IJA-2017_2.qxp_Hrev_master 10/07/17 10:49 Pagina 102 Italian Journal of Agronomy 2017; volume 12:818 Relationship of soil potassium forms with maize potassium contents in soils derived from different parent materials Rashid Mehmood Butt,1 Mohammad Saleem Akhtar,1 Ayaz Mehmood,2 Muhammad Imran,1 Shah Rukh,1 Ghashiya Sattar Kayani,1 Muhammad Tariq Siddique,1 Kashif Sarfraz Abbasi,3 Abdul Qayyum,2 Zahoor Ahmad2,4 1Department of Soil Science & SWC, Pir Mehr Ali Shah-Arid Agriculture University, Rawalpindi; 2Department of Agricultural Sciences, University of Haripur, Haripur; 3Department of Food Technology, Pir Mehr Ali Shah-Arid Agriculture University, Rawalpindi, Pakistan; 4Department of Agriculture and Biological Engineering, University of Florida, Gainesville, FL, USA Abstract Introduction Understanding of soil potassium (K) dynamics is essential for Potassium is a macronutrient that affects plant growth, quality sustainable crop production. Bioavailability of K depends on of grains and fruits. Potassium plays an essential role in plant forms and distribution within the soil profile. The objectives of metabolism (Ruiz and Romero, 2002). In Pakistan, most soils con- this research were to determine which soil K forms control the tain relatively large amounts of K occurring as a structural element maize (Zea mays) K contents and compare the extracting capabil- of primary minerals, i.e. K-feldspar, muscovite, biotite and illite ity of sodium tetraphenylborate (NaTPB) with ammonium acetate (Akhtar, 1989), and only aonly small fraction is present in plant avail- (NH4OAc) method. Nine soils representing three different parent able form. Availability of K is controlled by its release from K materials, i.e. loess, sandstone and shale were sampled at three bearing minerals (mica, feldspar) and fixation by partially weath- surface genetic horizons. Within each parent material, three soils ered mica and vermiculite, and high charge smectite. Potassium at varying level of development were selected. Besides basic soil release from soiluse minerals depends on their contents, types, struc- parameters, K was fractioned into water soluble K, exchangeable tural properties and particle size distribution. The structural prop- K, non-exchangeable K, and NaTPB-extracted K. The maize was erties of 2:1 type clay minerals controlling K fixation are layer sown in pots having 2 kg soil from each genetic horizon. Crop was charge density and charge location. The order of ease of K+ expul- harvested at seven weeks and plant was analysed for K contents. sion from different minerals by oxalic and citric acids is biotite > Results show that NaTPB-extracted K gave best correlation as microcline > orthoclase > muscovite (Song and Huang, 1988). compared to NH4OAc method. This conveys that a non-exchange- Soils that contain partially weathered mica, vermiculite or high able K portion that becomes available to plants can be better esti- charge smectite as the dominant clay minerals are usually low in + mated by NaTPB method than NH4OAc extraction. soil solution K. Whereas NH4 fertilisation enhances K availabili- ty as they occupy K adsorption sites in clay minerals (Kilic et al., 1999). The clay fraction also comprises kaolinite, montmoril- commerciallonite, chlorite, and vermiculite (Bajwa, 1989). The soils hav- ing sufficient amount of vermiculites and partially weathered mica have capacity to fix an enormous quantity of applied K Correspondence: Ayaz Mehmood, Department of Agricultural Sciences, (Ranjha et al., 1992). The soils of Pakistan have mixed miner- University of Haripur, Haripur University Road, 22640 Haripur, alogy. The sand and silt fractions of three Indus river basin Pakistan. Non soils, i.e. Gujranwala, Peshawar and Lyallpur comprise di and E-mail: [email protected] trioctahedral mica, quartz, feldspar and chlorite. Principal Key words: Potassium forms; Potassium availability; Parent material; minerals in clay fractions are mica, kaolinite and smectite. Soil genesis; Maize. While chlorite and quartz are also present (Akhtar and Dixon, 2009). Chemical extractants estimate the fraction of soil K that plant Received for publication: 3 August 2016. Revision received: 16 December 2016. absorbs but do not assess the natural binding strength of soil par- Accepted for publication: 17 December 2016. ticles for K or the contributive cations like calcium and magne- sium. In addition, the electrolyte concentrations of most chemical ©Copyright R.M. Butt et al., 2017 extractants used to test soil K are much higher than the soil solute Licensee PAGEPress, Italy in field soils. Consequently, these high electrolyte concentrations Italian Journal of Agronomy 2017; 12:818 cause an artificial stress on the soil system, resulting indiscrimi- doi:10.4081/ija.2017.818 nate extraction of selectively adsorbed K (Herlihy, 1992). Soil K extracted under these circumstances often misrepresents plant- This article is distributed under the terms of the Creative Commons Attribution Noncommercial License (by-nc 4.0) which permits any non- available K, since some of K remain un-extracted due to being commercial use, distribution, and reproduction in any medium, provid- non-exchangeable but would have available to plants in case of ed the original author(s) and source are credited. deficiency. The widely used chemical tests for plant available K in soils is [page 102] [Italian Journal of Agronomy 2017; 12:818] IJA-2017_2.qxp_Hrev_master 10/07/17 10:49 Pagina 103 Article pH 7, 1M ammonium acetate (Hosseinpur and Samavati, 2008). Soil potassium forms determination Ammonium acetate remains most widely used test for plant avail- Soil K was fractionated into water soluble K, exchangeable K able K in soil extracts, water soluble and exchangeable K (Cox et and non-exchangeable K. Water soluble K was estimated by al., 1999) and may cause overestimation in case non-exchangeable extracting with deionised water (Jackson, 1973). Exchangeable K K is also being extracted. Salts or dilute acids extracts lesser K was determined by extracting with 1 M NH4OAc solution than those extracted by 1 M NH4OAc method which suggests that (Knudsen et al., 1996). Non-exchangeable K was determined by the non-exchangeable K in soils cannot be evaluated with weak boiling soil in 25 mL 1.0 M HNO3. The digested residues were fil- extractants of salts or dilute acids (Simard and Zizka, 1994; tered and concentration of K was quantified on flame photometer Hosseinpur and Sinegani, 2004). Sodium tetraphenylborate can (model PFP7; Jenway, Stone, UK) using Pratt (1965) method. extract both exchangeable and non-exchangeable K better than The NaTPB-extractable K was done using the procedure as NH4OAc (Cox and Joern, 1997; Cox et al., 1999). This advantage described by Cox et al. (1999). Briefly, 500 mg soil was putted in can increase accuracy in predicting plant K uptake, especially 50 mL centrifuge tubes and mixed with 3 mL extractant (NaBPh4 when plants obtain considerable amounts of K from non- + NaCl + 0.01 mol L–1 EDTA). Mixture was shaken at 200 rpm for exchangeable forms. On the other hand, some researchers reported –1 20 min. Later, 25 mL quenching solution (0.5 mol L NH4Cl + that NaTPB has no advantage compared to the traditional methods –1 0.14 mol L CuCl2) was added to the tubes to stop the further for assessment of plant available K (Schindler et al., 2002; extraction of soil K. The tubes were heated in water bath for 60 Fernandez et al., 2008). The effectiveness of solute used for assess- min to dissolve the KBPH4 precipitates. The supernatant was sep- ment of available soil K seems largely dependent on the non- arated by centrifugation at 5000 rpm for 10 min and filtrate was exchangeable K extracting power and extraction period of the analysed for K by using the procedure described earlier. method that different researchers employed. Studies on K extrac- tion through NaTPB, and its comparison with NH4OAc extraction Pot experiment and plant potassium concentration method are very scarce. It is hypothesised that the K extracted by determination NaTPB may be the better predictor for the bioavailable K than the extracted by other extractants. We sampled soils at different level About 2 kg of the soil selected from each horizon was packed of development in three different parent materials at three depths in pots. Five uniform weightonly seeds of maize variety Kashmir gold level with the purpose of wide range of soil properties. The objec- were sown in each pot. The seedlings were thinned to two plants tives of the study were to i) assess which soil K forms controls the per pot one week after germination and irrigated with distilled de- –1 – maize (Zea mays) K contents, ii) to compare the extracting capa- ionised water. Each pot received 200 mg kg nitrogen, 50 mg kg 1 –1 –1 bility of NaTPB method with NH4OAc method and iii) to deter- phosphorus,use 123 mg kg boron, 200 mg kg zinc and 310 mg –1 mine which method is better to predict the available K using maize kg iron. Seven-week old plant was harvested, oven dried at 65°C, as a test crop. and whole plant (including root and shoot) weighed for biomass. The dry plant material was grounded to powder for elemental analysis. Dry ashing of plant material was done in porcelain cru- cibles in a muffle furnace at 550°C and ash was dissolved in Materials and methods hydrochloric acid. Aliquot was used for K determination using flame photometer (Chapman and Pratt, 1961). Site description and soil sampling Statistical analysis The study area is a part of Pothwar Plateau, and lies between Soil K extracted with different extractants, and plant K were latitude 32º 35” and 34º 09” N, and longitudes 71º 40” and 72º 59” statistically analysed by multivariate analysis of variance (SAS E. The parent materials of Pothwar Plateau commercialare loess and the version 9), where a value in depth-1 to depth-3 dependent upon residuum from sandstone and shale.