significant difference + 50% between charcoal 303 + 25% sago bark treatments by Tukey’s HSD test at p ≤ 0.05, i.e., a > b > c. Bars represent the mean values ± SE. 304 ash, and T14: Egypt rock phosphate + 25% charcoal + 25% sago bark ash. Means with different letter(s) 305 within the same incubation period indicate signiﬁcant differences between treatments according to Tukey’s HSD test at p ≤ 0.05, i.e., a > b > c. Bars represent the mean values ± SE.

Figures3 and4 suggest that the treatments without soil amendments (T1 and T2) had significantly lower pH compared with the treatments with the soil amendments (T3, T4, T5, T6, T7, T8, T9, 10, T11, T12, T13, and T14). At 30 and 60 DAI, the soil pH for T5 was significantly higher than other treatments with charcoal and sago bark ash. At 90 DAI, the effect of the treatment with sago bark ash alone (T4) on soil pH was not significantly different compared to the treatments with the combined use of charcoal and sago bark ash at 100% (T5) and the combination of charcoal and sago bark ash at 75% (T6). Among the 306 Figure 3. Treatmentstreatments on soil with pH in water the after soil thirty amendments,, sixty, and ninety days the of treatment incubation, where with T1: soil charcoal alone, 307 alone (T3) had lower T2: Egypt soilrock phosphate pH, regardless alone, T3: Egypt of rock incubation phosphate + period.100% charcoal, T4: Egypt rock phosphate + 100% 308 sago bark ash, and T5: Egypt rock phosphate + 100% charcoal + 100% sago bark ash, T6: Egypt rock phosphate + 309 75% charcoal + 75% sago bark ash, T7: Egypt rock phosphate + 50% charcoal + 75% sago bark ash, T8: Egypt rock 310 phosphate + 25% charcoal + 75% sago bark ash, T9: Egypt rock phosphate + 75% charcoal + 50% sago bark ash, 311 T10: Egypt rock phosphate + 50% charcoal + 50% sago bark ash, T11: Egypt rock phosphate + 25% charcoal + 50% 312 sago bark ash, T12: Egypt rock phosphate + 75% charcoal + 25% sago bark ash, T13: Egypt rock phosphate + 50% 313 charcoal + 25% sago bark ash, and T14: Egypt rock phosphate + 25% charcoal + 25% sago bark ash. Means with 314 different letter(s) within the same incubation period indicate significant difference between treatments by Tuk- 315 ey’s HSD test at p ≤ 0.05, i.e., a > b > c. Bars represent the mean values ± SE. 316 317

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treatments with the soil amendments, the treatment with charcoal alone (T3) had lower soil pH, regardless of incubation period. Agronomy 2021, 11, 1803 8 of 28 treatments with the soil amendments, the treatment with charcoal alone (T3) had lower soil pH, regardless of incubation period.

Figure 3. Effects of treatments on soil pH in water after thirty, sixty, and ninety days of incubation, where T1: soil alone, T2: Egypt rock phosphate alone, T3: Egypt rock phosphate + 100% charcoal, T4: Egypt rock phosphate + 100% sago bark ash, and T5: Egypt rock phosphate + 100% charcoal + FigureFigure 3. Effects 3. ofEffects treatments of treatments on soil pH on in soil water pH after in water thirty, after sixty, thirty, and ninety sixty, days and of ninety incubation, days of where incubation, T1: soil alone, 100% sago bark ash, T6: Egypt rock phosphate + 75% charcoal + 75% sago bark ash, T7: Egypt rock T2: Egyptwhere rock T1: phosphate soil alone, alone, T2: T3: Egypt Egypt rock rock phosphate phosphate +alone, 100% T3: charcoal, Egypt T4: rock Egypt ph rockosphate phosphate + 100% + 100%charcoal, sago bark phosphate + 50% charcoal + 75% sago bark ash, T8: Egypt rock phosphate + 25% charcoal + 75% sago ash, andT4: T5: Egypt Egypt rock rock phosphate + + 100% 100% charcoal sago bark + 100% ash, sago and bark T5: ash, Egypt T6: Egyptrock phosphate rock phosphate + 100% + 75% charcoal charcoal + + 75% bark ash, T9: Egypt rock phosphate + 75% charcoal + 50% sago bark ash, T10: Egypt rock phosphate sago bark100% ash, sago T7: Egyptbark ash, rock T6: phosphate Egypt rock + 50% phosphate charcoal + + 75% 75% sago charcoal bark ash, + 75% T8: sago Egypt bark rock ash, phosphate T7: Egypt + 25% rock charcoal + 50% charcoal + 50% sago bark ash, T11: Egypt rock phosphate + 25% charcoal + 50% sago bark ash, + 75% sagophosphate bark ash, + 50% T9: charcoal Egypt rock + 75% phosphate sago bark + 75% ash, charcoal T8: Egypt + 50% rock sago phosphate bark ash, T10:+ 25% Egypt charcoal rock + phosphate 75% sago + 50% T12: Egypt rock phosphate + 75% charcoal + 25% sago bark ash, T13: Egypt rock phosphate + 50% charcoalbark + 50% ash, sago T9: barkEgypt ash, rock T11: phosphate Egypt rock phosphate+ 75% charcoal + 25% + charcoal 50% sago + 50% bark sago ash, bark T10: ash, Egypt T12: Egyptrock phosphate rock phosphate + charcoal + 25% sago bark ash, and T14: Egypt rock phosphate + 25% charcoal + 25% sago bark ash. 75% charcoal+ 50% charcoal + 25% sago + 50% bark sago ash, T13:bark Egypt ash, T11: rock Egypt phosphate rock + phosphate 50% charcoal + 25% + 25% charcoal sago bark + 50% ash, sago and T14:bark Egypt ash, rock Means with different letter(s) within the same incubation period indicate significant differences be- phosphateT12: +Egypt 25% charcoal rock phosphate + 25% sago + bark75% ash.charcoal Means + with25% different sago bark letter(s) ash, withinT13: Egypt the same rock incubation phosphate period + 50% indicate tween treatments according to Tukey’s HSD test at p ≤ 0.05, i.e., a > b > c. Bars represent the mean charcoal + 25% sago bark ash, and T14: Egypt rock phosphatep +≤ 25% charcoal + 25% sago bark ash. signiﬁcantvalues differences ± SE. between treatments according to Tukey’s HSD test at 0.05, i.e., a > b > c. Bars represent the mean valuesMeans± SE. with different letter(s) within the same incubation period indicate significant differences between treatments according to Tukey’s HSD test at p ≤ 0.05, i.e., a > b > c. Bars represent the mean values ± SE.

FigureFigure 4. Effects 4. ofEffects treatments of treatments on soil pH on in soil potassium pH in potassium chloride after chloride thirty, sixty,after andthirty, ninety sixty, days and of ninety incubation, days where T1: soilof alone, incubation, T2: Egypt where rock phosphateT1: soil alone, alone, T2: T3: Egypt Egypt ro rockck phosphatephosphate + alone, 100% charcoal,T3: Egypt T4: rock Egypt phosphate rock phosphate + + 100% sago bark ash, and T5: Egypt rock phosphate + 100% charcoal + 100% sago bark ash, T6: Egypt rock phosphate + 75% 100%Figure charcoal, 4. Effects T4: of treatmentsEgypt rock onphosphate soil pH in+ 100%potassium sago chloridebark ash, after and thirty, T5: Egypt sixty, rock and phosphate ninety days + charcoal + 75% sago bark ash, T7: Egypt rock phosphate + 50% charcoal + 75% sago bark ash, T8: Egypt rock phosphate 100%of incubation, charcoal +where 100% T1:sago soil bark alone, ash, T2:T6: Egypt rockrock phosphatephosphate + alone, 75% charcoal T3: Egypt + 75% rock sago phosphate bark ash, + + 25% charcoal + 75% sago bark ash, T9: Egypt rock phosphate + 75% charcoal + 50% sago bark ash, T10: Egypt rock T7:100% Egypt charcoal, rock T4:phosphate Egypt rock + 50% phosphate charcoal ++ 100%75% sasagogo barkbark ash,ash, T8:and Egypt T5: Egypt rock rockphosphate phosphate + 25% + phosphate + 50% charcoal + 50% sago bark ash, T11: Egypt rock phosphate + 25% charcoal + 50% sago bark ash, T12: charcoal100% charcoal + 75% + sago 100% bark sago ash, bark T9: ash, Egypt T6: Egyptrock phos rockphate phosphate + 75% + charcoal 75% charcoal + 50% + sago75% sagobark barkash, T10:ash, Egypt rock phosphate + 75% charcoal + 25% sago bark ash, T13: Egypt rock phosphate + 50% charcoal + 25% sago bark EgyptT7: Egypt rock rock phosphate phosphate + 50% + 50%charcoal charcoal + 50% + sago75% basagork ash,bark T11: ash, Egypt T8: Egypt rock phosphaterock phosphate + 25% + char- 25% ash, and T14: Egypt rock phosphate + 25% charcoal + 25% sago bark ash. Means with different letter(s) within the same coalcharcoal + 50% + sago75% sagobark ash,bark T12: ash, Egypt T9: Egypt rock rockphosphat phosephate + 75% + charcoal75% charcoal + 25% + sago 50% bark sago ash, bark T13: ash, Egypt T10: incubation period indicate signiﬁcant differences between treatments according to Tukey’s HSD test at p ≤ 0.05, i.e., rockEgypt phosphate rock phosphate + 50% charcoal+ 50% charcoal + 25% sago+ 50% bark sago as bah, rkand ash, T14: T11: Egypt Egypt rock rock phosphate phosphate + 25% + 25% charcoal char- a > b > c. Bars represent the mean values ± SE. +coal 25% + 50%sago sago bark bark ash. ash,Means T12: with Egypt different rock phosphat letter(s)e within + 75% charcoalthe same + incubation 25% sago bark period ash, indicate T13: Egypt sig- nificantrock phosphate differences + 50% between charcoal treatments + 25% sago according bark as h,to andTukey’s T14: HSDEgypt test rock at phosphatep ≤ 0.05, i.e., + a25% > b charcoal> c. Bars represent+ 25% sago the bark mean ash. values Means ± SE.with different letter(s) within the same incubation period indicate significant differences between treatments according to Tukey’s HSD test at p ≤ 0.05, i.e., a > b > c. Bars represent the mean values ± SE.

Agronomy 2021, 11, x 9 of 28

Agronomy 2021, 11, 1803 9 of 28 The interaction between the time of incubation and treatment significantly affected soil exchangeable acidity (Figure 5). Among the treatments, T1 recorded the highest soil

exchangeable acidity followedThe interaction by T2. between Soil exchangeable the time of incubation acidity andincreased treatment as significantly the amount affected of sago bark was reducedsoil exchangeable from 100% acidity to 75%, (Figure 50%,5). Among and 25%. the treatments, Throughout T1 recorded the incubation the highest soil study, the effect of exchangeablethe treatment acidity with followed charcoal by T2.alone Soil exchangeableat the rate of acidity 100% increased (T3) on as soil the amount ex- of changeable acidity wassago barknot significantly was reduced from different 100% to compared 75%, 50%, and to 25%. treatment Throughout with the the incubation combi- study, nation of charcoal atthe 75%, effect 50%, of the and treatment 25% and with charcoalsago bark alone ash at theat 25% rate of (T12, 100% T13, (T3) onand soil T14). exchangeable A acidity was not significantly different compared to treatment with the combination of 3+ 3+ similar trend was alsocharcoal found at in 75%, soil 50%, exchangeable and 25% and Al sago (Figure bark ash 6). at 25%Soil (T12,exchangeable T13, and T14). Al A of similar soil alone (T1) and ERPtrend alone was also (T2) found were in soilsignificantly exchangeable higher Al3+ (Figure than those6). Soil with exchangeable charcoal Al and3+ of soil sago bark ash. Betweenalone T1 (T1) and and T2, ERP T2 alone demonstrated (T2) were significantly significantly higher lower than those soil with exchangeable charcoal and sago 3+ Al3+. Regardless of barkthe incubation ash. Between period, T1 and T2, soil T2 demonstratedexchangeable significantly Al3+ for lowerthe treatment soil exchangeable with Al . Regardless of the incubation period, soil exchangeable Al3+ for the treatment with sago sago bark ash alonebark (T4) ash was alone not (T4) significantly was not significantly different different compared compared to tothe the treatments treatments with with charcoal charcoal and sago barkand sagoash. bark ash.

FigureFigure 5. Effects 5. Effects of treatments of treatments on soil exchangeable on soil exchangeable acidity after thirty, acidity sixty, after and ninetythirty, days sixty, of incubation, and ninety where days T1: soilof alone,incubation, T2: Egypt where rock phosphate T1: soil alone,alone, T3: T2: Egypt Egypt rock rock phosphate phosphate + 100% alone, charcoal, T3: T4: Egypt Egypt rock phosphate phosphate + 100% + 100% sago barkcharcoal, ash, and T4: T5: EgyptEgypt rock rock phosphate phosphate + 100% + charcoal100% sago + 100% bark sago ash, bark and ash, T6:T5: Egypt Egypt rock rock phosphate phosphate + 75% charcoal+ 100% + 75%charcoal sago bark + ash,100% T7: sago Egypt bark rock phosphateash, T6: Egypt + 50% charcoal rock ph +osphate 75% sago bark+ 75% ash, charcoal T8: Egypt + rock 75% phosphate sago bark + 25% ash, charcoal T7: +Egypt 75% sago rock bark phosphate ash, T9: Egypt + 50% rock charcoal phosphate + 75% + 75% sago charcoal bark + ash, 50% sagoT8: Egypt bark ash, rock T10: phosphate Egypt rock + phosphate 25% charcoal + 50% charcoal + 50% sago bark ash, T11: Egypt rock phosphate + 25% charcoal + 50% sago bark ash, T12: Egypt rock phosphate + + 75% sago bark ash, T9: Egypt rock phosphate + 75% charcoal + 50% sago bark ash, T10: Egypt rock 75% charcoal + 25% sago bark ash, T13: Egypt rock phosphate + 50% charcoal + 25% sago bark ash, and T14: Egypt rock phosphate + 50% charcoal + 50% sago bark ash, T11: Egypt rock phosphate + 25% charcoal + 50% phosphate + 25% charcoal + 25% sago bark ash.. Means with different letter(s) within the same incubation period indicate significantsago bark differences ash, T12: between Egypt treatments rock phosphate according to + Tukey’s 75% charcoal HSD test at +p 25%≤ 0.05, sago i.e., abark > b > ash, c. Bars T13: represent Egypt the rock mean valuesphosphate± SE. + 50% charcoal + 25% sago bark ash, and T14: Egypt rock phosphate + 25% charcoal + 25% sago bark ash.. Means with different letter(s) within the same incubation period indicate sig- The effects of treatments on soil exchangeable H+ are demonstrated in Figure7. Soil nificant differences betweenexchangeable treatments H+ for according T1 was significantly to Tukey’s higher HSD than test thoseat p ≤ of0.05, T2, T3,i.e., T4, a > T5, b > T6, c. Bars T7, T8, T9, represent the mean valuesT10,T11, ± SE. T12, T13, and T14 at 30, 60, and 90 DAI. In addition, soil exchangeable H+ of T1 increased with time. There was no significant difference in soil exchangeable H+ for the soil with ERP, charcoal, and sago bark ash, irrespective of incubation time.

Figure 6. Effects of treatments on soil exchangeable aluminium ions after thirty, sixty, and ninety days of incubation, where T1: soil alone, T2: Egypt rock phosphate alone, T3: Egypt rock phosphate

Agronomy 2021, 11, x 9 of 28

The interaction between the time of incubation and treatment significantly affected soil exchangeable acidity (Figure 5). Among the treatments, T1 recorded the highest soil exchangeable acidity followed by T2. Soil exchangeable acidity increased as the amount of sago bark was reduced from 100% to 75%, 50%, and 25%. Throughout the incubation study, the effect of the treatment with charcoal alone at the rate of 100% (T3) on soil exchangeable acidity was not significantly different compared to treatment with the combination of charcoal at 75%, 50%, and 25% and sago bark ash at 25% (T12, T13, and T14). A similar trend was also found in soil exchangeable Al3+ (Figure 6). Soil exchangeable Al3+ of soil alone (T1) and ERP alone (T2) were significantly higher than those with charcoal and sago bark ash. Between T1 and T2, T2 demonstrated significantly lower soil exchangeable Al3+. Regardless of the incubation period, soil exchangeable Al3+ for the treatment with sago bark ash alone (T4) was not significantly different compared to the treatments with charcoal and sago bark ash.

Figure 5. Effects of treatments on soil exchangeable acidity after thirty, sixty, and ninety days of incubation, where T1: soil alone, T2: Egypt rock phosphate alone, T3: Egypt rock phosphate + 100% charcoal, T4: Egypt rock phosphate + 100% sago bark ash, and T5: Egypt rock phosphate + 100% charcoal + 100% sago bark ash, T6: Egypt rock phosphate + 75% charcoal + 75% sago bark ash, T7: Egypt rock phosphate + 50% charcoal + 75% sago bark ash, T8: Egypt rock phosphate + 25% charcoal + 75% sago bark ash, T9: Egypt rock phosphate + 75% charcoal + 50% sago bark ash, T10: Egypt rock phosphate + 50% charcoal + 50% sago bark ash, T11: Egypt rock phosphate + 25% charcoal + 50% sago bark ash, T12: Egypt rock phosphate + 75% charcoal + 25% sago bark ash, T13: Egypt rock phosphate + 50% charcoal + 25% sago bark ash, and T14: Egypt rock phosphate + 25% charcoal +

Agronomy 202125%, 11, 1803sago bark ash.. Means with different letter(s) within the same incubation period indicate sig- 10 of 28 nificant differences between treatments according to Tukey’s HSD test at p ≤ 0.05, i.e., a > b > c. Bars represent the mean values ± SE.

Agronomy 2021, 11, x 10 of 28

+ 100% charcoal, T4: Egypt rock phosphate + 100% sago bark ash, and T5: Egypt rock phosphate + 100% charcoal + 100% sago bark ash, T6: Egypt rock phosphate + 75% charcoal + 75% sago bark ash, T7: Egypt rock phosphate + 50% charcoal + 75% sago bark ash, T8: Egypt rock phosphate + 25% charcoal + 75% sago bark ash, T9: Egypt rock phosphate + 75% charcoal + 50% sago bark ash, T10: Egypt rock phosphate + 50% charcoal + 50% sago bark ash, T11: Egypt rock phosphate + 25% charcoal + 50% sago bark ash, T12: Egypt rock phosphate + 75% charcoal + 25% sago bark ash, T13: Egypt rock phosphate + 50% charcoal + 25% sago bark ash, and T14: Egypt rock phosphate + 25% charcoal + 25% sago bark ash.. Means with different letter(s) within the same incubation period indicate significant differences between treatments according to Tukey’s HSD test at p ≤ 0.05, i.e., a > b > c. Bars represent the mean values ± SE.

The effects of treatments on soil exchangeable H+ are demonstrated in Figure 7. Soil Figure 6. Effects of treatments on soil exchangeable aluminium ions after thirty, sixty, and ninety Figureexchangeable 6. Effects of treatments H+ for on T1 soil was exchangeable significantly aluminium higher ions than after thirty,those sixty, of T2, and T3, ninety T4, days T5, of T6, incubation, T7, T8, where T1: soildays alone, of T2:incubation, Egypt rock where phosphate T1: soil alone, alone, T3: T2: Egypt Egyp rockt rock phosphate phosphate + 100% alone, charcoal, T3: Egypt T4: Egypt rock rockphosphate phosphate + T9, T10, T11, T12, T13, and T14 at 30, 60, and 90 DAI. In addition, soil exchangeable H+ of 100% sago bark ash, and T5: Egypt rock phosphate + 100% charcoal + 100% sago bark ash, T6: Egypt rock phosphate + 75% T1 increased with time. There was no significant difference in soil exchangeable H+ for the charcoal + 75% sago bark ash, T7: Egypt rock phosphate + 50% charcoal + 75% sago bark ash, T8: Egypt rock phosphate + 25%soil charcoal with + 75%ERP, sago charcoal, bark ash, and T9: sago Egypt bark rock ash, phosphate irrespective + 75% charcoal of incubation + 50% sago time. bark ash, T10: Egypt rock 2+ phosphate +Among 50% charcoal the +treatments, 50% sago bark T1 ash,had T11: the Egypt highest rock soil phosphate exchangeable + 25% charcoal Fe +at 50% 30, sago60, barkand ash,90 T12: EgyptDAI rock phosphate(Figure 8). + 75% Upon charcoal application + 25% sago of bark charcoal ash, T13: and Egypt sago rock bark phosphate ash, soil + 50% exchangeable charcoal + 25% Fe sago2+ bark ash, andreduced. T14: Egypt There rock was phosphate no significant + 25% charcoal difference + 25% in sago soil bark exchangeable ash.. Means Fe with2+ between different letter(s) T2 and within T3, the same incubationirrespective period of indicateincubation signiﬁcant time. differences between treatments according to Tukey’s HSD test at p ≤ 0.05, i.e., a > b > c. Bars represent the mean values ± SE.

FigureFigure 7. Effects 7. ofEffects treatments of treatments on soil exchangeable on soil exchangeable hydrogen ions hy afterdrogen thirty, ions sixty, after and ninetythirty, days sixty, of incubation,and ninety where T1: soildays alone, of T2:incubation, Egypt rock where phosphate T1: soil alone, alone, T3: T2: Egypt Egyp rockt rock phosphate phosphate + 100% alone, charcoal, T3: Egypt T4: Egypt rock rockphosphate phosphate + 100% sago+ 100% bark charcoal, ash, and T5: T4: Egypt Egypt rock rock phosphate phosphate + 100% + 100% charcoal sago + 100%bark sagoash, barkand ash,T5: Egypt T6: Egypt rock rock phosphate phosphate + + 75% charcoal100% + 75% charcoal sago bark + 100% ash, T7:sago Egypt bark rock ash, phosphate T6: Egypt + rock 50% phosphate charcoal + 75% + 75% sago charcoal bark ash, + 75% T8: Egypt sago rockbark phosphateash, + 25%T7: charcoal Egypt + 75%rock sago phosphate bark ash, + T9:50% Egypt charcoal rock + phosphate 75% sago + bark 75% charcoalash, T8: +Egypt 50% sago rock bark phosphate ash, T10: + Egypt25% rock phosphatecharcoal + 50% + charcoal 75% sago + 50% bark sago ash, bark T9: ash, Egypt T11: rock Egypt phos rockphate phosphate + 75% + 25% charcoal charcoal + 50% + 50% sago sago bark bark ash, T12:T10: Egypt rock phosphateEgypt rock + 75% phosphate charcoal + 25%50% sagocharcoal bark ash,+ 50% T13: sago Egypt bark rock ash, phosphate T11: Egypt + 50% rock charcoal phosphate + 25% sago+ 25% bark char- ash, and T14: Egyptcoal rock+ 50% phosphate sago bark + 25%ash, charcoalT12: Egypt + 25% rock sago phosphat bark ash.e + Means 75% charcoal with different + 25% letter(s) sago bark within ash, the T13: same Egypt incubation periodrock indicate phosphate signiﬁcant + 50% differences charcoal between + 25% treatmentssago bark as accordingh, and T14: to Tukey’s Egypt HSDrock testphosphate at p ≤ 0.05, + 25% i.e., charcoal a > b > c. Bars represent+ 25% the meansago bark values ash.± SE. Means with different letter(s) within the same incubation period indicate significant differences between treatments according to Tukey’s HSD test at p ≤ 0.05, i.e., a > b > c. Bars represent the mean values ± SE.

Agronomy 2021, 11, 1803 11 of 28

Among the treatments, T1 had the highest soil exchangeable Fe2+ at 30, 60, and 90 DAI (Figure8). Upon application of charcoal and sago bark ash, soil exchangeable Fe 2+ Agronomy 2021, 11, x reduced. There was no signiﬁcant difference in soil exchangeable Fe2+ between11 of 28 T2 and T3, irrespective of incubation time.

FigureFigure 8. Effects 8. Effects of treatments of treatments on soil exchangeable on soil exchangeable ferrous ions ferro afterus thirty, ions sixty,after andthirty, ninety sixty, days and of ninety incubation, days where T1: soilof alone, incubation, T2: Egypt where rock T1: phosphate soil alone, alone, T2: T3: Egypt Egypt ro rockck phosphate + alone, 100% charcoal,T3: Egypt T4: rock Egypt phosphate rock phosphate + + 100% sago100% bark charcoal, ash, and T4: T5: Egypt Egypt rockrock phosphate phosphate + 100%+ 100% charcoal sago +bark 100% ash, sago and bark T5: ash, Egypt T6: Egypt rock rock phosphate phosphate + + 75% charcoal100% + 75% charcoal sago bark + 100% ash, sago T7: Egypt bark rockash, phosphateT6: Egypt +rock 50% phosphate charcoal + 75%+ 75% sago charcoal bark ash, + 75% T8: Egyptsago bark rock phosphateash, + 25%T7: charcoal Egypt + 75%rock sagophosphate bark ash, + 50% T9: Egypt charcoal rock + phosphate 75% sago + bark 75% charcoalash, T8: +Egypt 50% sagorock bark phosphate ash, T10: + Egypt25% rock phosphatecharcoal + 50% + charcoal75% sago + 50% bark sago ash, bark T9: ash, Egypt T11: rock Egypt phos rockphate phosphate + 75% + 25%charcoal charcoal + 50% + 50% sago sago bark bark ash, ash, T12:T10: Egypt rock phosphateEgypt rock + 75% phosphate charcoal + 50% 25% sagocharcoal bark ash,+ 50% T13: sago Egypt bark rock ash, phosphate T11: Egypt + 50% rock charcoal phosphate + 25% + sago 25% bark char- ash, and T14: Egyptcoal + rock 50% phosphate sago bark + ash, 25% charcoalT12: Egypt + 25% rock sago phosphat bark ash.e + Means 75% charcoal with different + 25% letter(s) sago bark within ash, the T13: same Egypt incubation periodrock indicate phosphate significant + 50% differences charcoal between + 25% sago treatments bark as accordingh, and T14: to Tukey’s Egypt HSDrock testphosphate at p ≤ 0.05, + 25% i.e., charcoal a > b > c. Bars represent+ 25% the sago mean bark values ash.± SE. Means with different letter(s) within the same incubation period indicate significant differences between treatments according to Tukey’s HSD test at p ≤ 0.05, i.e., a > b > c. Bars represent the mean valuesFigure ± SE.9 demonstrates that the application of charcoal and sago bark ash increased soil exchangeable K+. Treatment five had significantly higher soil exchangeable K+ compared with other treatments which were amended with charcoal and sago bark ash. The effects Figure 9 demonstrates that the application of charcoal and sago bark ash increased of the treatment with sago bark alone (T4) on soil exchangeable K+ was similar to those + + soil exchangeableof K T6,. Treatment T7, and T8 five at 30 had DAI significantly and T6 at 90 higher DAI. At soil 60 exchangeable and 90 DAI, soil K exchangeable com- K+ pared with other decreasedtreatments as which the rate were of sago amen barkded ash with reduced charcoal from 75%and tosago 50% bark and 25%.ash. The treatment effects of the treatmentwith charcoal with sago alone bark (T3) alone showed (T4) a low on contributionsoil exchangeable towards K soil+ was exchangeable similar to K+. those of T6, T7, and T8Exchangeable at 30 DAI and Ca2+ T6increased at 90 DAI. when At charcoal60 and 90 and DAI, sago soil bark exchangeable ash were applied to the K+ decreased as thesoil rate (Figure of sago 10). bark Treatment ash reduced one had from the lowest 75% to soil 50% exchangeable and 25%. The Ca2+ treatment. The effect of T2 on 2+ with charcoal alonesoil (T3) exchangeable showed a Ca lowwas contribution significantly towards higher comparedsoil exchangeable with T1 although K+. this treatment had no charcoal and sago bark ash. There was no significant difference in soil exchangeable Ca2+ of T2 and T3 at 60 and 90 DAI. Among the treatments with the soil amendments, the soil exchangeable Ca2+ values of T8 and T12 were higher than those of T4, T5, T6, T9, T10, T11, and T13 at 30 DAI and T13 at 90 DAI. However, at 60 DAI, the effects of the soil with charcoal and sago bark ash on exchangeable Ca2+ were similar.

Figure 9. Effects of treatments on soil exchangeable potassium ions after thirty, sixty, and ninety days of incubation, where T1: soil alone, T2: Egypt rock phosphate alone, T3: Egypt rock phosphate + 100% charcoal, T4: Egypt rock phosphate + 100% sago bark ash, and T5: Egypt rock phosphate + 100% charcoal + 100% sago bark ash, T6: Egypt rock phosphate + 75% charcoal + 75% sago bark ash, T7: Egypt rock phosphate + 50% charcoal + 75% sago bark ash, T8: Egypt rock phosphate + 25% charcoal + 75% sago bark ash, T9: Egypt rock phosphate + 75% charcoal + 50% sago bark ash, T10: Egypt rock phosphate + 50% charcoal + 50% sago bark ash, T11: Egypt rock phosphate + 25% charcoal + 50% sago bark ash, T12: Egypt rock phosphate + 75% charcoal + 25% sago bark ash, T13: Egypt rock phosphate + 50% charcoal + 25% sago bark ash, and T14: Egypt rock phosphate + 25% charcoal

Agronomy 2021, 11, x 11 of 28

Figure 8. Effects of treatments on soil exchangeable ferrous ions after thirty, sixty, and ninety days of incubation, where T1: soil alone, T2: Egypt rock phosphate alone, T3: Egypt rock phosphate + 100% charcoal, T4: Egypt rock phosphate + 100% sago bark ash, and T5: Egypt rock phosphate + 100% charcoal + 100% sago bark ash, T6: Egypt rock phosphate + 75% charcoal + 75% sago bark ash, T7: Egypt rock phosphate + 50% charcoal + 75% sago bark ash, T8: Egypt rock phosphate + 25% charcoal + 75% sago bark ash, T9: Egypt rock phosphate + 75% charcoal + 50% sago bark ash, T10: Egypt rock phosphate + 50% charcoal + 50% sago bark ash, T11: Egypt rock phosphate + 25% charcoal + 50% sago bark ash, T12: Egypt rock phosphate + 75% charcoal + 25% sago bark ash, T13: Egypt rock phosphate + 50% charcoal + 25% sago bark ash, and T14: Egypt rock phosphate + 25% charcoal + 25% sago bark ash. Means with different letter(s) within the same incubation period indicate significant differences between treatments according to Tukey’s HSD test at p ≤ 0.05, i.e., a > b > c. Bars represent the mean values ± SE.

Figure 9 demonstrates that the application of charcoal and sago bark ash increased soil exchangeable K+. Treatment five had significantly higher soil exchangeable K+ compared with other treatments which were amended with charcoal and sago bark ash. The effects of the treatment with sago bark alone (T4) on soil exchangeable K+ was similar to Agronomy 2021, 11, 1803those of T6, T7, and T8 at 30 DAI and T6 at 90 DAI. At 60 and 90 DAI, soil exchangeable 12 of 28 K+ decreased as the rate of sago bark ash reduced from 75% to 50% and 25%. The treatment with charcoal alone (T3) showed a low contribution towards soil exchangeable K+.

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+ 25% sago bark ash. Means with different letter(s) within the same incubation period indicate significant differences between treatments according to Tukey’s HSD test at p ≤ 0.05, i.e., a > b > c. Bars represent the mean values ± SE. Figure 9. EffectsFigure of treatments9. Effects of on treatments soil exchangeable on soil exchangeable potassium ions po aftertassium thirty, ions sixty, after and thirty, ninety sixty, days and of incubation, ninety where T1: soil alone,days T2: of Egypt incubation, rock phosphate where T1: alone,soil alone, T3: EgyptT2: Egyp rockt rock phosphate phosphate + 100% alone, charcoal, T3: Egypt T4: rock Egypt phosphate rock phosphate + + 100%Exchangeable charcoal, T4: Egypt Ca2+ increasedrock phosphate when + 100%charcoal sago and bark sago ash, andbark T5: ash Egypt were rock applied phosphate to the + 100% sago bark ash, and T5: Egypt rock phosphate + 100% charcoal + 100% sago bark ash, T6: Egypt rock phosphate + 75% 100%soil (Figure charcoal 10). + 100% Treatment sago bark one ash, had T6: theEgypt lowest rock phosphatesoil exchangeable + 75% charcoal Ca2+. +The 75% effect sago barkof T2 ash, on charcoal + 75% sago bark ash, T7: Egypt rock phosphate + 50% charcoal + 75% sago bark ash, T8: Egypt rock phosphate T7:soil Egypt exchangeable rock phosphate Ca2+ was + 50% significantly charcoal + higher75% sa gocompared bark ash, with T8: EgyptT1 although rock phosphate this treatment + 25% + 25% charcoal + 75% sago bark ash, T9: Egypt rock phosphate + 75% charcoal + 50% sago bark ash, T10: Egypt rock charcoalhad no charcoal+ 75% sago and bark sago ash, bark T9: Egyptash. There rock phos wasphate no significant + 75% charcoal difference + 50% insago soil bark exchangea- ash, T10: phosphate + 50% charcoal + 50% sago bark ash, T11: Egypt rock phosphate + 25% charcoal + 50% sago bark ash, T12: Egypt Egyptble Ca rock2+ of phosphate T2 and T3 + at50% 60 charcoal and 90 DAI.+ 50% Among sago bark the ash, treatments T11: Egypt with rock the phosphate soil amendments, + 25% char- rock phosphatecoal ++ 75%50% sago charcoal bark + ash, 25% T12: sago Egypt bark rock ash, T13:phosphat Egypte + rock 75% phosphate charcoal + +25% 50% sago charcoal bark ash, + 25% T13: sago Egypt bark ash, and the soil exchangeable Ca2+ values of T8 and T12 were higher than those of T4, T5, T6, T9, T14: Egypt rockrock phosphatephosphate ++ 25%50% charcoalcharcoal ++ 25% sago bark ash.ash, and Means T14: with Egypt different rock phosphate letter(s) within + 25% the charcoal same incubation T10, T11, and T13 at 30 DAI and T13 at 90 DAI. However, at 60 DAI, the effects of the soil period indicate signiﬁcant differences between treatments according to Tukey’s HSD test at p ≤ 0.05, i.e., a > b > c. Bars with charcoal and sago bark ash on exchangeable Ca2+ were similar. represent the mean values ± SE.

Figure 10. EffectsFigure of 10. treatments Effects of ontreatments soil exchangeable on soil exchangeable calcium ions calcium after thirty, ions after sixty, thirty, and ninety sixty, daysand ninety of incubation, days where T1: soil alone,of T2:incubation, Egypt rock where phosphate T1: soil alone,alone, T3:T2: EgyptEgypt rockrock phosphatephosphate +alone, 100% T3: charcoal, Egypt T4:rock Egypt phosphate rock phosphate + + 100% sago bark100% ash, charcoal, and T5: T4: Egypt Egypt rock rock phosphate phosphate + 100% + 100% charcoal sago + bark 100% ash, sago and bark T5: ash, Egypt T6: Egyptrock phosphate rock phosphate + + 75% 100% charcoal + 100% sago bark ash, T6: Egypt rock phosphate + 75% charcoal + 75% sago bark ash, charcoal + 75% sago bark ash, T7: Egypt rock phosphate + 50% charcoal + 75% sago bark ash, T8: Egypt rock phosphate T7: Egypt rock phosphate + 50% charcoal + 75% sago bark ash, T8: Egypt rock phosphate + 25% + 25% charcoal + 75% sago bark ash, T9: Egypt rock phosphate + 75% charcoal + 50% sago bark ash, T10: Egypt rock charcoal + 75% sago bark ash, T9: Egypt rock phosphate + 75% charcoal + 50% sago bark ash, T10: phosphate +Egypt 50% charcoal rock phosphate + 50% sago + 50% bark charcoal ash, T11: + Egypt50% sago rock ba phosphaterk ash, T11: + 25% Egypt charcoal rock phosphate + 50% sago + bark25% ash,char- T12: Egypt rock phosphatecoal + + 75%50% charcoalsago bark + ash, 25% T12: sago Egypt bark ash,rock T13: phosphat Egypte rock+ 75% phosphate charcoal + + 25% 50% sago charcoal bark +ash, 25% T13: sago Egypt bark ash, and T14: Egypt rockrock phosphate phosphate + +25% 50%charcoal charcoal + + 25%25% sagosago barkbark ash.ash, Meansand T14: with Egypt different rock phosphate letter(s) within + 25% the charcoal same incubation period indicate+ 25% signiﬁcant sago bark differences ash. Means between with different treatments letter(s) according within to the Tukey’s same incubation HSD test at periodp ≤ 0.05, indicate i.e., a sig- > b > c. Bars represent thenificant mean valuesdifferences± SE. between treatments according to Tukey’s HSD test at p ≤ 0.05, i.e., a > b > c. Bars represent the mean values ± SE. Soil exchangeable Mg2+ of the treatments with ERP and soil amendments (T2, T3, Soil exchangeableT4, T5, T6, Mg T7,2+ of T8, the T9, treatments T10, T11, with T12, ERP T13, and and soil T14) amendments were improved (T2, T3, compared T4, with the T5, T6, T7, T8,treatment T9, T10, T11, without T12, ERPT13, andand soilT14) amendments were improved (T1) compared (Figure 11 ).with At 30the DAI, treat- the effect of T2 ment without onERP soil and exchangeable soil amendments Mg2+ was(T1) similar(Figure to 11). those At of30 T13DAI, and the T14. effect There of T2 was on no signiﬁcant soil exchangeabledifference Mg2+ was in soil similar exchangeable to those of Mg T132+ andbetween T14. There T2 and was T3 no at 60significant and 90 DAI. dif- Additionally, ference in soil exchangeable Mg2+ between T2 and T3 at 60 and 90 DAI. Additionally, at 60 and 90 DAI, soil exchangeable Mg2+ contents increased significantly following the introduction of sago bark ash alone (T4) or combined application with charcoal (T5, T6, T7, T8, T9, T10, T11, T12, T13, and T14) compared with the treatment with charcoal alone (T3).

Agronomy 2021, 11, 1803 13 of 28

2+ Agronomy 2021, 11, x at 60 and 90 DAI, soil exchangeable Mg contents increased signiﬁcantly13 of following 28 the introduction of sago bark ash alone (T4) or combined application with charcoal (T5, T6, T7, T8, T9, T10, T11, T12, T13, and T14) compared with the treatment with charcoal alone (T3).

FigureFigure 11. Effects 11. ofEffects treatments of treatments on soil exchangeable on soil exchangeable magnesium ma ionsgnesium after thirty, ions sixty,after andthirty, ninety sixty, days and of ninety incubation, where T1:days soil of alone, incubation, T2: Egypt where rock phosphateT1: soil alone, alone, T2: T3: Egyp Egyptt rock phosphatephosphate + alone, 100% charcoal, T3: Egypt T4: rock Egypt phosphate rock phosphate + 100%+ sago 100% bark charcoal, ash, and T4: T5: Egypt Egypt rock phosphatephosphate + + 100% 100% charcoal sago bark + 100% ash, sago and bark T5: ash,Egypt T6: rock Egypt phosphate rock phosphate + + 75% charcoal100% +charcoal 75% sago + bark100% ash, sago T7: bark Egypt ash, rock T6: phosphate Egypt rock + 50% phosphate charcoal + + 75% 75% sago charcoal bark ash, + 75% T8:Egypt sago rockbarkphosphate ash, + 25% charcoalT7: Egypt + 75%rock sago phosphate bark ash, + T9:50% Egypt charcoal rock phosphate+ 75% sago + 75%bark charcoal ash, T8: + Egypt 50% sago rock bark phosphate ash, T10: + Egypt 25% rock phosphatecharcoal + 50% + charcoal 75% sago + 50% bark sago ash, bark T9: ash, Egypt T11: Egyptrock phos rock phosphatephate + 75% + 25% charcoal charcoal + +50% 50% sago sago bark bark ash,ash, T12: T10: Egypt rock phosphateEgypt rock + 75% phosphate charcoal ++ 25%50% sago charcoal bark ash,+ 50% T13: sago Egypt ba rockrk ash, phosphate T11: Egypt + 50% rock charcoal phosphate + 25% sago+ 25% bark char- ash, and T14: Egyptcoal rock+ 50% phosphate sago bark + 25% ash, charcoal T12: Egypt + 25% rock sago phosphat bark ash.e Means+ 75% withcharcoal different + 25% letter(s) sago bark within ash, the T13: same Egypt incubation periodrock indicate phosphate significant + 50% differences charcoal between + 25% treatmentssago bark accordingash, and T14: to Tukey’s Egypt HSD rock test phosphate at p ≤ 0.05, + 25% i.e., acharcoal > b > c. Bars represent+ 25% the meansago valuesbark ash.± SE. Means with different letter(s) within the same incubation period indicate significant differences between treatments according to Tukey’s HSD test at p ≤ 0.05, i.e., a > b > c. Bars represent the mean valuesThroughout ± SE. the incubation study, T1 showed the lowest soil exchangeable Na+ compared with other treatments (Figure 12). The effects of T2 and T3 on soil exchangeable Na+ Throughoutwere the incubation similar but significantlystudy, T1 showed lower than the thoselowest of T4,soil T5, exchangeable T6, T7, T8, T9, Na T10,+ com- T11, T12, T13, + pared with other andtreatments T14. There (Figure was no 12). significant The effects difference of T2 and in soil T3 exchangeableon soil exchangeable Na for the Na treatments+ with 25% sago bark ash (T12, T13, and T14), regardless of the rate of charcoal used and were similar but significantly lower than those of T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, incubation period. Although soil exchangeable Na+ decreased when the rate of sago bark + and T14. There wasash wasno significant reduced by difference 25%, with time,in soil soil exchangeable exchangeable NaNa+ increased.for the treatments with 25% sago bark ashThe (T12, interaction T13, and between T14), time regardless of incubation of the and rate treatment of charcoal significantly used and affected soil incubation period.CEC Although (Figure 13 soil). At exchangeable 30 DAI, the soil Na CEC+ decreased of T2 and when T7 were the similar rate of but sago significantly bark lower ash was reduced comparedby 25%, with with time, T5, T8, soil T9, exchangeable and T13. Although Na+ increased. T5 showed the highest soil CEC at 60 DAI, the effect was not significantly different compared to T1, T2, T3, T4, T8, T9, T10, T11, T12, and T13. At 90 DAI, soil CEC of T2 was significantly higher than those of T9, T10, T11, T12, and T13 but significantly lower compared with T3.

Figure 12. Effects of treatments on soil exchangeable sodium ions after thirty, sixty, and ninety days of incubation, where T1: soil alone, T2: Egypt rock phosphate alone, T3: Egypt rock phosphate + 100% charcoal, T4: Egypt rock phosphate + 100% sago bark ash, and T5: Egypt rock phosphate + 100% charcoal + 100% sago bark ash, T6: Egypt rock phosphate + 75% charcoal + 75% sago bark ash, T7: Egypt rock phosphate + 50% charcoal + 75% sago bark ash, T8: Egypt rock phosphate + 25% charcoal + 75% sago bark ash, T9: Egypt rock phosphate + 75% charcoal + 50% sago bark ash, T10: Egypt rock phosphate + 50% charcoal + 50% sago bark ash, T11: Egypt rock phosphate + 25% charcoal + 50% sago bark ash, T12: Egypt rock phosphate + 75% charcoal + 25% sago bark ash, T13: Egypt

Agronomy 2021, 11, x 13 of 28

Figure 11. Effects of treatments on soil exchangeable magnesium ions after thirty, sixty, and ninety days of incubation, where T1: soil alone, T2: Egypt rock phosphate alone, T3: Egypt rock phosphate + 100% charcoal, T4: Egypt rock phosphate + 100% sago bark ash, and T5: Egypt rock phosphate + 100% charcoal + 100% sago bark ash, T6: Egypt rock phosphate + 75% charcoal + 75% sago bark ash, T7: Egypt rock phosphate + 50% charcoal + 75% sago bark ash, T8: Egypt rock phosphate + 25% charcoal + 75% sago bark ash, T9: Egypt rock phosphate + 75% charcoal + 50% sago bark ash, T10: Egypt rock phosphate + 50% charcoal + 50% sago bark ash, T11: Egypt rock phosphate + 25% charcoal + 50% sago bark ash, T12: Egypt rock phosphate + 75% charcoal + 25% sago bark ash, T13: Egypt rock phosphate + 50% charcoal + 25% sago bark ash, and T14: Egypt rock phosphate + 25% charcoal + 25% sago bark ash. Means with different letter(s) within the same incubation period indicate significant differences between treatments according to Tukey’s HSD test at p ≤ 0.05, i.e., a > b > c. Bars represent the mean values ± SE.

Throughout the incubation study, T1 showed the lowest soil exchangeable Na+ compared with other treatments (Figure 12). The effects of T2 and T3 on soil exchangeable Na+ were similar but significantly lower than those of T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, and T14. There was no significant difference in soil exchangeable Na+ for the treatments with 25% sago bark ash (T12, T13, and T14), regardless of the rate of charcoal used and Agronomy 2021, 11, 1803 14 of 28 incubation period. Although soil exchangeable Na+ decreased when the rate of sago bark ash was reduced by 25%, with time, soil exchangeable Na+ increased.

Agronomy 2021, 11, x 14 of 28

rock phosphate + 50% charcoal + 25% sago bark ash, and T14: Egypt rock phosphate + 25% charcoal Figure 12. Effects+Figure 25% sago of12. treatments Effects bark ash.. of treatments on Means soil exchangeable with on different soil exchangeable sodium letter(s) ions within sodium after the thirty,ions same after sixty, incubati thirty, andon ninetysixty, period and days indicate ninety of incubation, days sig- where of incubation, where T1: soil alone, T2: Egypt rock phosphate alone, T3: Egypt rock phosphate + T1: soil alone,nificant T2: Egyptdifferences rock phosphatebetween treatments alone, T3: according Egypt rock to Tukey’s phosphate HSD + 100%test at charcoal, p ≤ 0.05, i.e., T4: a Egypt > b > c. rock Bars phosphate + represent100% charcoal, the mean T4: valuesEgypt rock± SE. phosphate + 100% sago bark ash, and T5: Egypt rock phosphate + 100% sago bark ash, and T5: Egypt rock phosphate + 100% charcoal + 100% sago bark ash, T6: Egypt rock phosphate + 75% 100% charcoal + 100% sago bark ash, T6: Egypt rock phosphate + 75% charcoal + 75% sago bark ash, charcoal + 75% sago bark ash, T7: Egypt rock phosphate + 50% charcoal + 75% sago bark ash, T8: Egypt rock phosphate T7: EgyptThe interactionrock phosphate between + 50% time charcoal of incubation + 75% sago and bark treatment ash, T8: Egypt significantly rock phosphate affected + soil25% + 25% charcoal + 75% sago bark ash, T9: Egypt rock phosphate + 75% charcoal + 50% sago bark ash, T10: Egypt rock CECcharcoal (Figure + 75% 13). sago At bark 30 DAI, ash, T9:the Egyptsoil CEC rock of phos T2 phateand T7 + 75%were charcoal similar + but 50% significantly sago bark ash, lower T10: phosphate + 50% charcoal + 50% sago bark ash, T11: Egypt rock phosphate + 25% charcoal + 50% sago bark ash, T12: Egypt comparedEgypt rock withphosphate T5, T8, + 50% T9, charcoaland T13. + Although50% sago ba T5rk showedash, T11: theEgypt highest rock phosphate soil CEC +at 25% 60 DAI,char- rock phosphatecoal + 50% 75% sago charcoal bark +ash, 25% T12: sago Egypt bark rock ash, phosphat T13: Egypte + rock 75% phosphatecharcoal + +25% 50% sago charcoal bark ash, + 25% T13: sago Egypt bark ash, and the effect was not significantly different compared to T1, T2, T3, T4, T8, T9, T10, T11, T12, T14: Egypt rock phosphate + 25% charcoal + 25% sago bark ash.. Means with different letter(s) within the same incubation and T13. At 90 DAI, soil CEC of T2 was significantly higher than those of T9, T10, T11, period indicate signiﬁcant differences between treatments according to Tukey’s HSD test at p ≤ 0.05, i.e., a > b > c. Bars T12, and T13 but significantly lower compared with T3. represent the mean values ± SE.

Figure 13. EffectsFigure of13. treatments Effects of treatments on soil cation on soil exchange cation capacityexchange after capacity thirty, after sixty, thirty, and ninetysixty, and days ninety of incubation, days where T1: soil alone,of incubation, T2: Egypt rockwhere phosphate T1: soil alone, alone, T2: T3: Egypt Egypt ro rockck phosphate phosphate alone, + 100% T3: charcoal, Egypt rock T4: Egyptphosphate rock phosphate+ + 100% charcoal, T4: Egypt rock phosphate + 100% sago bark ash, and T5: Egypt rock phosphate + 100% sago bark ash, and T5: Egypt rock phosphate + 100% charcoal + 100% sago bark ash, T6: Egypt rock phosphate + 75% 100% charcoal + 100% sago bark ash, T6: Egypt rock phosphate + 75% charcoal + 75% sago bark ash, charcoal + 75% sago bark ash, T7: Egypt rock phosphate + 50% charcoal + 75% sago bark ash, T8: Egypt rock phosphate T7: Egypt rock phosphate + 50% charcoal + 75% sago bark ash, T8: Egypt rock phosphate + 25% + 25% charcoalcharcoal + 75% + 75% sago sago bark bark ash, ash, T9: T9: Egypt Egypt rock rock phosphate phosphate + 75%+ 75% charcoal charcoal + + 50% 50% sago sago bark bark ash, ash, T10: T10: Egypt rock phosphate +Egypt 50% charcoalrock phosphate + 50% sago + 50% bark charcoal ash, T11: + 50% Egypt sago rock ba phosphaterk ash, T11: + Egypt 25% charcoal rock phosphate + 50% sago + 25% bark char- ash, T12: Egypt rock phosphatecoal + + 50% 75% sago charcoal bark +ash, 25% T12: sago Egypt bark rock ash, phosphat T13: Egypte + rock75% phosphatecharcoal + 25% + 50% sago charcoal bark ash, + 25% T13: sago Egypt bark ash, and T14: Egyptrock rock phosphate phosphate + + 50% 25% charcoal charcoal + + 25% 25% sago sago bark bark as ash.h, and Means T14: with Egypt different rock phosphate letter(s) within + 25% thecharcoal same incubation period indicate+ 25% signiﬁcant sago bark differencesash. Means between with different treatments letter(s) according within the toTukey’s same incubation HSD test period at p ≤ 0.05,indicate i.e., sig- a > b > c. Bars represent thenificant mean differences values ± SE. between treatments according to Tukey’s HSD test at p ≤ 0.05, i.e., a > b > c. Bars represent the mean values ± SE.

3.2. Effects of Amending3.2. Effects Egypt of Amending Rock Phosphate Egypt with Rock Charcoal Phosphate and with Sago Charcoal Bark Ash and on Sago Soil Bark Total Ash on Soil Total Phosphorus and PhosphorusMehlich-Phosphorus and Mehlich-Phosphorus Irrespective of Irrespectivetreatment, soil of treatment,total P increased soil total with P increased increasing with incubation increasing period incubation period (Figure 14). Treatment(Figure 14one). Treatmentshowed the one lowest showed soil thetotal lowest P compared soil total with P compared the treatments with the treatments with ERP, charcoal, and sago bark ash. At 30 DAI, soil total P of the treatment with ERP alone (T2) was significantly lower compared with T3, T5, and T12. However, this trend was not consistent throughout the incubation study. At 60 DAI, the soil total P of T6, T11, and T14 were similar but significantly higher than those of T2, T3, and T12. Towards the end of the incubation study (90 DAI), the soil total P values of the treatments were not significantly different except for T1. The treatment with charcoal alone (T3) demonstrated lower soil total P at 60 and 90 DAI compared with 30 DAI.

Agronomy 2021, 11, 1803 15 of 28

with ERP, charcoal, and sago bark ash. At 30 DAI, soil total P of the treatment with ERP alone (T2) was significantly lower compared with T3, T5, and T12. However, this trend was not consistent throughout the incubation study. At 60 DAI, the soil total P of T6, T11, and T14 were similar but significantly higher than those of T2, T3, and T12. Towards the end of the incubation study (90 DAI), the soil total P values of the treatments were not Agronomy 2021, 11, x 15 of 28 significantly different except for T1. The treatment with charcoal alone (T3) demonstrated lower soil total P at 60 and 90 DAI compared with 30 DAI.

Figure 14. EffectsFigure of 14. treatments Effects of on treatments soil total on phosphorus soil total phosphorus after thirty, after sixty, thirty, and ninety sixty, daysand ninety of incubation, days of incu- where T1: soil alone, T2: Egyptbation, rock where phosphate T1: soil alone, alone, T3: T2: Egypt Egypt rock rock phosphate phosphate + 100% alone, charcoal, T3: Egypt T4: Egypt rock rockphosphate phosphate + 100% + 100% sago bark ash, andcharcoal, T5: Egypt T4: rock Egypt phosphate rock phosphate + 100% charcoal + 100% +sago 100% bark sago ash, bark and ash, T5: T6: Egypt Egypt rock rock phosphate phosphate + + 100% 75% charcoal + charcoal + 100% sago bark ash, T6: Egypt rock phosphate + 75% charcoal + 75% sago bark ash, T7: 75% sago bark ash, T7: Egypt rock phosphate + 50% charcoal + 75% sago bark ash, T8: Egypt rock phosphate + 25% charcoal Egypt rock phosphate + 50% charcoal + 75% sago bark ash, T8: Egypt rock phosphate + 25% charcoal + 75% sago bark ash, T9: Egypt rock phosphate + 75% charcoal + 50% sago bark ash, T10: Egypt rock phosphate + 50% + 75% sago bark ash, T9: Egypt rock phosphate + 75% charcoal + 50% sago bark ash, T10: Egypt rock charcoal + 50%phosphate sago bark + ash,50% T11:charcoal Egypt + rock50% phosphatesago bark +ash, 25% T11: charcoal Egypt + rock 50% phosphate sago bark ash, + 25% T12: charcoal Egypt rock + 50% phosphate + 75% charcoalsago + 25% bark sago ash, bark T12: ash, Egypt T13: rock Egypt phosphate rock phosphate + 75% +charcoal 50% charcoal + 25% +sago 25% bark sago ash, bark T13: ash, Egypt and T14: rock Egypt rock phosphate +phosphate 25% charcoal + 50% + 25% charcoal sago bark + 25% ash. sago Means bark with ash, different and T14: letter(s) Egypt withinrock phosphate the same + incubation 25% charcoal period + indicate significant differences25% sago betweenbark ash. treatments Means with according different to letter(s) Tukey’s within HSD testthe atsamep ≤ incubation0.05, i.e., a >period b > c. indicate Bars represent signif- the mean values ± SE.icant differences between treatments according to Tukey’s HSD test at p ≤ 0.05, i.e., a > b > c. Bars represent the mean values ± SE. Soil Mehlich-P demonstrated a different trend compared with soil total P (Figure 15). Soil Mehlich-PRegardless demonstrated of incubation a different period, tren soild Mehlich-P compared of with T1 was soil thetotal lowest P (Figure among 15). the treatments. Regardless ofThe incubation effects of period, the treatments soil Mehlich-P with ERP, of T1 charcoal, was the and lowest sago barkamong ash the (T2, treat- T3, T4, T5, T6, T7, ments. The effectsT8, T9, of the T10, treatments T11, T12, T13,with andERP, T14) charcoal, on soil and Mehlich-P sago bark were ash higher(T2, T3, at T4, 30 T5, DAI, decreased T6, T7, T8, T9,at T10, 60 DAI, T11, andT12, recoveredT13, and T14) at 90 on DAI. soil At Mehlich-P 30 DAI, therewere washigher no significantat 30 DAI, differencede- in soil creased at 60 DAI,Mehlich-P and recovered between at T2 90 and DAI. the At treatments 30 DAI, there with was ERP, no significant charcoal, and difference sago bark ash. Soil in soil Mehlich-PMehlich-P between of T2 and was the significantly treatments lower with than ERP, those charcoal, of T9 and and sago T11 butbark significantly ash. higher Soil Mehlich-Pcompared of T2 was with significantly T3 at 60 DAI. lower At 90 than DAI, those the effects of T9 ofand T2, T11 T6, but T12, significantly and T13 on soil Mehlich-P higher comparedwere with similar T3 at but 60 higher DAI. At than 90 thoseDAI, the of T3, effects T5,and of T2, T7. T6, T12, and T13 on soil Mehlich-P were similar but higher than those of T3, T5, and T7. 3.3. Effects of Amending Egypt Rock Phosphate with Charcoal and Sago Bark Ash on Soil Inorganic Phosphorus Fractions Figure 16 demonstrates that Sol-P increased following the addition of P to the soil. However, application of ERP alone (T2) had lower Sol-P compared with T5, T6, and T13 at 30 DAI, T4 and T5 at 60 DAI, and T4, T5, T6, T7, T8, and T11 at 90 DAI. Although T3 and T4 represents charcoal alone and sago bark ash alone, their effects on Sol-P were similar to those of the soil with both charcoal and sago bark ash, irrespective of incubation time. It was noticed that, at 90 DAI, the Sol-P fraction was slightly lower than at 60 DAI.

Figure 15. Effects of treatments on soil Mehlich-phosphorus after thirty, sixty, and ninety days of incubation, where T1: soil alone, T2: Egypt rock phosphate alone, T3: Egypt rock phosphate + 100% charcoal, T4: Egypt rock phosphate + 100% sago bark ash, and T5: Egypt rock phosphate + 100% charcoal + 100% sago bark ash, T6: Egypt rock phosphate + 75% charcoal + 75% sago bark ash, T7: Egypt rock phosphate + 50% charcoal + 75% sago bark ash, T8: Egypt rock phosphate + 25% charcoal

Agronomy 2021, 11, x 15 of 28

Figure 14. Effects of treatments on soil total phosphorus after thirty, sixty, and ninety days of incubation, where T1: soil alone, T2: Egypt rock phosphate alone, T3: Egypt rock phosphate + 100% charcoal, T4: Egypt rock phosphate + 100% sago bark ash, and T5: Egypt rock phosphate + 100% charcoal + 100% sago bark ash, T6: Egypt rock phosphate + 75% charcoal + 75% sago bark ash, T7: Egypt rock phosphate + 50% charcoal + 75% sago bark ash, T8: Egypt rock phosphate + 25% charcoal + 75% sago bark ash, T9: Egypt rock phosphate + 75% charcoal + 50% sago bark ash, T10: Egypt rock phosphate + 50% charcoal + 50% sago bark ash, T11: Egypt rock phosphate + 25% charcoal + 50% sago bark ash, T12: Egypt rock phosphate + 75% charcoal + 25% sago bark ash, T13: Egypt rock phosphate + 50% charcoal + 25% sago bark ash, and T14: Egypt rock phosphate + 25% charcoal + 25% sago bark ash. Means with different letter(s) within the same incubation period indicate significant differences between treatments according to Tukey’s HSD test at p ≤ 0.05, i.e., a > b > c. Bars represent the mean values ± SE.

Soil Mehlich-P demonstrated a different trend compared with soil total P (Figure 15). Regardless of incubation period, soil Mehlich-P of T1 was the lowest among the treatments. The effects of the treatments with ERP, charcoal, and sago bark ash (T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, and T14) on soil Mehlich-P were higher at 30 DAI, decreased at 60 DAI, and recovered at 90 DAI. At 30 DAI, there was no significant difference in soil Mehlich-P between T2 and the treatments with ERP, charcoal, and sago bark ash. Soil Mehlich-P of T2 was significantly lower than those of T9 and T11 but significantly Agronomy 2021higher, 11, 1803 compared with T3 at 60 DAI. At 90 DAI, the effects of T2, T6, T12, and T13 on soil 16 of 28 Agronomy 2021, 11, x 16 of 28 Mehlich-P were similar but higher than those of T3, T5, and T7.

+ 75% sago bark ash, T9: Egypt rock phosphate + 75% charcoal + 50% sago bark ash, T10: Egypt rock phosphate + 50% charcoal + 50% sago bark ash, T11: Egypt rock phosphate + 25% charcoal + 50% sago bark ash, T12: Egypt rock phosphate + 75% charcoal + 25% sago bark ash, T13: Egypt rock phosphate + 50% charcoal + 25% sago bark ash, and T14: Egypt rock phosphate + 25% charcoal + 25% sago bark ash. Means with different letter(s) within the same incubation period indicate significant differences between treatments according to Tukey’s HSD test at p ≤ 0.05, i.e., a > b > c. Bars represent the mean values ± SE.

3.3. Effects of Amending Egypt Rock Phosphate with Charcoal and Sago Bark Ash on Soil Inorganic Phosphorus Fractions Figure 16 demonstrates that Sol-P increased following the addition of P to the soil. However, application of ERP alone (T2) had lower Sol-P compared with T5, T6, and T13 at 30 DAI, T4 and T5 at 60 DAI, and T4, T5, T6, T7, T8, and T11 at 90 DAI. Although T3 FigureFigure 15.andEffects T4 15. represents of Effects treatments of treatmentscharcoal on soil Mehlich-phosphorus alone on soil and Mehlich-phosphor sago afterbark thirty, ash alone, sixty,us after and their thirty, ninety effects dayssixty, ofon and incubation, Sol-P ninety were wheredays sim- of T1: soil alone, T2:incubation,ilar Egypt to those rock where phosphate of the T1: soil alone, alone,with T3: EgyptbothT2: Egypt rockcharcoal phosphaterock phosphateand+ sago 100% alone,bark charcoal, ash,T3: T4:Egypt irrespective Egypt rock rock phosphate phosphate of incubation + + 100% 100% sago bark ash,charcoal,time. and T5:It was EgyptT4: Egypt noticed rock phosphaterock that, phosphate at + 100%90 DAI, charcoal+ 100% the sago +Sol-P 100% bark fraction sago ash, bark andwas ash, T5: T6:slightly Egypt rocklowerrock phosphate phosphate than at + 60 75% + DAI.100% charcoal + 75% sagocharcoal barkThe ash, + result T7:100% Egypt sago in rockFigure bark phosphate ash, 17 demonstratesT6: + Egypt 50% charcoal rock thatph + 75%osphate the sago addition bark+ 75% ash, charcoal of T8: ERP Egypt increased+ 75% rock phosphatesago the bark Al-P + ash, 25% frac- T7: charcoal + 75% sagoEgypttion. bark Aluminium-boundrock ash, phosphate T9: Egypt + rock 50% phosphate Pcharcoal for the ++ treatment75% 75% sago charcoal ba withrk + ash, 50% ERP T8: sago aloneEgypt bark ash,(T2)rock T10: phosphatewas Egypt significantly rock + 25% phosphate charcoal lower + 50% charcoalcompared + 50% sago barkwith ash, T4 T11: and Egypt T11 rock at 30 phosphate DAI. However, + 25% charcoal at 60 + 50% DAI, sago the bark effect ash, T12: of T2 Egypt on rockAl-P phosphate was + 75% charcoalsignificantly + 25% sago higher bark ash, than T13: those Egypt of rock T3, phosphate T6, T7, T9, + 50% T12, charcoal and T13 + 25% at sago60 DAI. bark Additionally, ash, and T14: Egypt the rock phosphate + 25% charcoal + 25% sago bark ash. Means with different letter(s) within the same incubation period indicate increase in Al-P of T2 was detected at 90 DAI, where T2 had higher Al-P compared with signiﬁcant differences between treatments according to Tukey’s HSD test at p ≤ 0.05, i.e., a > b > c. Bars represent the mean values ±T3,SE. T5, T6, T7, T8, T9, T10, T11, T12, T13, and T14.

Figure 16.FigureEffects 16. of Effects treatments of treatments on loosely solubleon loosely phosphorus soluble phosph after thirty,orus sixty, after and thirty, ninety sixty, days and of incubation, ninety days where of T1: soil alone,incubation, T2: Egypt where rock phosphate T1: soil alone, alone, T3:T2: EgyptEgypt rock rock phosphate phosphate + 100%alone, charcoal, T3: Egypt T4: Egyptrock phosphate rock phosphate + 100% + 100% sago barkcharcoal, ash, and T4: T5: Egypt Egypt rock rock phosphate + + 100% 100% charcoal sago bark + 100% ash, sago and bark T5: ash,Egypt T6: rock Egypt phosphate rock phosphate + 100% + 75% charcoalcharcoal + 75% sago + 100% bark ash,sago T7: bark Egypt ash, rock T6: phosphateEgypt rock + 50%phosphate charcoal + +75% 75% charcoal sago bark + ash, 75% T8: sago Egypt bark rock ash, phosphate T7: + 25% charcoalEgypt rock + 75% phosphate sago bark + ash,50% T9: charcoal Egypt + rock 75% phosphate sago bark + ash, 75% T8: charcoal Egypt + rock 50% phosphate sago barkash, + 25% T10: charcoal Egypt rock phosphate+ 75% + 50% sago charcoal bark ash, + 50% T9: sago Egypt bark rock ash, T11:phosphate Egypt rock + 75% phosphate charcoal + 25%+ 50% charcoal sago bark + 50% ash, sago T10: bark Egypt ash, T12: rock Egypt rock phosphatephosphate + 75% + 50% charcoal charcoal + 25% + sago 50% bark sago ash, bark T13: ash, Egypt T11: rock Egypt phosphate rock +phosphate 50% charcoal + 25% + 25% charcoal sago bark + 50% ash, and T14: Egyptsago rock bark phosphate ash, T12: + 25% Egypt charcoal rock +phosphate 25% sago bark + 75% ash. charcoal Means with + 25% different sago letter(s) bark ash, within T13: the Egypt same incubation rock period indicatephosphate signiﬁcant + 50% differencescharcoal + between25% sago treatments bark ash, according and T14: to Egypt Tukey’s rock HSD phosphate test at p ≤ 0.05,+ 25% i.e., charcoal a > b > c. + Bars represent25% the sago mean bark values ash.± SE.Means with different letter(s) within the same incubation period indicate significant differences between treatments according to Tukey’s HSD test at p ≤ 0.05, i.e., a > b > c. Bars represent the mean valuesThe ± result SE. in Figure 17 demonstrates that the addition of ERP increased the Al-P fraction. Aluminium-bound P for the treatment with ERP alone (T2) was signiﬁcantly

Agronomy 2021, 11, 1803 17 of 28

lower compared with T4 and T11 at 30 DAI. However, at 60 DAI, the effect of T2 on Al-P Agronomy 2021, 11, x was signiﬁcantly higher than those of T3, T6, T7, T9, T12, and T13 at 60 DAI. Additionally,17 of 28

the increase in Al-P of T2 was detected at 90 DAI, where T2 had higher Al-P compared with T3, T5, T6, T7, T8, T9, T10, T11, T12, T13, and T14.

FigureFigure 17. Effects 17. Effects of treatments of treatments on aluminium-bound on aluminium-bound phosphorus afterphosphorus thirty, sixty, after and thirty, ninety dayssixty, of and incubation, ninety where days T1:of soil incubation, alone, T2: Egypt where rock T1: phosphate soil alone, alone, T2: T3: Egypt Egypt rockrock phosphate phosphate + 100% alone, charcoal, T3: Egypt T4: Egypt rock rock phosphate phosphate ++ 100%100% sago charcoal, bark ash, and T4: T5: Egypt Egypt rock phosphate phosphate + 100% + 100% charcoal sago + 100% bark sago ash, bark and ash, T5: T6: Egypt Egypt rockrock phosphate phosphate + 75% + charcoal100% + charcoal 75% sago + bark 100% ash, sago T7: Egypt bark rockash, phosphate T6: Egypt + 50%rock charcoal phosphate + 75% +sago 75% bark charcoal ash, T8: + Egypt75% sago rock phosphatebark ash, + 25% charcoal + 75% sago bark ash, T9: Egypt rock phosphate + 75% charcoal + 50% sago bark ash, T10: Egypt rock T7: Egypt rock phosphate + 50% charcoal + 75% sago bark ash, T8: Egypt rock phosphate + 25% phosphate + 50% charcoal + 50% sago bark ash, T11: Egypt rock phosphate + 25% charcoal + 50% sago bark ash, T12: Egypt charcoal + 75% sago bark ash, T9: Egypt rock phosphate + 75% charcoal + 50% sago bark ash, T10: rock phosphate + 75% charcoal + 25% sago bark ash, T13: Egypt rock phosphate + 50% charcoal + 25% sago bark ash, and T14:Egypt Egypt rock rock phosphatephosphate + 25% + 50% charcoal charcoal + 25% + sago 50% bark sago ash. ba Meansrk ash, with T11: different Egypt letter(s) rock withinphosphate the same + 25% incubation char- periodcoal indicate + 50% sago significant bark differences ash, T12: betweenEgypt rock treatments phosphat accordinge + 75% to Tukey’scharcoal HSD + 25% test atsagop ≤ 0.05,bark i.e., ash, a >T13: b > c.Egypt Bars representrock phosphate the mean values + 50%± SE. charcoal + 25% sago bark ash, and T14: Egypt rock phosphate + 25% charcoal + 25% sago bark ash. Means with different letter(s) within the same incubation period indicate significant differences betweenAn treatments appreciable according amount of to P Tukey’s was also HSD fixed test by at Fe p (Figure ≤ 0.05, 18i.e.,). a Regardless > b > c. Bars of the represent the mean valuesincubation ± SE. period, T1 demonstrated a lower Fe-P fraction compared with the treatments with ERP. There was no significant difference in Fe-P for T2 and T4, T7, T8, and T14 at 30 DAI, T8 at 60 DAI, and T11 at 90 DAI. Iron-bound P for the treatments with charcoal An appreciableand amount sago bark of ash P was decreased also fixed at 90 DAI. by Fe (Figure 18). Regardless of the incubation period, T1 demonstratedRegardless ofa lower treatment, Fe-P the fr fixationaction ofcompared P as Red-P with was not the consistent treatments throughout with the ERP. There was noincubation significant study difference (Figure 19 in). Fe-P With for time, T2 T9, and T10, T4, and T7, T11 T8, increased and T14 the at Red-P 30 DAI, fraction, T8 at 60 DAI, and T11whereas at 90 fluctuation DAI. Iron-bound was noticed P for for other the treatments. treatments At 30with DAI, charcoal the effect and of T2 sago on Red-P fraction was similar to T3 and T5 but significantly higher than those of T4, T6, T7, T8, T9, bark ash decreased at 90 DAI. T10, T11, T12, T13, and T14. Reductant soluble P of T2 was significantly higher compared with T8, T9, and T11 at 60 DAI, and T11 at 90 DAI.

Figure 18. Effects of treatments on iron-bound phosphorus after thirty, sixty, and ninety days of incubation, where T1: soil alone, T2: Egypt rock phosphate alone, T3: Egypt rock phosphate + 100% charcoal, T4: Egypt rock phosphate + 100% sago bark ash, and T5: Egypt rock phosphate + 100% charcoal + 100% sago bark ash, T6: Egypt rock phosphate + 75% charcoal + 75% sago bark ash, T7: Egypt rock phosphate + 50% charcoal + 75% sago bark ash, T8: Egypt rock phosphate + 25% charcoal + 75% sago bark ash, T9: Egypt rock phosphate + 75% charcoal + 50% sago bark ash, T10: Egypt rock phosphate + 50% charcoal + 50% sago bark ash, T11: Egypt rock phosphate + 25% charcoal + 50% sago bark ash, T12: Egypt rock phosphate + 75% charcoal + 25% sago bark ash, T13: Egypt rock phosphate + 50% charcoal + 25% sago bark ash, and T14: Egypt rock phosphate + 25% charcoal +

Agronomy 2021, 11, x 17 of 28

Figure 17. Effects of treatments on aluminium-bound phosphorus after thirty, sixty, and ninety days of incubation, where T1: soil alone, T2: Egypt rock phosphate alone, T3: Egypt rock phosphate + 100% charcoal, T4: Egypt rock phosphate + 100% sago bark ash, and T5: Egypt rock phosphate + 100% charcoal + 100% sago bark ash, T6: Egypt rock phosphate + 75% charcoal + 75% sago bark ash, T7: Egypt rock phosphate + 50% charcoal + 75% sago bark ash, T8: Egypt rock phosphate + 25% charcoal + 75% sago bark ash, T9: Egypt rock phosphate + 75% charcoal + 50% sago bark ash, T10: Egypt rock phosphate + 50% charcoal + 50% sago bark ash, T11: Egypt rock phosphate + 25% charcoal + 50% sago bark ash, T12: Egypt rock phosphate + 75% charcoal + 25% sago bark ash, T13: Egypt rock phosphate + 50% charcoal + 25% sago bark ash, and T14: Egypt rock phosphate + 25% charcoal + 25% sago bark ash. Means with different letter(s) within the same incubation period indicate significant differences between treatments according to Tukey’s HSD test at p ≤ 0.05, i.e., a > b > c. Bars represent the mean values ± SE.

An appreciable amount of P was also fixed by Fe (Figure 18). Regardless of the incubation period, T1 demonstrated a lower Fe-P fraction compared with the treatments with Agronomy 2021, 11, 1803ERP. There was no significant difference in Fe-P for T2 and T4, T7, T8, and T14 at 30 DAI, 18 of 28 T8 at 60 DAI, and T11 at 90 DAI. Iron-bound P for the treatments with charcoal and sago bark ash decreased at 90 DAI.

Agronomy 2021, 11, x 18 of 28

Figure 18. Effects25%Figure sago of 18. treatments bark Effects ash. of Means on treatments iron-bound with different on phosphorus iron -boundletter(s) after phosphorus within thirty, the sixty, same after and incubation thirty ninety, sixty, days period and ofincubation, indicateninety days signif- where of T1: soil alone, T2: Egypticantincubation, rockdifferences phosphate where between T1: alone, soil treatmentsalone, T3: Egypt T2: Egypt rockaccordingphosphate rock phosphateto Tukey’s + 100% alone,HSD charcoal, test T3: atEgypt T4: p ≤ Egypt 0.05,rock i.e., rockphosphate aphosphate > b > +c. 100% Bars + 100% sago bark ash, andrepresentcharcoal, T5: Egypt T4:the rock Egyptmean phosphate valuesrock phosphate ± +SE. 100% charcoal + 100% +sago 100% bark sago ash, bark and ash, T5: T6: Egypt Egypt rock rock phosphate phosphate + +100% 75% charcoal + 75% sago barkcharcoal ash, T7: + Egypt100% sago rock phosphatebark ash, T6: + 50% Egypt charcoal rock ph + 75%osphate sago + bark 75% ash,charcoal T8: Egypt + 75% rock sago phosphate bark ash, + T7: 25% charcoal Egypt rock phosphate + 50% charcoal + 75% sago bark ash, T8: Egypt rock phosphate + 25% charcoal + 75% sago bark ash,Regardless T9: Egypt of rocktreatment, phosphate the fixation + 75% charcoal of P as + Red-P 50% sago was bark not ash,consistent T10: Egypt throughout rock phosphate the + 50% + 75% sago bark ash, T9: Egypt rock phosphate + 75% charcoal + 50% sago bark ash, T10: Egypt rock charcoal + 50%incubation sago bark study ash, T11: (Figure Egypt 19). rock With phosphate time, + T9 25%, T10, charcoal and + T11 50% increased sago bark ash,the T12:Red-P Egypt fraction, rock phosphate + phosphate + 50% charcoal + 50% sago bark ash, T11: Egypt rock phosphate + 25% charcoal + 50% 75% charcoalwhereassago + 25% bark sago fluctuation ash, bark T12: ash, Egypt was T13: rocknoticed Egypt phosphate rock for phosphateother + 75% treatm charcoal + 50%ents. charcoal +At 25% 30 DAI, +sago 25% barkthe sago effect ash, bark T13: of ash, T2 Egypt and on T14:Red- rock Egypt rock phosphate +Pphosphate 25% fraction charcoal +was 50% + 25%similar charcoal sago to bark+ T3 25% ash.and sago MeansT5 bark but with ash,significantly differentand T14: letter(s) Egypthigher rock within than phosphate those the same of + incubationT4, 25% T6, charcoal T7, period T8, + indicate signiﬁcant differencesT9, T10, T11, between T12, treatments T13, and accordingT14. Reductant to Tukey’s soluble HSD testP of at T2p ≤ was0.05, significantly i.e., a > b > c. higher Bars represent com- the mean values ± SE.pared with T8, T9, and T11 at 60 DAI, and T11 at 90 DAI.

Figure 19. EffectsFigure of 19. treatments Effects of ontreatments reductant on soluble reductant phosphorus soluble phos afterphorus thirty, after sixty, thirty, and ninety sixty, and days ninety of incubation, days where T1: soil alone,of incubation, T2: Egypt rock where phosphate T1: soil alone, T3:T2: Egypt rockrock phosphatephosphate +alone, 100% T3: charcoal, Egypt T4:rock Egypt phosphate rock phosphate+ + 100% charcoal, T4: Egypt rock phosphate + 100% sago bark ash, and T5: Egypt rock phosphate + 100% sago bark ash, and T5: Egypt rock phosphate + 100% charcoal + 100% sago bark ash, T6: Egypt rock phosphate + 75% 100% charcoal + 100% sago bark ash, T6: Egypt rock phosphate + 75% charcoal + 75% sago bark ash, charcoal + 75% sago bark ash, T7: Egypt rock phosphate + 50% charcoal + 75% sago bark ash, T8: Egypt rock phosphate T7: Egypt rock phosphate + 50% charcoal + 75% sago bark ash, T8: Egypt rock phosphate + 25% + 25% charcoalcharcoal + 75% + 75% sago sago bark bark ash, ash, T9: EgyptT9: Egypt rock rock phosphate phosphate + 75% + 75% charcoal charcoal + 50%+ 50% sago sago bark bark ash, ash, T10: T10: Egypt rock phosphate +Egypt 50% charcoal rock phosphate + 50% sago + 50% bark charcoal ash, T11: + 50% Egypt sago rock ba phosphaterk ash, T11: + 25%Egypt charcoal rock phosphate + 50% sago + bark25% char- ash, T12: Egypt rock phosphatecoal ++ 75%50% sago charcoal bark + ash, 25% T12: sago Egypt bark rock ash, T13:phosphat Egypte + rock 75% phosphate charcoal + +25% 50% sago charcoal bark ash, + 25% T13: sago Egypt bark ash, and T14: Egypt rockrock phosphatephosphate ++ 25%50% charcoalcharcoal ++ 25% sago bark ash.ash, and Means T14: with Egypt different rock phosphate letter(s) within + 25% the charcoal same incubation period indicate+ 25% signiﬁcant sago bark differences ash. Means between with different treatments letter(s) according within tothe Tukey’s same incubation HSD test atperiodp ≤ 0.05, indicate i.e., asig- > b > c. Bars represent thenificant mean valuesdifferences± SE. between treatments according to Tukey’s HSD test at p ≤ 0.05, i.e., a > b > c. Bars represent the mean values ± SE.

The results further reveal that Ca-P increased with the application of ERP (Figure 20). There were no significant differences in Ca-P for the soil with ERP alone (T2) and soil with charcoal and sago bark ash at 30, 60, and 90 DAI.

Figure 20. Effects of treatments on calcium-bound phosphorus after thirty, sixty, and ninety days of incubation, where T1: soil alone, T2: Egypt rock phosphate alone, T3: Egypt rock phosphate + 100%

Agronomy 2021, 11, x 18 of 28

25% sago bark ash. Means with different letter(s) within the same incubation period indicate significant differences between treatments according to Tukey’s HSD test at p ≤ 0.05, i.e., a > b > c. Bars represent the mean values ± SE.

Regardless of treatment, the fixation of P as Red-P was not consistent throughout the incubation study (Figure 19). With time, T9, T10, and T11 increased the Red-P fraction, whereas fluctuation was noticed for other treatments. At 30 DAI, the effect of T2 on Red- P fraction was similar to T3 and T5 but significantly higher than those of T4, T6, T7, T8, T9, T10, T11, T12, T13, and T14. Reductant soluble P of T2 was significantly higher compared with T8, T9, and T11 at 60 DAI, and T11 at 90 DAI.

Figure 19. Effects of treatments on reductant soluble phosphorus after thirty, sixty, and ninety days of incubation, where T1: soil alone, T2: Egypt rock phosphate alone, T3: Egypt rock phosphate + 100% charcoal, T4: Egypt rock phosphate + 100% sago bark ash, and T5: Egypt rock phosphate + 100% charcoal + 100% sago bark ash, T6: Egypt rock phosphate + 75% charcoal + 75% sago bark ash, T7: Egypt rock phosphate + 50% charcoal + 75% sago bark ash, T8: Egypt rock phosphate + 25% charcoal + 75% sago bark ash, T9: Egypt rock phosphate + 75% charcoal + 50% sago bark ash, T10: Egypt rock phosphate + 50% charcoal + 50% sago bark ash, T11: Egypt rock phosphate + 25% charcoal + 50% sago bark ash, T12: Egypt rock phosphate + 75% charcoal + 25% sago bark ash, T13: Egypt rock phosphate + 50% charcoal + 25% sago bark ash, and T14: Egypt rock phosphate + 25% charcoal + 25% sago bark ash. Means with different letter(s) within the same incubation period indicate sig- Agronomynificant2021, 11, 1803differences between treatments according to Tukey’s HSD test at p ≤ 0.05, i.e., a > b > c. Bars19 of 28 represent the mean values ± SE.

The results furtherThe reveal results that further Ca-P reveal increased that Ca-P with increased the application with the application of ERP (Figure of ERP (Figure 20). 20). There were no significantThere were differences no signiﬁcant in Ca-P differences for the in Ca-Psoil with for the ERP soil withalone ERP (T2) alone and (T2) soil and with soil with charcoal and sago barkcharcoal ash and at sago30, 60, bark and ash 90 at 30,DAI. 60, and 90 DAI.

FigureFigure 20. Effects20. Effects of treatments of treatments on calcium-bound on calcium-bound phosphorus phosphor after thirty,us sixty, after and thirty, ninety dayssixty, of and incubation, ninety where days T1:of soilincubation, alone, T2: Egypt where rock T1: phosphate soil alone, alone, T2: T3: Egypt Egypt rock phosphate phosphate + 100% alone, charcoal, T3: Egypt T4: Egypt rock rock phosphate phosphate + + 100% 100% sago bark ash, and T5: Egypt rock phosphate + 100% charcoal + 100% sago bark ash, T6: Egypt rock phosphate + 75% charcoal + 75% sago bark ash, T7: Egypt rock phosphate + 50% charcoal + 75% sago bark ash, T8: Egypt rock phosphate + 25% charcoal + 75% sago bark ash, T9: Egypt rock phosphate + 75% charcoal + 50% sago bark ash, T10: Egypt rock phosphate + 50% charcoal + 50% sago bark ash, T11: Egypt rock phosphate + 25% charcoal + 50% sago bark ash, T12: Egypt rock phosphate + 75% charcoal + 25% sago bark ash, T13: Egypt rock phosphate + 50% charcoal + 25% sago bark ash, and T14: Egypt rock phosphate + 25% charcoal + 25% sago bark ash. Means with different letter(s) within the same incubation period indicate signiﬁcant differences between treatments according to Tukey’s HSD test at p ≤ 0.05, i.e., a > b > c. Bars represent the mean values ± SE.

At 30 DAI, Occl-P of T11 was higher than those of T2, T3, T4, T5, T6, T7, T8, T9, T10, and T12 (Figure 21). However, the trend changed at 60 DAI, where T3 was signiﬁcantly higher compared with T2, T4, T7, T9, T10, T11, T12, T13, and T14. Regardless of treatment, Occl-P fraction was uniform towards the end of incubation study (90 DAI), with almost all treatments with ERP making no signiﬁcant difference.

3.4. Percentages of Soil Inorganic Phosphorus Distribution by Treatment after Thirty, Sixty, and Ninety Days of Incubation The initial inorganic P speciation of the soil used in this present study was in the order of Fe-P (67%) > Occl-P (12%) > Al-P (11%) > Ca-P (7%) > Red-P (3%) > Sol-P (Table2). Although the order differed from that recorded in a study carried out by Has- bullah et al. [78]—Fe-P (68%) > Al-P (13%) > Red-P (10%) > Occl-P (7%) > Ca-P (2%) > Sol-P—both ﬁndings are consistent with that reported by Bidin [79], who mentioned that Fe-P is dominant in Malaysian soils, with an average of 79%. Agronomy 2021, 11, x 19 of 28

charcoal, T4: Egypt rock phosphate + 100% sago bark ash, and T5: Egypt rock phosphate + 100% charcoal + 100% sago bark ash, T6: Egypt rock phosphate + 75% charcoal + 75% sago bark ash, T7: Egypt rock phosphate + 50% charcoal + 75% sago bark ash, T8: Egypt rock phosphate + 25% charcoal + 75% sago bark ash, T9: Egypt rock phosphate + 75% charcoal + 50% sago bark ash, T10: Egypt rock phosphate + 50% charcoal + 50% sago bark ash, T11: Egypt rock phosphate + 25% charcoal + 50% sago bark ash, T12: Egypt rock phosphate + 75% charcoal + 25% sago bark ash, T13: Egypt rock phosphate + 50% charcoal + 25% sago bark ash, and T14: Egypt rock phosphate + 25% charcoal + 25% sago bark ash. Means with different letter(s) within the same incubation period indicate significant differences between treatments according to Tukey’s HSD test at p ≤ 0.05, i.e., a > b > c. Bars represent the mean values ± SE.

At 30 DAI, Occl-P of T11 was higher than those of T2, T3, T4, T5, T6, T7, T8, T9, T10, and T12 (Figure 21). However, the trend changed at 60 DAI, where T3 was significantly higher compared with T2, T4, T7, T9, T10, T11, T12, T13, and T14. Regardless of treatment, Agronomy 2021, 11, 1803 20 of 28 Occl-P fraction was uniform towards the end of incubation study (90 DAI), with almost all treatments with ERP making no significant difference.

FigureFigure 21. Effects21. Effects of treatments of treatments on occluded on occluded phosphorus phosphorus after thirty, sixty, after and thirty, ninety sixty, days ofand incubation, ninety days where of T1: incu- soil alone,bation, T2: Egypt where rock T1: phosphate soil alone, alone, T2: T3: EgyptEgypt rock rock phosphate phosphate + 100% alone, charcoal, T3: T4: Egypt Egypt rock phosphate phosphate + 100% + 100% sago barkcharcoal, ash, and T5:T4: Egypt Egypt rock rock phosphate phosphate + 100% + charcoal 100% sago + 100% bark sago ash, bark ash,and T6: T5: Egypt Egypt rock rock phosphate phosphate + 75% charcoal + 100% + 75%charcoal sago bark + ash, 100% T7: Egyptsago rockbark phosphate ash, T6: +Egypt 50% charcoal rock ph + 75%osphate sago bark + 75% ash, T8:charcoal Egypt rock+ 75% phosphate sago bark + 25% ash, charcoal T7: + 75%Egypt sago rock bark phosphate ash, T9: Egypt + 50% rock charcoal phosphate + + 75% 75% sago charcoal bark + 50%ash, sago T8: barkEgypt ash, rock T10: phosphate Egypt rock phosphate+ 25% charcoal + 50% charcoal+ 75% + sago 50% sago bark bark ash, ash, T9: T11: Egypt Egypt rock rock phosphate + 25%+ 75% charcoal charcoal + 50% +sago 50% bark sago ash, bark T12: ash, Egypt T10: rock Egypt phosphate rock + 75%phosphate charcoal + 25%+ 50% sago charcoal bark ash, + T13: 50% Egypt sago rock bark phosphate ash, T11: + 50% Egypt charcoal rock + 25%phosphate sago bark + ash, 25% and charcoal T14: Egypt + 50% rock phosphate + 25% charcoal + 25% sago bark ash. Means with different letter(s) within the same incubation period indicate sago bark ash, T12: Egypt rock phosphate + 75% charcoal + 25% sago bark ash, T13: Egypt rock significant differences between treatments according to Tukey’s HSD test at p ≤ 0.05, i.e., a > b > c. Bars represent the mean phosphate + 50% charcoal + 25% sago bark ash, and T14: Egypt rock phosphate + 25% charcoal + values ± SE. 25% sago bark ash. Means with different letter(s) within the same incubation period indicate significant differences betweenThe treatments percentages according of inorganic to Tukey’s P following HSD the test application at p ≤ 0.05, of i.e., ERP, acharcoal, > b > c. Bars andsago represent the mean valuesbark ash ± SE. are summarised in Figures 22 and 23. The proportions of Sol-P and Red-P were limited compared with other fractions, despite the addition of ERP to the soil. Previous −1 3.4. Percentages of Soilfindings Inorganic (Figure Phosphorus 16) showed thatDist Sol-Pribution ranged by fromTreatment 0.05 to af 1.67ter mg Thirty, kg . Sixty, The distribution and of Red-P was only significant in the soil alone (T1), whereas for the other treatments, the Ninety Days of Incubationamount was negligible because throughout the incubation study, the maximum amount of The initial inorganicRed-P was P 0.97speciation mg kg−1 of(Figure the soil19). Irrespectiveused in this of incubationpresent study time, T1 was had in Fe-P the which order of Fe-P (67%)was > Occl-P more than (12%) half of > theAl-P soil (11%) inorganic > Ca-P P fractions (7%) (ranging > Red-P from (3%) 64% > to Sol-P 80%). (Table As ERP was applied to the soil, Ca-P became dominant (>74%), replacing Fe-P. Additionally, treatments 2). Although the orderwith differed ERP, charcoal, from and that sago reco barkrded ash in demonstrated a study carried a significant out by reduction Hasbullah in Al-P et and al. [78]—Fe-P (68%)Fe-P, > Al-P from (13%) 88% to approximately> Red-P (10%) 13% > atOccl-P 30 DAI, (7%) 86% to> approximatelyCa-P (2%) > Sol-P—both 14% at 60 DAI, and findings are consistent81% towith approximately that reported 15% by at 90 Bidin DAI. [79], The fixation who mentioned of P in Occl-P that of T1Fe-P was is observed dom- to inant in Malaysian increasesoils, with from an 4% average in 30 DAI of to 79%. 7% in 60 DAI, and 10% in 90 DAI, whereas for the other The percentagestreatments, of inorganic the distribution P following of Occl-P the was application within the rangeof ERP, of 3% charcoal, to 6%, irrespective and sago of the incubation time and the rates of charcoal and sago bark ash used. bark ash are summarised in Figures 22 and 23. The proportions of Sol-P and Red-P were limited compared with other fractions, despite the addition of ERP to the soil. Previous findings (Figure 16) showed that Sol-P ranged from 0.05 to 1.67 mg kg−1. The distribution of Red-P was only significant in the soil alone (T1), whereas for the other treatments, the

AgronomyAgronomy 20212021, 11, ,x11 , 1803 21 of21 28 of 28

FigureFigure 22. 22.Percentages Percentages of of soil soil inorganic inorganic phosphorus phosphorus distribution distribution in T1,in T1, T2, T2, T3, T4,T3, T5,T4, T6,T5, andT6, and T7 after T7 after thirty, thirty, sixty, sixty, and ninety and ninety days ofdays incubation, of incubation, where where T1: soil T1: alone, soil T2:alone, Egypt T2:rock Egypt phosphate rock alone, phosphate alone, T3: Egypt rock phosphate + 100% charcoal, T4: Egypt rock phosphate + 100% sago bark ash, T5: Egypt rock phosphate + 100% charcoal + 100% sago bark ash, T6: Egypt T3: Egypt rock phosphate + 100% charcoal, T4: Egypt rock phosphate + 100% sago bark ash, T5: Egypt rock phosphate + 100% charcoal + 100% sago bark ash, T6: Egypt rock phosphate + 75% rock phosphate + 75% charcoal + 75% sago bark ash, and T7: Egypt rock phosphate + 50% charcoal + 75% sago bark ash. charcoal + 75% sago bark ash, and T7: Egypt rock phosphate + 50% charcoal + 75% sago bark ash.

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FigureFigure 23. 23.Percentages Percentages of of soil soil inorganic inorganic phosphorus phosphorus distributiondistribution inin T8,T8, T9, T10, T11, T12, T13, T13, and and T14 T14 after after thirty, thirty, sixty, sixty, and and ninety ninety da daysys of of incubation, incubation, where where T8: T8: Egypt Egypt rock rock phosphate phosphate + 25% + 25% charcoal + 75% sago bark ash, T9: Egypt rock phosphate + 75% charcoal + 50% sago bark ash, T10: Egypt rock phosphate + 50% charcoal + 50% sago bark ash, T11: Egypt rock charcoal + 75% sago bark ash, T9: Egypt rock phosphate + 75% charcoal + 50% sago bark ash, T10: Egypt rock phosphate + 50% charcoal + 50% sago bark ash, T11: Egypt rock phosphate + 25% phosphate + 25% charcoal + 50% sago bark ash, T12: Egypt rock phosphate + 75% charcoal + 25% sago bark ash, T13: Egypt rock phosphate + 50% charcoal + 25% sago bark ash, and T14: charcoal + 50% sago bark ash, T12: Egypt rock phosphate + 75% charcoal + 25% sago bark ash, T13: Egypt rock phosphate + 50% charcoal + 25% sago bark ash, and T14: Egypt rock phosphate + 25% Egypt rock phosphate + 25% charcoal + 25% sago bark ash. charcoal + 25% sago bark ash.

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4. Discussion 4.1. Selected Soil Chemical Properties at Thirty, Sixty, and Ninety Days of Incubation The sago bark ash alone treatment (T4) had a lower effect on TC because C in the sago bark volatilised during combustion to produce ash [55]. Carbon is mostly present in ash in negligible quantities or is even absent. The increase in TC of the soil with charcoal could be attributed to the relatively high C content in the charcoal. According Phounglamcheik et al. [80], the C content in charcoal ranges between 84.0 and 92.1%, but it has a low O, H, and N content. Phonphuak and Thiansem [81] also described charcoal as an amorphous C in the form of highly porous microcrystalline graphite. The increase in the soil pH following the incorporation of charcoal and sago bark ash was due to the basic nature of these amendments (Table3). However, the charcoal alone treatment had lower soil pH compared with the treatments with sago bark ash because sago bark ash has a substantial number of neutralising compounds and base cations. Etiegni and Campbell [53] indicated that hydroxides of Ca, Mg, and K are the main contributors to the soluble alkalinity in wood ash. Their reaction with H+ in the soil solution can form CO2 + H2O and this leads to an increase in pH. The slight increase in the soil pH for T2 suggests that dissolution of Ca and Mg from the applied ERP might have contributed to the increase in soil pH. The reductions in soil exchangeable acidity, Al3+, and Fe2+ for the treatments with charcoal and sago bark ash are related to the increase in soil pH. This ﬁnding is consistent with the ﬁndings of previous studies which also reported that decrease in exchangeable Al3+ and Fe2+ was directly related with the improvement in soil pH [78,82,83]. This was possible because the hydroxyl ions formed from the dissolution of the CaO, MgO, K2O, and NaOH in the ash neutralise the protons in the soil solution and those bound on the cation exchange sites in the soil [84]. The release of the base cations displaced the protons, Al3+, and Fe2+ occupying the cation exchange site. In addition, the reduction can be associated with the adsorption of Al and Fe by the charcoal complexion sites. This also suggests that charcoal is able to reduce Al and Fe solubility by replenishing the functional groups (for example, carboxylic and phenolic) of humic substances. The increase in soil exchangeable H+ of T1 at 30, 60, and 90 DAI was due to further hydrolysis of Al3+ resulting in an increase in the amount of H+. The releasing of H+ was not consistent in this study because there were no plants to contribute to H+ removal through uptake of nutrients. The increase in the exchangeable base cations in the soil with the charcoal and sago bark ash is related to the inherent K, Ca, Mg, and Na contents of these amendments. Ammonium acetate extraction for the wood ash by Ohno and Erich [85] revealed 48% of total Mg, 40% of total K, and 5.7% of total P at pH 3.0, whereas Meiwes [86] reported 81% of total Ca, 57% of total Mg, 34% of total K, and 20% of total P at pH 4.2. Glaser et al. [50] stated that application of charcoal which has ash adds free bases such as K, Ca, and Mg to the soil indirectly provide readily accessible nutrients for plant growth. Moreover, the addition of these base cations to the soil contributes to soil acidity regulation and binding of exchangeable Al and Fe in the soil [87,88]. Although there was an improvement in the soil exchangeable cations, the inconsistency in the soil CEC could be associated with the chemical stability of the charcoal and sago bark ash.

4.2. Total Phosphorus and Mehlich-Phosphorus at Thirty, Sixty, and Ninety Days of Incubation The increase in soil P availability irrespective of treatment could be attributed to mineralisation of organic P in soil [89]. Treatment one had the lowest soil total P and Mehlich-P because there was no addition of mineral P and most of the P ions in the soil were ﬁxed by Al and Fe ions. The lower soil total P value of the treatment with charcoal alone at 60 and 90 DAI indicates that without the sago bark ash, the use of charcoal alone increased soil total P over a short period and the effect lasted for 30 days. The trend of the soil Mehlich-P was different from the soil total P because not all of the soil total P was converted into available form. Some of it was held by the soil particles and organic matter by means of weak outer-sphere mechanisms via anion exchange [90]. The increase in soil Agronomy 2021, 11, 1803 24 of 28

Mehlich-P at 30 DAI might be because of the readily available P released by ERP. At 60 DAI, the soil Mehlich-P decreased because some of the added P was fixed by Al and Fe ions. Recovery of the soil Mehlich-P at 90 DAI suggests that fixed P ions were released into soil solution either through dissolution or desorption reactions as a result of the increase in soil pH. This observation corroborates the findings of Demeyer et al. [55] who demonstrated that P contents in soils are not significantly increased following amendment with wood ash. Comparative studies of P uptake by corn have shown that ash is substantially less effective than P fertilisers [91]. These results confirm the conclusions obtained from the chemical characterisation information on wood ash, because wood ash P is weakly soluble and a large portion of the dissolved P is likely to be immobilised in the soil [92].

4.3. Soil Inorganic Phosphorus Fractions at Thirty, Sixty, and Ninety Days of Incubation The P recovery of the P fractions depends on the P added to the soil, suggesting that an external source of inorganic P is necessary to increase their pool size. The increase in Sol-P for the treatments with charcoal and sago bark ash compared with soil alone and ERP alone is partly related to the readily soluble P released by the charcoal and sago bark ash through mineralisation and dissolution, respectively. However, at 90 DAI, the Sol-P fraction was slightly lower than at 60 DAI because some of the soil solution P might be converted into labile P form as a response to maintain equilibrium of P pools in the soil. The decrease in Al-P and Fe-P following the application of charcoal could be attributed to the production of organic acids during the decomposition of organic material, which temporarily bind to the oxides or hydroxides on the surfaces of clay particles. In addition, sago bark ash as a liming material increases soil pH to reduce the solubility of Al and Fe ions. These chemical reactions prevent P ions from being precipitated with Al and Fe ions. The increase in the Ca-P fraction for the treatments with ERP could be associated with the relatively high concentrations of Ca in this rock phosphate because rock phosphates are generally made up of calcium apatite, which considerably increase Ca-P fraction in soils [93]. The distribution of Red-P was not consistent throughout the incubation study, and this is related to redox reactions involved during the extraction process. The contribution of Occl-P to plant-available P is limited because it is inert to reactions with the soil solution.

4.4. Percentages of Soil Inorganic Phosphorus Distribution after Incubation In acidic soils, P sorption is generally attributed to hydrous oxides of Fe and Al and to (1:1) clays. The dominance of Fe-P fraction of soil alone (T1) is related to lower pH, higher content of Fe, and the weathering processes of soils. These results corroborated findings on acidic soils where Fe-P contributed the largest proportion of inorganic P [94]. However, following the application of ERP, Ca-P in soils increased significantly because of the relatively high Ca in ERP. This result agrees with the studies of Hongqing et al. [93] and Hasbullah [95], who compared inorganic P speciation of soils with TSP and rock phosphate. The findings demonstrate that dissolution of water soluble fertiliser (TSP) in acidic soils produced Al-P and Fe-P, whereas the application of rock phosphate resulted in Ca-P. This occurs because of incomplete dissolution of rock phosphates. Additionally, the higher content of Ca-P in soils with ERP suggests that rock phosphate dissolved slowly to ensure that it supplies P steadily to plants compared with TSP, which dissolves rapidly. The increase in soil pH explains the low recovery of the Al-P and Fe-P fractions for the soil with ERP, charcoal, and sago bark ash. Moreover, the reduction in these fractions is believed to be associated with the precipitation of exchangeable and soluble Al and Fe as well as insoluble Al and Fe hydroxides on the negatively charged functional groups on charcoal’s surfaces. The increase in Occl-P for soil alone suggests that without the incorporation of soil amendments, the occlusion of adsorbed P becomes severe because more adsorbed P is physically encapsulated by secondary minerals such as Al and Fe oxyhydroxides, which are essentially inaccessible to plants because they are inert. Agronomy 2021, 11, 1803 25 of 28

5. Conclusions Co-application of charcoal and sago bark ash with ERP affects inorganic P speciation in soils. Calcium-bound P is more pronounced compared with Al-P and Fe-P in soils with ERP, charcoal, and sago bark ash because these soil amendments are able to increase soil pH, and at the same time, they reduce exchangeable acidity, exchangeable Al, and exchangeable Fe. Additionally, amending acidic soils with charcoal and sago bark ash improves the availability of base cations. Although soil Mehlich-P was not significantly improved with charcoal and sago bark ash, the fact that these soil amendments were able to reduce soil acidity indicates that P fixation by Al and Fe could be solved with the continued use of the amendments to build soil organic matter, which are reputed for improving soil available P with time. Therefore, the findings of this study suggest that the optimum rates of charcoal and sago bark ash to minimise P fixation by Al and Fe are 75% sago bark ash with 75%, 50%, and 25% charcoal. The use of sago bark ash at the rate of 100% is not recommended because it might increase soil salinity and sodicity. Incorporation of sago bark ash with charcoal is essential because charcoal has a high affinity for Al and Fe and its negatively charged surfaces can chelate Al and Fe to free the phosphate ions.

Author Contributions: Conceptualization, P.D.J.; data curation, A.M., L.O. and N.A.H.; formal analysis, P.D.J.; funding acquisition, O.H.A.; investigation, P.D.J.; methodology, O.H.A., A.M., L.O. and N.A.H.; project administration, O.H.A.; supervision, O.H.A., L.O. and N.A.H.; visualization, P.D.J.; writing—original draft, P.D.J.; writing—review and editing, O.H.A., A.M., L.O. and N.A.H. All authors have read and agreed to the published version of the manuscript. Funding: This research was funded by Ministry of Higher Education, Malaysia with grant number [ERGS/1/11/STWN/UPM/02/65]. Institutional Review Board Statement: Not applicable. Informed Consent Statement: Not applicable. Data Availability Statement: The data presented in this study are available within the article. Acknowledgments: The authors would like to acknowledge Ministry of Higher Education, Malaysia for financial assistance and Universiti Putra Malaysia for providing research facilities. Conflicts of Interest: The authors declare no conflict of interest.

References 1. Gichangi, E.M.; Mnkeni, P.N.S.; Muchaonyerwa, P. Phosphate sorption characteristics and external P requirements of selected South African soils. J. Agric. Rural Dev. Trop. Subtrop. 2008, 109, 139–149. 2. Brady, N.C.; Weil, R.R. The Nature and Properties of Soils, 14th ed.; Pearson Prentice Hall: Upper Saddle River, NJ, USA, 2008; pp. 1–31. 3. Meyer, J.B.; Frapolli, M.; Keel, C.; Maurhofer, M. Pyrroloquinoline quinone biosynthesis gene pqqC, a novel molecular marker for studying the phylogeny and diversity of phosphate-solubilizing pseudomonads. Appl. Environ. Microbiol. 2011, 77, 7345–7354. [CrossRef][PubMed] 4. Adnan, A.; Mavinic, D.S.; Koch, F.A. Pilot-scale study of phosphorus recovery through struvite crystallisation-examining to process feasibility. J. Environ. Eng. Sci. 2003, 2, 315–324. [CrossRef] 5. Ch’ng, H.Y.; Ahmed, O.H.; Majid, N.M.A. Improving phosphorus availability in an acid soil using organic amendments produced from agroindustrial wastes. Sci. World J. 2014, 2014, 1–6. [CrossRef] 6. Tsado, P.A.; Osunde, O.A.; Igwe, C.A.; Adeboye, M.K.A.; Lawal, B.A. Phosphorus sorption characteristics of some selected soil of the Nigerian Guinea Savanna. Int. J. Agric. Sci. 2012, 2, 613–618. 7. Li, J.; Shi, Y.L.; Chen, Z.W. Research on phosphorus in southern red soils of China. Chin. J. Soil Sci. 2011, 42, 763–768. 8. Chien, S.H.; Prochnow, L.I.; Tu, S.; Snyder, C.S. Agronomic and environmental aspects of phosphate fertilizers varying in source and solubility: An update review. Nutr. Cycl. Agroecosystems 2011, 89, 229–255. [CrossRef] 9. Wang, Y.L.; Zhang, Y.H.; He, Y.Q. Effect of soil matrix components on phosphate sorption index in red soil. Acta Pedol. Sin. 2012, 49, 552–559. 10. Troeh, F.R.; Thompson, L.M. Soils and Soil Fertility, 6th ed.; Blackwell: New York, NY, USA, 2005. 11. Ch’ng, H.Y.; Ahmed, O.H.; Majid, N.M.A. Improving phosphorus availability, nutrient uptake and dry matter production of Zea mays L. on a tropical acid soil using poultry manure biochar and pineapple leaves compost. Exp. Agric. 2015, 52, 447–465. [CrossRef] Agronomy 2021, 11, 1803 26 of 28

12. Brady, N.C.; Weil, R.R. The Nature and Properties of Soils, 13th ed.; Pearson Education Inc: Upper Saddle River, NJ, USA, 2002. 13. Hinsinger, P. Bioavailability of soil inorganic P in the rhizosphere as affected by root-induced chemical changes: A review. Plant Soil 2001, 237, 173–195. [CrossRef] 14. Takeda, M.; Nakamoto, T.; Miyazawa, K.; Murayama, T.; Okada, H. Phosphorus availability and soil biological activity in an Andosol under compost application and winter cover cropping. Appl. Soil Ecol. 2009, 42, 86–95. [CrossRef] 15. Rahman, Z.A.; Gikonyo, E.; Silek, B.; Goh, K.J.; Soltanghesis, A. Evaluation of phosphate rock sources and rate of application on oil palm yield grown on peat soils of Sarawak, Malaysia. J. Agron. 2014, 13, 12–22. [CrossRef] 16. Elser, J.; Bennett, E. Phosphorus cycle: A broken biogeochemical cycle. Nature 2011, 478, 29–31. [CrossRef][PubMed] 17. Obersteiner, M.; Peñuelas, J.; Ciais, P.; van der Velde, M.; Janssens, I.A. The phosphorus trilemma. Nat. Geosci. 2013, 6, 897–898. [CrossRef] 18. Roy, E.D.; Richards, P.D.; Martinelli, L.A.; Coletta, L.D.; Lins, S.R.M.; Vazquez, F.F.; Willig, E.; Spera, S.A.; VanWey, L.K.; Porder, S. The phosphorus cost of agricultural intensification in the tropics. Nat. Plants 2016, 2, 16043. [CrossRef][PubMed] 19. Zhou, Q.; Zhu, Y. Potential pollution and recommended critical levers of phosphorus in paddy soils of the southern Lake Tai area, China. Geoderma 2003, 115, 45–54. [CrossRef] 20. Ruban, V.; Lopez-Sanchez, J.F.; Pardo, P.; Rauret, G.; Muntau, H.; Quevauviller, P.H. Selection and evaluation of sequential extraction procedures for the determination of phosphorus forms in lake sediments. J. Environ. Monit. 1999, 1, 51–56. [CrossRef] 21. Sharpley, A.; Wang, X. Managing agricultural phosphorus for water quality: Lessons from the USA and China. J. Environ. Sci. 2014, 26, 1770–1782. [CrossRef] 22. Vohla, C.; Kõiv, M.; Bavor, H.J.; Chazarenc, F.; Mander, Ü. Filter materials for phosphorus removal from wastewater in treatment wetlands-A review. Ecol. Eng. 2011, 37, 70–89. [CrossRef] 23. Haynes, R.J.; Mokolobate, M.S. Amelioration of Al toxicity and P deficiency in acid soils by additions of organic residues: A critical review of the phenomenon and the mechanisms involved. Nutr. Cycl. Agroecosystems 2001, 59, 47–63. [CrossRef] 24. Antoniadis, V.; Hatzis, F.; Bachtsevanidis, D.; Koutroubas, S.D. Phosphorus availability in low-P and acidic soils as affected by liming and P addition. Commun. Soil Sci. Plant Anal. 2015, 46, 1288–1298. [CrossRef] 25. Parham, J.A.S.P.; Deng, S.; Raun, W.; Johnson, G. Long-term cattle manure application in soil. Biol. Fertil. Soils 2002, 35, 328–337. [CrossRef] 26. Shamshuddin, J.; Daud, N.W. Classification and management of highly weathered soils in Malaysia for production of plantation crops. Princ. Appl. Assess. Soil Sci. 2011, 2011, 75–86. [CrossRef] 27. Shamshuddin, J.; Fauziah, C.I.; Anda, M.; Kapok, J.; Shazana, M.A.R.S. Using ground basalt and/or organic fertilizer to enhance productivity of acid soils in Malaysia for crop production. Malays. J. Soil Sci. 2011, 15, 127–146. 28. Myers, R.J.K.; De Pauw, E. Strategies for management of soil acidity. In Plant-Soil Interaction at Low pH: Principles and Management; Grundon, N.J., Raiment, G.E., Probert, M.E., Eds.; Springer: Dordrecht, The Netherlands, 1995; pp. 729–741. 29. Shafie, S.M.; Othman, Z.; Hami, N. Potential utilisation of wood residue in Kedah: A preliminary study. J. Technol. Oper. Manag. 2017, 12, 60–69. [CrossRef] 30. Hoi, W.K.; Razak, M.A.; Puad, E.; Azmi, M.H. Wood as a Potential Source of Energy. In Proceedings of the Conference of Forestry and Forest Products Research 90, Forest Research Institute Malaysia, Kepong, Selangor, Malaysia, 3 October 1990. 31. Bujang, K. Potentials of bioenergy from the sago industries in Malaysia. In EOLSS-Encyclopedia of Life Support Systems; Doelle, H.W., Rokem, S., Berovic, M., Eds.; EOLSS Publisher: Oxford, UK, 2006; pp. 124–131. 32. Singhal, R.S.; Kennedy, J.F.; Gopalakrishnan, S.M.; Kaczmarek, A.; Knill, C.J.; Akmar, P.F. Industrial production, processing, and utilization of sago palm-derived products. Carbohydr. Polym. 2008, 72, 1–20. [CrossRef] 33. Vikineswary, S.; Shim, Y.L.; Thambirajah, J.J.; Blakebrough, N. Possible microbial utilization of sago processing wastes. Resour. Conserv. Recycl. 1994, 11, 289–296. [CrossRef] 34. Wahi, R.; Abdullah, L.C.; Mobarekeh, M.N.; Ngaini, Z.; Yaw, T.C.S. Utilization of esterified sago bark fibre waste for removal of oil from palm oil mill effluent. J. Environ. Chem. Eng. 2017, 5, 170–177. [CrossRef] 35. Amin, N.; Sabli, N.M.; Izhar, S.; Yoshida, H. Sago Wastes and Its Applications. Pertanika J. Sci. Technol. 2019, 27, 1841–1862. 36. Ch’ng, H.Y. Phosphorus Management for Tropical Acid Soils Using Amendments from Agro-Industrial Wastes. Ph.D. Thesis, Universiti Putra Malaysia, Serdang, Selangor, Malaysia, 2015. 37. Ohno, T.; Amirbahman, A. Phosphorus availability in boreal forest soils: A geochemical and nutrient uptake modeling approach. Geoderma 2010, 155, 46–54. [CrossRef] 38. Ohno, T.; Fernandez, I.J.; Hiradate, S.; Sherman, J.F. Effects of soil acidification and forest type on water soluble soil organic matter properties. Geoderma 2007, 140, 176–187. [CrossRef] 39. Chen, Q.; Zhang, X.; Zhang, H.; Christie, P.; Li, X.; Horlacher, D.; Liebig, H.P. Evaluation of current fertilizer practice and soil fertility in vegetable production in the Beijing region. Nutr. Cycl. Agroecosyst. 2004, 69, 51–58. [CrossRef] 40. Imbufe, A.U.; Patti, A.F.; Burrow, D.; Surapaneni, A.; Jackson, W.R.; Milner, A.D. Effects of potassium humate on aggregate stability of two soils from Victoria, Australia. Geoderma 2005, 125, 321–330. [CrossRef] 41. Galinato, S.; Yoder, J.; Granatstein, D. The economic value of biochar in crop production and carbon sequestration. Energy Policy 2011, 39, 6344–6350. [CrossRef] 42. Lehmann, J. A handful of carbon. Nature 2007, 447, 143–144. [CrossRef] Agronomy 2021, 11, 1803 27 of 28

43. DeLuca, T.H.; Aplet, G.H. Charcoal and carbon storage in forest soils of the Rocky Mountain West. Front. Ecol. Environ. 2008, 6, 18–24. [CrossRef] 44. Ogawa, M. Rehabilitation of Pine with Charcoal and Mycorrhiza; Chikushishokan Publishing: Tokyo, Japan, 2007. 45. Herrmann, S.; Oelmuller, R.; Buscot, F. Manipulation of the onset of ectomycorrhiza formation by indole-2-acetic acid, activated charcoal or relative humidity in the association between oak micocuttings and Piloderma croceum: Influence on plant development and photosynthesis. J. Plant Physiol. 2004, 161, 509–517. [CrossRef] 46. Topoliantz, S.; Ponge, J.F.; Ballof, S. Manioc peel and charcoal: A potential organic amendment for sustainable soil fertility in the tropics. Biol. Fertil. Soils 2005, 41, 15–21. [CrossRef] 47. Rutto, K.L.; Mizutani, F. Effect of mycorrhizal inoculation and activated charcoal on growth and nutrition in peach (Prunus perisica Batsch) seedlings treated with peach root-bark extracts. J. Jpn. Soc. Hortic. Sci. 2006, 75, 463–468. [CrossRef] 48. Warnock, D.D.; Lehmann, J.; Kuypern, T.W.; Rilling, M.C. Mycorrhizal response to charcoal in soil-concepts and mechanisms. Plant Soil 2007, 300, 9–20. [CrossRef] 49. Grogan, P.J.; Baar, T.; Bruns, D. Below-ground ectomycorrhizal community structure in a recently burned bishop pine forest. J. Ecol. 2000, 88, 1051–1062. [CrossRef] 50. Glaser, B.; Lehmann, J.; Zesh, W. Ameliorating physical and chemical properties of highly weathered soils in the tropics with charcoal-a review. Biol. Fertil. Soil 2002, 35, 219–230. [CrossRef] 51. Lehmann, J.; da Silva, J.P., Jr.; Rondon, M.; Cravo, M.D.S.; Greenwood, J.; Nehls, T.; Steiner, C.; Glaser, B. Slash-and-char-a feasible alternative for soil fertility management in the central Amazon. In Proceedings of the 17th World Congress of Soil Science, Bangkok, Thailand, 14 August 2002. 52. Tryon, E.H. Effect of charcoal on certain physical, chemical, and biological properties of forest soils. Ecol. Monogr. 1948, 18, 81–115. [CrossRef] 53. Etiegni, L.; Campbell, A.G. Physical and chemical characteristics of wood ash. Bioresour. Technol. 1991, 37, 173–178. [CrossRef] 54. Ohno, T. Neutralization of soil acidity and release of phosphorus and potassium by wood ash. J. Environ. Qual. 1992, 21, 433–438. [CrossRef] 55. Demeyer, A.; Nkana, J.V.; Verloo, M. Characteristics of wood ash influence on soil properties and nutrient uptake: An overview. Bioresour. Technol. 2001, 77, 287–295. [CrossRef] 56. Khanna, P.K.; Raison, R.J.; Falkiner, R.A. Chemical properties of ash derived from Eucalyptus litter and its effects on forest soils. For. Ecol. Manag. 1994, 66, 107–125. [CrossRef] 57. Ludwig, B.; Rumpf, S.; Mindrup, M.; Meiwes, K.J.; Khanna, P.K. Effects of lime and wood ash on soilsolution chemistry, soil chemistry and nutritional status of a pine stand in northern Germany. Scand. J. For. Res. 2002, 17, 225–237. [CrossRef] 58. Saarsalmi, A.; Mälkönen, E.; Piirainen, S. Effects of wood ash fertilization on forest soil chemical properties. Silva. Fenn. 2001, 35, 355–368. [CrossRef] 59. Ferriero, A.; Merino, A.; Diaz, N.; Pineiro, J. Improving the effectiveness of wood-ash fertilization in mixed mountain pastures. Grass Forage Sci. 2011, 66, 337–350. [CrossRef] 60. Dixon, R.K.; Wisniewski, J. Global forest systems: An uncertain response to atmospheric pollutants and global climate change. Water Air Soil Pollut. 1995, 85, 101–110. [CrossRef] 61. Bouyoucos, G.J. Hydrometer method improved for making particle size analysis of soils. Agron. J. 1962, 54, 464–465. [CrossRef] 62. Peech, H.M. Hydrogen-ion Activity. In Methods of Soil Analysis Chemical and Microbiological Properties; Black, C.A., Evans, D.D., White, J.L., Ensminger, L.E., Clark, F.E., Eds.; American Society of Agronomy: Madison, WI, USA, 1965; pp. 914–926. 63. Chefetz, B.; Hatcher, P.H.; Hadar, Y.; Chen, Y. Chemical and biological characterization of organic matter during composting of municipal solid waste. J. Environ. Qual. 1996, 25, 776–785. [CrossRef] 64. Bremner, J.M. Total Nitrogen. In Methods of Soil Analysis: Part 2; Black, C.A., Evans, D.D., Ensminger, L.E., White, J.L., Clark, F.F., Dinauer, R.C., Eds.; American Society of Agronomy: Madison, WI, USA, 1965; pp. 1149–1178. 65. Cottenie, A. Soil testing and plant testing as a basis of fertilizer recommendation. FAO Soils Bull. 1980, 38, 70–73. 66. Rowell, D.L. Soil Science: Methods and Application; Longman Publishers Ltd.: London, UK, 1994; p. 169. 67. Bernas, B. New method for decomposition and comprehensive analysis of silicates by atomic absorption spectrometry. Anal. Chem. 1968, 40, 1682–1686. [CrossRef] 68. Mehlich, A. Determination of P, Ca, Mg, K, Na and NH4. Short Test Methods Used in Soil Testing Division; Department of Agriculture: Raleigh, NC, USA, 1953. 69. Kuo, S. Phosphorus. In Methods of soil analysis. Part 3: Chemical Methods; Sparks, D.L., Ed.; The American Society of Anesthesiolo- gists, Soil Science Society of America: Madison, WI, USA, 1996; pp. 869–920. 70. Murphy, J.; Riley, J.P. A modified single solution method for the determination of phosphate in natural waters. Anal. Chim. Acta 1962, 27, 31–36. [CrossRef] 71. Paramananthan, S. Soil of Malaysia: Their Characteristics and Identification; Academy of Sciences Malaysia: Kuala Lumpur, Malaysia, 2000; Volume 1, pp. 11–125. 72. Malaysian Agricultural Research and Development Institute (MARDI). Jagung Manis Baru, Masmadu [New Sweet Corn, Masmadu]; Malaysian Agricultural Research and Development: Serdang, Selangor, Malaysia, 1993; pp. 3–5. 73. Free, H.F.; McGill, C.R.; Rowarth, J.S.; Hedley, M.J. The effect of biochars on maize (Zea mays) germination. N. Z. J. Agric. Res. 2010, 53, 1–4. [CrossRef] Agronomy 2021, 11, 1803 28 of 28

74. Ndor, E.; Dauda, S.N.; Azagaku, E.D. Response of maize varieties (Zea mays) to biochar amended soil in Lafia, Nigeria. J. Exp. Agric. Int. 2015, 5, 525–531. [CrossRef] 75. Mandre, M.; Pärn, H.; Ots, K. Short-term effects of wood ash on the soil and the lignin concentration and growth of Pinus sylvestris L. For. Ecol. Manag. 2006, 223, 349–357. [CrossRef] 76. Ozolincius, R.; Buozyte, R.; Varnagiryte, K.I. Wood ash and nitrogen influence on ground vegetation cover and chemical composition. Biomass Bioenergy 2007, 31, 710–716. [CrossRef] 77. Perucci, P.; Monaci, E.; Onofri, A.; Vischetti, C.; Casucci, C. Changes in physico-chemical and biochemical parameters of soil following addition of wood ash: A field experiment. Eur. J. Agron. 2008, 28, 155–161. [CrossRef] 78. Hasbullah, N.A.; Ahmed, O.H.; Ab Majid, N.M. Effects of Amending Phosphatic Fertilizers with Clinoptilolite Zeolite on Phosphorus Availability and Its Fractionation in an Acid Soil. Appl. Sci. 2020, 10, 3162. [CrossRef] 79. Bidin, A. Phosphorus utilization in rainfed agriculture in Malaysia. In Proceedings of the Second IMPHOS Regional Seminar: Southern Asia, Fertility Association of India, New Delhi, India, 26–30 August 1986; pp. 161–172. 80. Phounglamcheik, A.; Wang, L.; Romar, H.; Kienzl, N.; Broström, M.; Ramser, K.; Skreiberg, Ø.; Umeki, K. Effects of Pyrolysis conditions and feedstocks on the properties and gasification reactivity of charcoal from woodchips. Energy Fuels 2020, 34, 8353–8365. [CrossRef] 81. Phonphuak, N.; Thiansem, S. Effects of charcoal on physical and mechanical properties of fired test briquettes. Sci. Asia 2011, 37, 120–124. [CrossRef] 82. Asap, A.; Haruna, A.O.; Majid, N.M.A.; Ali, M. Amending triple superphosphate with chicken litter biochar improves phosphorus availability. Eurasian J. Soil Sci. 2018, 7, 121–132. [CrossRef] 83. Ch’ng, H.Y.; Sanusi, S.; Othman, S.B. Effect of Christmas Island rock phosphate and rice straw compost application on soil phosphorus availability and maize (Zea mays L.) growth in a tropical acid soil of Kelantan, Malaysia. Open Agric. 2020, 5, 150–158. [CrossRef] 84. Saarsalmi, A.; Mälkönen, E.; Kukkola, M. Effect of wood ash fertilization on soil chemical properties and stand nutrient status and growth of some coniferous stands in Finland. Scand. J. For. Res. 2004, 19, 217–233. [CrossRef] 85. Ohno, T.; Erich, M.S. Effect of wood ash application on soil pH and soil test nutrient levels. Agric. Ecosyst. Environ. 1990, 32, 223–239. [CrossRef] 86. Meiwes, K.J. Application of lime and wood ash to decrease acidification of forest soils. Water Air Soil Pollut. 1995, 85, 143–152. [CrossRef] 87. Ch’ng, H.Y.; Haruna, A.O.; Majid, N.M.N.A.; Jalloh, M.B. Improving soil phosphorus availability and yield of Zea mays L. using biochar and compost derived from agro-industrial wastes. Ital. J. Agron. 2019, 14, 34–42. [CrossRef] 88. Sanusi, S.; Ch’ng, H.Y.; Othman, S. Effects of incubation period and Christmas Island rock phosphate with different rate of rice straw compost on phosphorus availability in acid soil. AIMS Agric. Food 2018, 3, 384–396. [CrossRef] 89. Noack, S.R.; McLaughlin, M.J.; Smernik, R.J.; McBeath, T.M.; Armstrong, R.D. Phosphorus speciation in mature wheat and canola plants as affected by phosphorus supply. Plant Soil 2014, 378, 125–137. [CrossRef] 90. Penn, C.J.; Camberato, J.J. A critical review on soil chemical processes that control how soil pH affects phosphorus availability to plants. Agriculture 2019, 9, 120. [CrossRef] 91. Erich, M.S.; Ohno, T. Phosphorus availability to corn from wood ash-amended soils. Water Air Soil Pollut. 1992, 64, 475–485. [CrossRef] 92. Erich, M.S. Agronomic effectiveness of wood ash as a source of phosphorus and potassium. Am. Soc. Agron. Crop. Sci. Soc. Am. Soil Sci. Soc. Am. 1991, 20, 576–581. [CrossRef] 93. Hongqing, H.; Chunying, T.; Chongfa, C.; Jizheng, H.; Xueyuan, L. Availability and residual effects of phosphate rocks and inorganic P fractionation in a red soil of Central China. Nutr. Cycl. Agroecosyst. 2001, 59, 251–258. [CrossRef] 94. Hasbullah, N.A.; Osumanu, H.A.; Nik, M. Effects of Clinoptilolite zeolite on phosphorus dynamics and yield of Zea mays L. cultivated on an acid soil. PLoS ONE 2018, 13, e0204401. [CrossRef] 95. Hasbullah, N.A. Use of Clinoptilolite Zeolite to Improve Efficiency of Phosphorus Use in Acid Soils. Ph.D. Thesis, Universiti Putra Malaysia, Serdang, Selangor, Malaysia, 2016.