Research Projects

Potassium (K) is a major nutrient in soils whose origin, distribution and dynamics are governed by the weathering of K-bearing minerals (Fanning et al. 1989). K-feldspars, muscovite and biotite, being the principal K-bearing minerals, are present in the sand, silt and clay fractions of major soils of India (Pal et al. 2001). 1N NH4OAc extract is hitherto followed to determine soil available K. However, the available K determined by this method often shows an anomalous crop response to added K fertilizers (Das et al. 2022). This method does not extract the entire adsorbed and interlayer K present in various K-bearing minerals. Therefore, it may not adequately represent the available K for many soils (Askegaard and Eriksen 2002). This scenario is prevalent in soils of semi-arid tropical (SAT) climate (Islam et al. 2017). SAT soils of India contain reasonably high amounts of K-bearing minerals (Pal et al. 2006). The release of K in SAT soils primarily depends on the K-selectivity of the K-bearing minerals. The K released from the minerals to the soil solution is governed by mass exchange rather than diffusion, particularly in SAT soils, where precipitation is low or soil permeability is impeded (Pal et al. 2001). Therefore, to gain knowledge on the respective contribution of K from various K-bearing minerals, K release from colloidal exchange sites needs to be done using a strong exchanger like BaCl2, and a quasi-equilibrium needs to be established (Pal et al. 2001). Srinivasarao et al. (2001) suggested a greater contribution of non-exchangeable K towards plant nutrition in soils low in available K. The non-exchangeable K, when extracted by boiling nitric acid, shows a good correlation to crop response (Srinivasarao et al. 2023). But, in this method, most K is released via cation exchange and the remainder via mineral structure dissolution (Li et al. 2015). Moreover, the scientific reason for using HNO3 in preference to other mineral acids in the K release mechanism is not well explained yet. K release from K-feldspar and muscovite is insufficient to meet the crop demand at peak periods (Pal 2017). Both field experiments and experimental studies indicated that moscovite barely weathers in soils when it coexists with biotite and K availability is primarily controlled by biotite (Feigenbaum et al. 1981; Taboada and Garcia 1999; Pal et al. 2001). To characterize the nature of soil micas of Indian soils, X-ray diffraction intensity ratios are generally used (Pal et al. 2001). It is thus necessary to determine the biotite content in the presence of muscovite in soils. There is no selective quantification method of biotite content except the rigorous, repeated batch-type Ba-K exchange technique (Pal et al. 2006). Therefore, suitable methods to quantify the soil biotite content are warranted. The research outcomes will help predict the long-term K supply capacity of soils and lessen the import burden of K fertilizers, thereby saving foreign reserves.