Calcium and magnesium releasing capacity of Alfisols under tea in south India

Abstract

Cobb–Douglas exponential function was employed to study the calcium and magnesium release pattern of south Indian tea soils. Calcium and magnesium releasing capacity of tea soils were studied by collecting soil samples from sixteen agro climatic zones of south Indian tea growing areas. Calcium and magnesium were extracted by repeat extraction method using 1 N ammonium acetate. The releasable calcium in the first extraction ranged between 280 and 1081 mg/kg while, releasable magnesium ranged from 33 to 126 mg/kg. The reduction in releasable calcium in the second extraction was 40–50% when compared to the first extraction almost in all the soils. The constant release of calcium was observed only after eighth extraction in most of the cases. Among all zones of south India the Coonoor zone of Nilgiris has recorded a maximum ‘a’ value and hence is least responsive to external application. The releasable magnesium decreased by about 50% in the second extraction itself which indicates that there should be regular application of magnesium otherwise it would become very much deficient. The magnesium content has become very low and almost constant in fifth or sixth extraction itself in majority of the cases. The ‘a’ value of all soils of south India can be grouped under responsive category for magnesium application, except for the Coonoor zone of the Nilgiris region. The Cobb–Douglas equation worked out for calcium and magnesium release indicated that the Latosols of south India could be grouped under highly responsive to medium responsive category towards externally applied calcium and magnesium nutrients.