Forms of Soil K and their Contributions to Plant K in Typic Ustipsament Loamy Sand Soil under Potato

摘要

A long-term field experiment (in progress at PAU research farm since 1992)on Typic Ustipsament loamy sand soil involving potato crop was selected to study transformations of K applied at 0,60 and 120 kg K_2O ha~(-1).Potassium application significantly increased all forms of soil K.However,percent water soluble K and exchangeable K increased,whereas,percent non-exchangeable K decreased and percent mineral K did not show any change with K application.Mineral K was the dominant K fraction followed by non-exchangeable K,exchangeable K and the least was water soluble K.Only water soluble and exchangeable K showed highly significant positive correlations with available K,tuber yield and total K uptake by potato.Regression and path coefficient analyses also indicated water soluble and exchangeable K fractions to be the dominant contributing forms,either directly or indirectly,towards available K and its subsequent utilization by potato crop.Lower energies required by potato plant to extract these two fractions from soil compared to the remaining forms substantiated the above findings.An appreciable indirect contribution of non-exchangeable K towards soil available K and total K uptake by potato indicated that non-exchangeable K controls the availability of K and its subsequent utilization by potato.