Forms and Dynamics of Soil Potassium in Acid Soil in the Wolaita Zone of Southern Ethiopia

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Forms and dynamics of soil potassium in acid soil in the wolaita zone of southern Ethiopia

Mesfin Kassa1, Fassil Kebede2, Wassie Haile3 1Department of Plant Science, College of Agricultural, Wolaita Sodo University, P.O,Box 138 3 School of Plant and Horticultural Science, Hawassa University, P. O. Box 05, Hawassa, Ethiopia,2Mohammed VI Polytechnic University Lot 660,Haymoulary Rachid 43150, Banguerir, Morocco *Corresponding Email: [email protected]

ABSTRACT Quantity-intensity (Q/I) characteristics are among conventional approaches for studying potassium dynamics and its availability. This was assessed to determine availability in four districts: namely, Sodo Zuria, Damot Gale, Damot Sore, and Boloso Sore at three different land use type viz., enset-coffee, crop land, and grazing land. Fractionation and dynamics of K studied in soil samples, which were collected from 0-20 cm depth of each land type. The -1 study revealed that water extractable K concentrations ranged from 0.04 to 0.42 CmolCKg -1 soils with a mean of 0.17 CmolCKg at enset-coffee and grazing land use types, -1 1 respectively, and had a mean value of 0.28 CmolCKg soils ammonium acetate extractable -1 1 K and nitric acid extracted K had a mean value of 0.25 CmolCKg soils. The proportion of water K was found to be the lowest. In this study, the mean of non-exchangeable and -1 exchangeable K concentrations were means of 0.14 and 0.11 CmolCKg soils for land use types. Significant correlations were found between soil properties and Q/I parameters; and among equilibrium solution parameters and Q/I parameters. There was no significant variation among the mean quantity values of the soils. The soils had higher change in exchangeable K and potential buffering capacity than the enset- coffee land use soils; and the cop land had the highest values for these parameters. However, the enset- coffee land use soils had higher K-intensity. Therefore, application of site specific soil fertility management practices and research can improve soil K status and Q/I parameters to sustain productivity soils. Key words: Quantity-intensity, soil properties, thermodynamic 1. Introduction Potassium is an essential and major nutrient for agricultural crop production (George and Michael, 2002). Potassium exists in four forms in the soil, such as solution, exchangeable, non-exchangeable or fixed and mineral or structural K forms (Sparks, 2000).The distribution of soil K among water soluble, exchangeable and non-exchangeable forms, is related to many soil properties including surface area, mineralogy, surface charge density and degree of inter layering of clay minerals (Rahmatullah and Mengel, 2000). There are dynamic, equilibrium reactions between different forms of K. Amount in a soil depends on the parent material, degree of weathering, fertilizer, losses due to crop removal, erosion and leaching (Ajiboye et al.,2015). Quantity-intensity relationship has been used to measure the availability of potassium in soils (Otobong et al., 2012). This relationship implies that the ability of a soil system to maintain a certain concentration of a cation in solution is determined by the total amount of the cation present in readily available forms (exchangeable and soluble) and the intensity by which it is released into the soil solution (Ajiboye et al.,2015). Various interpretations of the thermodynamic parameters have been made, which can be derived from a Q/I plot. In some cases even though the soil contain considerable amount of K, the availability to plants are negligible because of the availability of K to plants depends not only on its availability but also on its dynamics viz., intensity, capacity, and renewal rate in soils, the equilibrium constants is vital for predicting the status and supply of K for plant (Abaslou

and Abtahi, 2008). Inadequate and unbalanced fertilizer application may be one reason for declining K nutrition in crop fields that results in lower crop yield. The low levels of exchangeable K in many of the farming was contradicts with the generally held view that Ethiopia soils are rich in potassium. Several studies revealed that any activity associated with change in land use and agricultural management practices can affect soil properties and K dynamics (Ghiri et al.,2011; Hannan,2008; Haile and Mamo,2013; Ajiboye et al.,2015), but the exchangeable and extractable K status of Wolaita soil K forms are unsatisfactory measures of nutrient availability since their concentration in the soil at any time is small in relation to long term losses by crop removal and leaching and give little indication of reserves of non-exchangeable but potentially available K. Recent soil tests showed that the available K concentrations of soils forms were below 0.5 cmolkg-1 soil, indicating they are becoming K- deficient. As limited research results are available on the balance of K for crop land systems in Wolaita, The ability to predict yield responses to K fertilizers from K soil tests is limited and requires study, the objectives of this study were to: 1) determine physical and chemical properties of the soils, 2) assess different types of K forms and dynamic in the different land uses 2. Materials and methods 2.1. Description of the study sites The study sites were located in Sodo Zuria, Damot Gale, Damot Sore and Boloso Sore districts of the wolaita zone of southern Ethiopia (Fig.1) during 2015. Wolaita zone is situated between Longitude 37°35ʹ30” to 38°58ʹ36”N and Latitude 6°57ʹ20”to 7°04ʹ31”E, with altitude ranges from 1895 to 2260 masl. The average annual rainfall ranges from 1000 to 1394.82 mm with mean annual temperature of 19.93°C (NMA, 2016). The main crops grown in the area include: maize, beans, bananas, sugarcane, coffee, cassava, and cabbage. The dominant soil around Wolaita area is Eutric Nitisols, associated with Humic Nitisols and mineralogy of the soil is kaolinite (Tesfaye, 2003; Mesfin et al., 2015).

Fig.1. Locations map of the Wolaita zone in Ethiopia

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200 Rain Fall Temp Max Temp Min 30 180 160 25

140 20 120 100 15

80 Temp(0C)

RainFall RainFall (mm) 60 10 40 5 20 0 0 Jan Feb Mar Apr MayMonthJun Jul Aug Sep Oct Nov Dec Fig.2. Nine years (2008- 2016) mean monthly rainfall and mean maximum and minimum temperatures of the study areas (NMA, 2016) 2.2. Site selection, soil sampling procedures, and layout The sites and land use types were selected by conducting visual physical observation of the area was carried out to have a general view of the variations in the study during 2014.During physical observation, the geographical position of the area was observed, which are similar in their agroecology, altitude and slope were selected purposively. After the selection of the two peasant association, the land use types were systematically selected on the basis of geographical position, similarity in soil color by visual observation, slope and altitude to reduce their natural difference as well as soil type diversity impacts on the soil acidity. Different land use types (enset- coffee, crop and grazing lands) that are adjacent to each other were selected for soil sampling sites. Sampling from each land use types and locations were replicated four times. Therefore, a total of 48 disturbed soil samples were collected, then the collected soil samples were composited treatment wise to12 representative composite soil samples. Finally, the composite soil samples were subjected to laboratory analysis for selected soil physical and chemical properties. 2.3. Soil laboratory analyses All Laboratory analyses were done by following the procedures in laboratory manual prepared by Sahlemedhin and Taye (2000).Particle size distribution was determined by hydrometer method (Day, 1965). Soil pH and electrical conductivity (ECe) were measured using 1:2.5 soil: water ratio (Page, 1982), whereas organic carbon (OC) by wet digestion method (Walkley and Black, 1954). Total N was determined by Kjeldahl wet digestion and distillation method (Jackson, 1973), available P by using Bray II method (Bray and Kurtz, 1945), and available potassium by Morgan (1941).The cation exchange capacity (CEC) and exchangeable bases were extracted by 1 M ammonium acetate (pH 7) method (Chapman, 1965). In the extract, exchangeable Ca and Mg were determined by atomic absorption spectrophotometer (AAS) and exchangeable K and Na by flame photometer. Calcium carbonate was determined by the acid neutralization method and exchangeable acidity was determined by titration with NaOH after extraction with 1N KCl in the ratio 1:20 and exchangeable acidity was determined. Available micronutrients (Fe, Mn, Zn and Cu) of the soil were extracted by diethylenetriaminepentaacitic acid method (Tan, 1996) and determined using AAS. The water soluble (H2O-K), ammonium acetate extractable potassium (NH4OAC-K) and nitric acid extract potassium (HNO3- K) were determined by the methods described by Pratt (1965). Exchangeable K(Exch-K) was calculated by subtracting H2O- K from NH4OAC-K and non exchangeable K was calculated subtracting (Exch-K) from INHNO3 extractable K were obtained according to the mathematical procedures used by

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(Samadi et al., 2008).The concentration of potassium in all extracts was measured by flame photometer. Quantity-Intensity (Q/I) isotherm was constructed according to the modified by Wang et al. (2004). To a series of 100 ml shaking bottles duplicate with soil samples of five gm, each shaking bottle with soil, 30 ml of 0.01M CaCl2 solutions was added. The concentrations of KCl used were 0, 0.2, 0.4, 0.8, 2.0, 4.0, and 8.0molKL-1. The bottles with contents were shaking for 1hr, kept overnight and centrifuged at 2000 rpm from 10 min. The supernatant solutions were collected and analyzed for K, Ca, and Mg and the K were determine by flame photometer while Ca, Mg were determined by AAS. An activity ratio was 2 ½ calculated with the Debye-Huckel equation, logγi = – 0.509 Z I . Where: Z: valence of ion, γi = activity coefficient, I = Ionic strength. All equations that calculate activity coefficients were based on a solution parameter termed of ionic strength. Ionic strength (I) (μ) molL-1 in soil extracts were calculated by the formula proposed by Griffin and Jurinak (1993): I = 0.0129 ECe (dSm-1). Activities of potassium, calcium and magnesium in the extracts were calculated as product of concentration of ions multiplied by their activity coefficient (γ) values. Activity (α) = γM. Where M = concentration of the cations in solution (molsL-1). The activities (a) ratio of K in the solutions were determined by using the equation ARK ( ) the free energy of replacement (-ΔF) of K was calculated by the formula proposed by Woodruff (1955): -ΔF = 2.303RTLogARK.Where R is gas constant (1.987 Cal.K mol-1) and T is the absolute temperature 25°C, lower than (ΔF) - 3500 cal.mol-1 , -3500 to -2000 cal.mol-1 , and greater than -2000 cal mol-1 soil have poor, medium, and high supplying power of potassium, respectively. The gain/loss of K (±ΔK) in relation to the adsorbed phase was calculated by measuring the corresponding increase or decrease in the concentration of K in the equilibrium solution, compared to the original solution. Potassium buffering capacity (PBCK) = ±ΔK0/AReK. Where, -ΔK0 = Labile K (Quantity of K released), AReK = Equilibrium activity ratio. The quantity factor represents the change in exchangeable potassium (±ΔK) = [K] original - [K] equilibrium or the change in the amount of exchangeable potassium (±ΔK) which represents the quantity factor was calculated from the differences of concentrations of potassium in prepared solutions and equilibrated solution and the intensity factor is the activity ratio of potassium. 2.4. Statistical analysis Data was subjected to analysis of variance (ANOVA) by using SAS software. Treatment means were compared using LSD at Probability 5 % level. 3. Results and discussion 3.1. Selected physical and chemical properties of the soils The textural class determinations revealed that the soils were dominated by sandy clay loam, whereas silt loam (crop land) and sandy loam (grazing) the fractions (Table 1). Accordingly, the soil texture varied from silt loam to loam in the crop land. This might be attributed to the removal of fine soil particles from crop land and their deposition at lower surface. The soil pH KCl & H2O varied from 4.08 to 5.60, 5.05 to 6.61 in enset coffee and crop land, respectively, which are slightly acidic and very acidic (Hazelton and Murphy, 2007). In addition, higher pH (6.6) was recorded under enset coffee as compared crop land (5.05), which could be attributed to the relatively high erosion and leaching of exchangeable bases. Ishibashi et al. (2004) reported that the increasing rates of nitrogenous fertilizers also increase soil acidity. The OC of the soils ranged from 0.49 to 2.02 % under different land use, higher OC (2.02 %) was recorded under enset coffee as compared crop land (0.49 %), which could be attributed to increase the biological soil macro organism, soil moisture and aeration, dominance of roots, humus, and addition of biomass under enset coffee land system. Similarly, Yihenew (2002) stated that Ethiopia cultivated soils of are poor in organic matter due to low amount of organic materials applied to the soil and nearly complete removal of the biomass from the field. Accordance to Landon (1991) classification TN was low in all

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experimental sites. Total N was significantly (P ≤ 0.05) affected by land use and location interactions (Table 1). Comparatively, the highest (0.18 %) was recorded under enset coffee and lowest (0.11 %) under crop land. Available P content of the soils ranged from 6.4 to 18.96 mg kg-1 and was low in accordance with rating Landon (1991) throughout the locations (Table 1) indicating its inadequacy for crop production could be attributed to -1 fixation on both clay surface. The CEC of the soils ranged from 15 to 24 CmolCkg soils and was medium value as per the rating of Hazelton and Murphy (2007). The soil was low in exchangeable base which is due to the higher rainfall and seasonal variation normally observed in the area leading to intense leaching of bases and accumulation of exchangeable acidity in these soils. Highly significant (P ≤ 0.01) differences were observed in available micronutrients of Fe, Mn and Zn contents by the interaction effect of land uses and locations where as the highest (178.2, 144 and 16.20 mg kg-1) were observed under the crop and grazing land (Table 1), which might be due to OM concentrations that acted as a chelating effect and source of such micronutrients. Significant difference was observed in Cu content where the highest (4.98 mg kg-1) was recorded under grazing land that might be also due to its soil OM contents. The Cu deficiency in the study areas could be linked with low soil OM, intensive cropping systems and over grazing and non-use of Cu containing fertilizer could result in high Cu mining. This result is in agreement with that of Alemayehu and Sheleme (2013) who reported that available Cu was deficiency in enset and maize land use types.

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Table.1. Selected physical and chemical properties of the soils as influenced by land uses and locations. SCL=sand clay loam, L= loam, SL=sandy loam, CL=clay loam, SiL=silt loam, SCL=sandy clay loam, L= loam, SiL = silt loam, Sodo Zuria Damot Gale Damot Sore Boloso Sore (n=48) Land use Land use Land use Land use Soil properties EncL CL GL EncL CL GL EncL CL GL EncL CL GL Means CV LSD (%) (5%) Sand (%) 54.00 38.01 68.00 36.00 26.00 60.00 36.00 19.0 27.00 40.00 28.00 30.00 37.49 2.95 0.93 Silt (%) 22.00 44.01 20.00 37.00 50.00 16.00 42.00 55.0 51.00 36.00 50.00 40.00 36.86 6.13 1.90 Clay (%) 24.00 18.00 12.00 27.00 24.00 24.00 26.00 22.0 22.00 24.00 22.00 30.00 20.91 9.56 1.68 Textural class SCL L SL CL SiL SCL L SiL SiL L SiL CL - - - pH ( H2O) 6.36 5.56 5.97 6.61 5.05 5.52 6.12 5.54 6.01 5.92 5.05 5.08 5.88 11.87 0.58 pH ( KCl) 5.38 4.40 4.86 5.60 4.84 4.08 5.07 4.23 4.23 5.09 5.55 4.76 4.85 4.85 0.19 OC (%) 1.95 1.56 1.61 2.12 1.56 2.02 2.34 0.49 0.98 2.44 0.88 1.12 1.81 7.75 0.11 ECe(dSm-1) 0.15 0.53 0.42 0.11 0.32 0.43 0.21 0.33 0.23 0.55 0.43 0.52 0.35 4.80 0.17 Available P (mg kg-1) 17.50 7.50 10.30 19.10 6.90 6.40 17.09 7.20 7.19 18.96 7.39 6.97 10.67 5.53 0.49 Available K (mg kg-1) 306.8 149.3 180.7 314.8 123.9 197.8 264.5 105 141.8 234.6 158.3 223.6 195.12 2.52 2.11 TN % 0.18 0.15 0.15 0.18 0.11 0.11 0.16 0.12 0.12 0.14 0.14 0.13 0.14 3.61 0.04 Exch. K (cmolkg-1) 0.17 0.16 0.15 0.18 0.07 0.05 0.19 0.05 0.13 0.11 0.04 0.05 0.11 9.28 0.01 Exch.Ca (cmolkg-1) 12.40 10.60 11.40 11.60 10.60 11.60 14.40 12.6 14.50 14.60 12.40 13.20 12.15 4.74 0.48 Exch. Mg (cmolkg-1) 7.44 5.74 7.58 6.74 5.15 6.26 7.44 6.15 7.26 6.64 5.25 6.96 6.16 7.14 0.37 Exch.Na (cmolkg-1) 0.27 0.13 0.14 0.29 0.37 0.41 0.36 0.35 0.35 0.39 0.39 0.34 0.28 10.14 NS CEC (cmolkg-1) 22.00 15.00 17.00 20.00 15.00 17.00 23.00 20.0 24.00 23.00 20.00 21.00 19.08 6.05 0.97 CaCO3 (%) 21.50 19.70 21.20 22.20 18.50 19.70 23.00 19.6 20.20 22.90 20.00 21.60 20.50 2.81 0.48 DTPA Fe (mg kg-1) 74.00 102 96.00 124.00 146.00 134.0 121.0 164 157.0 165.0 178.0 168 134.38 1.75 1.90 DTPA Mn (mg kg-1) 98.00 115.0 105.0 128.00 145.00 138.0 108.0 157 144.0 105.0 135.0 125.0 223.58 2.35 2.43 DTPA Zn (mg kg-1) 8.20 10.20 8.80 10.60 11.80 11.20 12.20 14.2 12.40 15.8 16.20 15.80 12.00 4.80 0.48 DTPA Cu (mg kg-1) 3.40 1.80 3.20 3.20 1.50 4.80 4.80 1.60 4.74 4.83 1.92 4.98 3.06 8.84 0.48 Exchangeable acidity 0.42 0.64 0.56 0.37 0.51 0.47 0.32 0.40 0.40 0.32 0.56 0.44 0.41 13.82 NS (cmolkg-1) CL= clay loam, EncL=Enset coffee system, CL= Crop land, GL=Grazing land

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3.2. Effects of land use types on soil potassium forms

-1 The H2O-K in the soils ranged from 0.04 to 0.42 Cmolckg soil under different land uses and was high according to IPI (2001). Significantly higher H2O-K was observed under enset -1 coffee complex compared to grazing land (0.04 Cmolckg soil), showed that solution K constitutes an insignificant fraction of K available for plant uptake or leaching in the various -1 -1 land use types. Other workers have reported 0.002 Cmolckg soil to 0.02 Cmolckg soil for -1 major Lebanese agricultural soils (Al-Zubaidi et al., 2008) and 0.004 Cmolckg soil to 0.046 -1 Cmolckg soil for paddy and non-paddy rice soils in Iran (Raheb and Heidari, 2011). The -1 NH4OAc-K in the soils ranged from 0.17 to 0.61 Cmolckg soil and was low in accordance with the rating (Darwish et al. (2003). Highly significant (p ≤ 0.001) difference was observed in NH4OAc- K by the interaction effects of land uses and locations where as the highest was observed in the enset coffee land as compared to crop and grazing lands, which might be long-term over grazing and continuous cropping without replenishing with potassium fertilizers (Table 3.2). This result is in agreement with that of Darwish et al. (2003) who - reported that NH4OAC- K values for some Lebanese soils, ranged from 0.4 to 2.0 Cmolckg 1 -1 soil , 132.74 to 546.59 mg kg for soils under banana land use in Ethiopia (Ayele, 2013) and 49.70 to 803.14 for rice in tropical savanna climate of Thailand soils (Ngwe et al., 2012). The -1 HNO3 - K in the soils ranged from 0.14 to 0.40 Cmolckg soil and was low in accordance with -1 the rating of FAO-UNESCO (1997). Significantly highest (0.40 Cmolckg soil) was observed under enset coffee as compared to crop and grazing lands (Table 2), which is attributed to the different types parent rock and mineralogy of the studied soils and the soil supplying power for potassium for long term cropping and the soils have poor supplying power of potassium for future cropping and plant growth. This result is in agreement with that of Al-Zubaidi (2003) who reported on Iraqi soils (580 to 2200 mg kg-1). The data presented in Table 2 -1 indicated that value of exchangeable K ranged from 0.05 to 0.0.19 Cmolckg soil. It was highly significantly (P ≤ 0.001) affected by land uses and locations interactions whereby the -1 highest (0.19 Cmolckg soil) was observed under enset coffee as compared to crop land, that show the exchangeable K status of these soils were low for sustainable crop production in crop land uses, thus the need for supplemental application of K fertilizer and crop land soils have exchangeable K occupancy of the exchange sites. Al-Zubaidi et al. (2008) suggested that the -1 critical exchangeable-K requirement for most crops is (0.41 Cmolckg soil), while an -1 exchangeable K value of 0.30 Cmolckg soil was adopted by Ajiboye and Ogunwale (2013). In addition, Darryl et al. (2004) suggested that the critical exchangeable K requirement of the -1 soils for good crop yield was (0.27 Cmolckg soil), the value was also higher than 0.05 -1 Cmolckg soil exchangeable K content of these soils, suggesting that the exchangeable K levels of these soils was deficient for crop production. The non-exchangeable K in the soils -1 ranged from 0.01 to 0.29 Cmolckg soil and were low in according to Srinivasarao et al. -1 (2007) proposed ( 0.8 Cmolckg soil ) content in reserve K. Highly significantly (p ≤ 0.001) -1 affected by land uses and locations interactions, whereas the highest ( 0.29 Cmolckg soil ) was observed under enset coffee complex as compared to crop land, that might be also due to the weathering action of soil minerals and release of K from residues and vegetation debris, set free to soil solution which can in turn enter the inter lattice spaces. This result agree with Raheb and Heidari.(2011) who reported that non-exchangeable K value ranged from 39.8 to 696.9 mg kg-1 for paddy and non paddy soils of Lebanese soils, and 50 to750 mg kg-1 for mineral soils Ajiboye and Ogunwale (2013). The KSP soils ranged from 0.20 to 1.06 % and were low in accordance with the rating of FAO-UNESCO (1997). Significantly affected by land use and locations, the highest (1.06 %) was recorded under enset coffee land as compared to grazing land, which might be that cations are held on the clay and organic matter, replaced 7

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by other cations, they are exchangeable and the total number of cations can hold is related to its negative charge and constitutes the soil cation exchange capacity.

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Table .2 Distributions of potassium forms of the soils as influenced by locations and land uses

Sodo Zuria Damot Gale (n=48) Damot Sore Boloso Sore Potassium Land use Land use Land use Land use LSD Forms Means CV (5%) -1 (%) (CmolCkg ) EncL CL GL EncL CL GL EncL CL GL EncL CL GL

H2O – K 0.33 0.15 0.13 0.42 0.16 0.10 0.17 0.12 0.04 0.28 0.23 0.13 0.17 9.42 0.01 0.28 8.37 0.02 NH4OAC – K 0.50 0.31 0.27 0.61 0.23 0.14 0.35 0.17 0.17 0.39 0.27 0.18

HNO3 – K 0.40 0.24 0.19 0.48 0.23 0.15 0.27 0.16 0.14 0.32 0.28 0.22 0.25 7.00 0.01

Exch- K 0.17 0.16 0.14 0.19 0.07 0.04 0.18 0.05 0.13 0.11 0.04 0.05 0.11 9.29 0.01 Non exch- K 0.23 0.08 0.05 0.29 0.16 0.11 0.09 0.11 0.01 0.21 0.24 0.17 0.14 8.88 0.04 K– Saturation ( %) 0.77 1.06 0.82 0.95 0.46 0.23 0.78 0.25 0.54 0.47 0.20 0.23 0.57 5.85 0.01

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3.3. Thermodynamic parameters of the soils

The thermodynamic determinant used to evaluate the levels of potassium in soils included Woodruff energy of replacement, activity ratio and ionic activity. The values of the ionic strengths of potassium in the soils ranged from 0.001419 to 0.007095(μ) molL-1 were tabulated as shown (Table 3). The highest ionic strength was 0.007095(μ) mol L-1 under enset coffee land as compared to crop and grazing lands, which might be an indication of NH4AOc-extractable K for crop yields in the soils existed in active form in the soil solution. Similarly, Al-zubaidi et al (2008); Kenyanya et al. (2015) reported in Iraqi soils. The potassium activity ratio (ARK) of the soils were tabulated as shown in (Figure 3) ranged from 0.04 to 0.43 (molesL-1)1/2. Highly significantly (P ≤ 0.001) affected by the interaction effects of land uses and locations (Table 3) whereas the highest (0.43 (molesL-1)1/2 was observed under enset coffee as compared to crop land could be attributed to differences in the concentration of equilibrating solutions, the Ca and Mg contents, and probably due to the differences in the mineralogy of the soils. According to Abaslou and Abtahi (2008) found that the soils having higher K fixation capacity had exchangeable Ca varying from 77 to 92 % of the exchange complex. The suggested mechanism of K fixation is by emplacement of K between basal clay surfaces where it fits into the hexagonal cavities formed by tetrahedral oxygen of 2: 1 type of clay mineral. The value of the ARK obtained in the study was lower than those reported by Ano et al. (1995) which fall within the range of 0.09 to 3.02 (molL-1)0.5 in some Nigerian soils. However, this can lead to rapid losses of K through leaching. The free energy of replacement (ΔF) of the soils varied from - 2076.6 to -323.83 cal.mol-1, where the upper value (- 2076.6 cal.mol-1) indicates K sufficiency, and the lower (-323.83 cal.mol-1) K deficiency in accordance with the rating of Woodruff (1995), this is might be attributed to intensive cropping, fertilizer application, moisture content and organic matters accumulation variation under different land use types. This result is in agreement with that of Kenyanya et al. (2015) ranged from -3632 to -3523 cal.mol-1 in some agricultural soils of Nyamira, Kenya. Equilibrium activity ratio of the soils ranged from 0.049 to 0.074 (molL-1)1/2 and was lower in according to Yawson (2011) the suggested values (0.02 to 0.12 molL−1)½. It was highly significantly (p ≤ 0.001) affected by the interaction effects of land uses and locations (Table 3) whereas the highest (0.074 (molL-1)1/2 was observed under grazing land as compared to crop land could be attributed to greater K release into soil solution because these soils contain comparatively high amount of exchangeable calcium and magnesium values which intern increase the AReK value. Similarly, Samadi (2006) was reported at different workers. The potential buffering capacity in the soils ranged from 0.80 to 2.0 cmolkg−1/ (mol L−1)1/2 showed in (Table 3). Highly significantly (p ≤ 0.001) affected by the interaction effects of land uses and locations where as the highest (2.0 cmolkg−1/ (mol L−1)1/2 was observed under crop land as compared to enset coffee could be attributed to lowest amount of clay content, and highest amount of clay content and CEC, respectively. The values of PBCK observed in both land use indicated low potassium supplying capacity of these soils and frequent fertilization for optimum crop yield. Consequently, low PBCK indicates that ARK, K- intensity in the soil solution and hence availability of K to plants will drop rapidly when the soils are cultivated. This result was in agreement with that of Hosseinpournda Kalbasi (2002) observed that soils with the greatest PBCK values were characterized by the lowest percentage of K saturation, indicative of greater potential to replenish K concentration in soil solution. The change in −1 exchangeable potassium (±ΔK) ranged from 0.05 to 0.31 CmolCkg (Table 3 and Figure 3). Highly significantly (P ≤ 0.001) affected by the interaction effects of land uses and locations where as highest (0.31 cmolkg−1) was observed under crop land as compared to enset coffee land could be attributed to differences in equilibration analysis that these values also increased at increasing

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concentrations of the equilibration solutions. However, the values are lower than who reported by Yawson (2011) ranged 1.30 to 1.33 at Ghana soils

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Table.3. Thermodynamic parameters of the soils as influenced by locations and land use types

)

) -

)

1/2

)0.5]

−

)

−

[cmolkg

(x10

γK

)molL

(x10

cal.mol

] ]

±ΔK

ARe

(x10

(Ca + Mg) + (Ca

Location

Land use Land

(Ca+M g (Ca+M

(molL

(cmolkg

(molL

[K ΔF)

γ γ

(

− PBC Sodo Enset coffee 0.001935 6.76 0.9506 0.43 6.42 0.817 0.22 -896.71 0.09 0.072 1.26 Zuria Crop land 0.006837 7.10 0.9078 0.21 6.44 0.294 0.04 -1906.32 0.31 0.074 1.75 Grass land 0.005418 8.32 0.9183 0.25 7.64 0.400 0.38 -571.10 0.12 0.071 1.48 Damot Enset coffee 0.001419 7.66 0.9569 0.49 7.32 0.931 0.24 -842.20 0.05 0.062 0.80 Gale Crop land 0.004128 7.57 0.9274 0.29 7.02 0.435 0.33 -323.83 0.11 0.069 1.59 Grass land 0.005547 8.14 0.9164 0.24 7.45 0.336 0.41 -528.03 0.10 0.074 1.35 Damot Enset coffee 0.002709 7.85 0.9410 0.37 7.38 0.592 0.30 -713.03 0.10 0.066 1.51 Sore Crop land 0.004257 7.22 0.9264 0.29 6.68 0.555 0.29 -733.10 0.11 0.066 1.66 Grass land 0.002967 7.53 0.9382 0.36 7.06 0.612 0.29 -733.10 0.11 0.071 1.54 Boloso Enset coffee 0.007095 7.65 0.9061 0.20 6.93 0.360 0.43 -2076.6 0.11 0.064 1.71 Sore Crop land 0.005547 8.13 0.9164 0.24 7.45 0.312 0.38 -573.03 0.09 0.049 2.00 Grass land 0.006708 7.00 0.8978 0.21 6.28 0.336 0.34 -693.61 0.12 0.067 1.79 Means 0.004547 6.19 0.92 0.29 7.00 0.49 0.30 -884.1 0.11 0.07 1.53 CV (%) 6.60 7.57 1.12 9.54 6.25 6.22 7.65 -30.68 9.20 6.57 7.59 P value <0.001 0.0610 <0.001 <0.001 0.210 <0.001 <0.001 0.002 <0.001 <0.001 <0.001

LSD (5%) 0.001 NS 0.008 0.04 NS 0.10 0.06 272.92 0.03 0.001 0.09 + I= Ionic strength, ARe k (molL−1)1/2 =equilibrium activity ratio; PBCK: potential buffering capacity [cmolkg−1/(molL−1)0.5,[K ] = K concentration (mol -1 a -1 a 2+ 2+ L ), γK = activity coefficient of K , K = activity of K(mol L ) , γCa + Mg = activity coefficient of Ca+ Mg, (Ca + Mg ) = activity of Ca + Mg, ARK = activity ratio of K ,± ΔK = gain/loss of K (cmolkg−1),NS= non significant

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0.25

0.2 R² = 0.84 SZ Ensect coffee 0.15

R² = 0.77 DG Ensect coffee

0.1 R² = 0.9751 DS Ensect coffee

0.05 Quantity R² = 0.9647 BS Ensect coffee 0 0 0.2 0.4 0.6 -0.05 Intensity (ARK) -0.1

0.3 0.25 R² = 0.866 SZ Grazing 0.2 R² = 0.9174 0.15 DG Grazing R² = 0.9698 0.1

Quantity DS Grazing R² = 0.9774 0.05 0 BS Grazing -0.05 0 0.2 0.4 0.6 Intensity (ARK) 0.3 0.25 R² = 0.9417 SZ Crop 0.2 R² = 0.9473 DG Crop 0.15 0.1 R² = 0.9563 DS Crop

Quantity 0.05 R² = 0.9563 BS Crop 0 -0.05 0 0.1 0.2 0.3 0.4 0.5 -0.1 Intensity (ARK)

SZ=Sodo Zuria,DG=Damte Gale, DS=Damote Sore, and BS=Boloso Sore Figure 3. The quantity-intensity isotherms of the studied soil samples

3.4.Correlation between soil properties and soil potassium forms

The correlation analysis indicated that soil pH is significantly positive correlation with exchangeable Mg2+ and K+, and CEC (r = 0.98***, r = 0.98***; r =0.96**), respectively but negatively correlated with exchangeable Ca (r = -0.22).The CEC positively and significantly correlated with clay (r = 0.97***); OC (r = 0.96***) (Table 4). The positive and highly significant correlations of H2O-K with the clay (r = 0.83**) fraction. However H2O-K has negative and significant correlation with soil pH (r = -0.17*) and positively correlated with exch-K (r=0.13); non-exch-K (r=0.40). Also, the correlation coefficients between NH4OAC- K and exchangeable K, clay content and CEC of the studied soils were positively

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significant ( r = 0.96***; r =0.98*** ; r = 0.98***) respectively, exchangeable K with clay content (r = 0.95***) was correlated positively and OC was positively and significantly K correlated with NH4OAC-K (r = 0.95***), exchangeable-K (r = 0.95***), and AR (r = 0.95***) (Table 4) which is very much expected because of the fact that higher content of OC in the soil leads to higher CEC resulting in higher adsorption of the cations including K. Table 4. Linear coefficients of correlation between potassium forms and quantity-intensity parameters

K K H2O-K NH4OAC HNO3 Exchangeable Non AR ΔK PBC -K -K -K exchangeable K Sand -0.05 -0.98 -0.02 -0.98 -0.23 -0.95 0.24 -0.27 Silt 0.23 -0.43 -0.22 -0.43 -0.10 -0.4 -0.12 -0.11 Clay 0.05 0.98*** 0.02 0.98*** -0.23 0.95*** -0.24 -0.27

pHH20 -0.17 -0.13 -0.15 0.13 0.40 0.13 0.34 -0.14 OC 0.50 0.95*** 0.02 0.95*** -0.23 0.95*** 0.24 -0.27 Ex.K 0.11 0.96*** 0.004 0.96*** -0.24 0.96*** 0.38 -0.27 Ex.Ca 0.56** -0.22 -0.03 -0.22 -0.04 -0.22 -0.08 -0.13 Ex.Mg 0.11 0.96 0.004 0.96 -0.24 0.96 0.38 -0.27 Ex.Na 0.01 -0.33 0.12 -0.33 -0.11 -0.33 0.01 0.17 CEC 0.10 0.98*** 0.01 0.98*** -0.27 0.98*** 0.38 -0.27

4. Conclusions The present study revealed that land use types significantly affecting of the soil properties and potassium forms in the study areas to determine the potassium statues and dynamic in relation to soil properties. The results demonstrated that of the different land use types of the wolaita of southern Ethiopia have also controlled the chemical properties of the soils, particularly OC and exchangeable bases, and NH4OAC-K concentrations in the soils were positively influenced by increasing clay, CEC and exchangeable K, whiles low soil pH and high exchangeable acidity negatively affected K availability in the soils. Accordingly, crop land the lowest concentration of exchangeable base, while enset- coffee land had the highest rate of exchangeable base as well as OC. However, crop land soils were low in OC, TN and available P. Therefore, reducing intensive cultivation and integrated plant nutrient management should be employed to ameliorate deficient nutrients and enhance sustainable crop production. The enset coffee soils had higher K intensity but lower K quantity as compared to the crop lands. However, this high K intensity can be rapidly depleted through + leaching and plant uptake. Hence further, the results confirm that higher K intensity and K activity lead to a lower PBC which is a better indicator of the ability of soil to maintain K intensity. In all, considering the values of K-potential and the free energy of exchange, land use systems have a high capacity to supply K but the crop lands have a higher capacity to

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replenish the solution K. The varying properties, potassium status, and land use types of soils identified in the study areas provide adequate information to design soil potassium management options and further researches on the soils of the each site Acknowledgements We acknowledge the staff members of Department of Plant Science, Wolaita Sodo University and Hawassa Research Center of Soil Laboratory, for providing us with the necessary support to conduct this study. Funding This work was supported by Ethiopian Ministry of Education and Wolaita Sodo University. References Abaslou, H., Abtahi, A. 2008. Potassium quantity-intensity parameters and its correlation with selected soil properties in some soils of Iran. Journal of Applied Sciences. 8(10) Ajiboye,A.G.,Jamiu,O.,Azeez and Akinwande, J., Omotunde. 2015 Potassium forms and quantity intensity relationships in some wetland soils of Abeokuta, Southwestern Nigeria. Archi.Agro. and Soil Sci., 61(10): 139-140. Alemayehu, Kiflu., Sheleme, Beyene. 2013. Effects of different land use systems on selected soil properties in South Ethiopia. Journal of Soil Science and Environmental Management, 4(5):100-170 Al-Zubaidi, A., Yanni, S., Bashour, I. 2008. Potassium status in some Lebanese soils. Lebanese Science Journal, Vol. 9 (1), 81-97. Al-Zubaidi,A .2003. Potassium status in Iraqi soils. Proceedings of the regional workshop:“Potassium and water management in West Asia and North Africa, Edited by A.E.Johnston, International Potash Institute, pp. 129 – 142. Ajiboye, GA., Ogunwale, JA. 2013. Forms and distribution of potassium in particle size reactions on talc overburden soils in Nigeria. Archives of Agronomy and Soil Science, 59:2, 247-258 Ano, A.O., S.O. Ajayi ., E.S, Udo.1995. Potassium Q/I relations of Eastern Nigerian Soils developed from diverse parent materials. J. Potassium Res, 11(1): 23-29 Ayele, T. 2013. Potassium Availability under Banana- Based Land Use Systems in Abay Chamo Lake Basin, South-west Ethiopia. International Journal of Scientific Research and Reviews, 2(2): 94 Bray R.H., L.T, Kurtz. 1945. Determination of Total Organic and Available Phosphorus in soils. Soil Sci., 1945. 59: 39-45. (Chapter,4). Chapman, H.D.1965. Cation exchange capacity by ammonium saturation. 891-901.In: Black, C.A., Ensminger, L.E. and Clark, F.E. (Eds). Method of soil analysis. American Society of Agronomy. Madison Wisconsin, USA. Darwish, T., Nasri, T., El Moujabber, M., Atallah, T. 2003. Impact of soil nature and mineral composition on the management and availability of potassium in Lebanese soils. Proceedings of the Regional Workshop: “Potassium and water management in West Asia and North Africa.” Edited by A.E. Johnston, International Potash Institute, pp.152– 160. Darryl, W., Jon, D Lee J, Carrie L. 2004. Nutrients Recommendation for Field Crops in Michigan. Extension Bulletin E2904. Department of Crop and Soil Sciences Michigan State University Day, P.R. 1965. Hydrometer method of particle size analysis. pp. 562-563. In: C.A. Black (Ed.). Methods of Soil Analysis. Agronomy. Part II, No. 9. American Society of Agronomy, Madison, Wisconsin, USA. FAO-UNESCO. 1997. FAO-UNESCO soil map of the world. Revised legend with correction and updates. Technical paper 20, ISRIC Wageningen George, R.,Michael, S. 2002. Potassium for crop production. University of Minnesota Extension. (800), 876-8636.

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