Abstract
Aim of the study: Firstly, to evaluate the K dynamics of soils through a quantity-intensity isotherm study; and secondly, to characterize the soils on the basis of quantity-intensity (Q/I) parameters.Area of study: Gazipur, BangladeshMaterial and methods: Eleven soils collected from major agro-ecological zones in Bangladesh were evaluated for their varying K dynamics parameters, and K supplying capacities of these soils were described.Main results: The Q/I plot showed both linear and polynomial relationships for soils in the study. The eleven soils had labile K ranging from 0.022 in Palashbari clay loam to 1.35 cmol kg-1 in Barisal clay. The latter soil had the highest equilibrium K activity ratio (0.003 mol L-1)1/2 and potential buffering capacity (PBC) (460.4 (cmol kg-1) (mol L-1)1/2). The PBC of soils for non-exchangeable pool (PBCne) was much higher than that of exchangeable pool (PBCe) in most soils. The largest amount of PBCne and PBCe occurred in Barisal clay, Gopalpur clay, Jhalokathi clay and Nachol loam which had a higher K desorption rate than all the other soils. The equilibrium exchangeable K, critical exchangeable K and equilibrium solution K of the soils varied widely (0.0006-0.035, 0.06-0.61 and 0.06-0.604 cmol kg-1, respectively). The added K was converted almost equally for the respective soils, with specific reference to the respective exchangeable and non-exchangeable pool for Barisal clay and Nachol loam.Research highlights: All the studied parameters revealed wide variations among the soils. The linear and polynomial relationships for soils can efficiently characterize intensively cultivated soils in Bangladesh.
Highlights
Crops take up abundant amounts of potassium (K) from soils, which is buffered by rapidly exchangeable forms of K
Different soils show the same value of activity ratio for K (ARK) and may not possess the same capacity for maintaining ARK while K+ is removed by plant roots (Beckett, 1964a)
The samples were collected (February, 2011) from intensively crop cultivated farmers’ fields, which are considered as being representative of the particular location under certain agro-ecological zones (AEZ)
Summary
Crops take up abundant amounts of potassium (K) from soils, which is buffered by rapidly exchangeable forms of K. The ammonium acetate (NH4OAc) extraction method of K which is undertaken in some countries including Bangladesh (Saleque et al, 2009; Islam et al, 2017), cannot generate enough K to satisfy crops, because this reagent may extract only exchangeable portion of K, which is mostly pH dependent This method may not properly determine the level of exhaustion of soil K involving crops, and deficiency increases in soils under rice-based intensive cropping systems. Different soils show the same value of activity ratio for K (ARK) and may not possess the same capacity for maintaining ARK while K+ is removed by plant roots (Beckett, 1964a) These findings brought about the classic Q/I curves where the ratio of aK/(aCa + aMg)1/2 is linked to the change in exchangeable K+ so that the effect of quantity (exchangeable K) on intensity can be documented. The objectives of this experiment were to: (i) study the K dynamics of soils through quantity-intensity isotherm studies; and (ii) characterize the soils on the basis of Q/I parameters so that K fertility management under intensive crop cultivation is better understood
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