Relationship between K/Ca Ratios in the Soil Solution with the Dynamic of K in Ultisol and Vertisol of Upland Area

Abstract

The objectives of this experiment were: (I) to study the effect of K and Ca fertilization on the dynamic of K, (2) to study the relationship between the dynamic of K in the soils with corn growth, and (3) to determine the optimum K requirement on diflerent K/Ca ratio in the soil solution. Ultisol and Vertisol from upland area were used for the study. The determination of K and Ca dosage was based on the maximum soil sorption. The experiment was carried out in greenhouse using the factorial randomized complete design with three replications. Four levels K dosage and three levels Ca dosage were applied in the experiment. The C-7 hybrid of corn was selected as indicator plant. The result showed that adding of K and Ca increased the dry weight of plant in both Ultisol and Vertisol. In Ultisol, adding of K increased the amount of exchangeable Ca, Mg and K, and water-extracted K, whereas adding of Ca increased the exchangeable Ca and Mg and water-extracted K. The optimum K requirement for Ultisol was 58 mg kg-' for K/Ca ratio <0.03 and 88 mg kg-' for K/Ca ratio >0.03. In Vertisol, adding of K increased the exchangeable and water-extracted K, while adding of Ca increased both exchangeable and water-extracted Ca and Mg. The optimum K requirement was 55 mg kg-' for K/Ca ratio c0.03 and 171 mg kg-' for K/Ca ratio >0.03. Waterextracted Ca and Mg showed a negative relationship with K/Ca ratio both in Ultisol and Vertisol. Positive rejutionship between K/Ca ratios with water-extracted K was found in Ultisol, and with both exchangeable and water-extracted K in Vertisol. The increasing of WCa ratio increased the critical level of exchangeable K and water-extracted K.