Effects of Different Rates of Potassium Application on Growth and Yield of Soybean

Abstract

Soybean is an important legume crop valued for its high protein and oil content, but its productivity is often limited by poor soil fertility and environmental stresses. This study aimed to determine the optimum potassium application rate for improving soybean growth and yield under the agroecological conditions of Kabul, Afghanistan. A field experiment was conducted during the 2025 growing season at the Research Farm of the Faculty of Agriculture, Kabul University, using a randomized complete block design with five potassium levels (0, 25, 50, 75, and 100 kg ha⁻¹) and three replications. Standard agronomic practices were applied uniformly throughout the experiment. Data were collected on plant height, branches per plant, pods per plant, total seeds per plant, 100-seed weight, and grain yield, and analysed using STAR software with the least significant difference test at the 5% probability level. Potassium application had no significant effect on vegetative growth traits, including plant height and number of branches per plant. However, it significantly improved yield components and grain yield. The application of 75 kg K ha⁻¹ produced the highest number of pods per plant, greatest 100-seed weight, and maximum grain yield, whereas increasing the rate to 100 kg K ha⁻¹ resulted in reduced yield. The findings indicate that potassium application enhances soybean productivity primarily through improved yield components rather than vegetative growth. It is concluded that 75 kg K ha⁻¹ is the optimum potassium rate for maximizing soybean yield under the agroecological conditions of Kabul, Afghanistan.