Potassium-use efficiencies and economic optimization as influenced by levels of potassium and soybean (Glycine max) genotypes under staggered planting

Abstract

Field experiments were conducted during 2006-07 to study the effect of planting time and potassium levels on productivity, potassium uptake and potassium-use efficiency by promising soybean (Glycine max L. Merr.) genotypes under Malwa plateau of central India. Timely planting of soybean (last fortnight of June) showed superiority over the late planting with respect to all the parameters evaluated. Timely planting of soybean gave higher yield (20.28%) and potassium uptake (24.62%) over late planting. Potassium recovery, physiological and internal-use efficiency were higher in late planted soybean compared with the timely planting. The significantly highest net returns was recorded with 49.8 kg K/ha, while the maximum B:C ratio was associated with 33.2 kg K/ha. Potassium uptake increased concomitantly with the levels of potassium. Potassium-use efficiencies (agronomic, recovery efficiency, physiological efficiency and internal K use efficiency) decreased as the levels of potassium increased. All the 3 soybean genotypes were found to be identical in terms of productivity potential while soybean genotypes differed significantly among themselves with regards to potassium-use efficiencies. The economic optimum level of potassium for planting time and soybean genotypes ranged from 37 to 39 kg/ha. Variety like 'NRC 7' has immense utility when planting is delayed.