Potassium quantity and intensity variations of soils under anaerobic condition in relation to their mineralogical properties

A. R. Ahmad and A. B. Ismail

Abstract

Two soils with different mineralogical characteristics were subjected to anaerobic condition and their quantity-intensity variations were monitored with time up to 45 days. Selangor series with an appreciable amount of 2:1 clays showed higher capacity for exchangeable K (ΔK_E.) as compared with Sendong series which had only very small amount of 2:1 clay. At the onset of reduction the quantity-intensity variation indicated that negative charges were exposed when Fe-surface complex dissolved. This increased the exchange capacity for K as shown by the increase in ΔK_EO and decrease in CR_KS. Longer anaerobic condition could reduce the octahedral Fe³⁺ to Fe²⁺ The redistribution of negative charges in the layer lattices of the 2:1 clays could enhance the fixation of K by layer collapse or adsorption of K on higher energy sites on the clay surfaces. This is indicated by the decrease in CR_KS, and ΔK_EO values. With further reduction, Fe or Al hydroxides polymers could form in the interlayer position of the clays which released more K to the exchangeable sites (indicated by the reversal of the shift of the quantity-intensity curves with the increase in CR_KS. and ΔK_EO).

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