Effects of Potassium Application on Yield, Protein and Oil Content of Selected Soybean Varieties in Trans Nzoia County, Kenya

There is low soybean production due to poor agronomic techniques, such as sub-optimal application of fertilizer among other factors. There are limited studies on the effects of potassium fertilizer application which is crucial in productivity, quality, and drought resistance. A study was conducted at the Kenya Agricultural Livestock and Research Organization, Kitale demonstration farm to determine the effects of potassium fertilizer application on the yield and quality of soybean varieties. A 3 x 4 factorial experiment was laid down in Randomised Complete Block Design and replicated three times. The study had two factors, that is three soybean varieties (DPSB19, Gazelle and SB24) and four levels of potassium (0 [control], 22.5, 45, and 67.5 kg K2O ha-1) applied as sulphate of potash fertilizer (50% K2O) at planting, making a total of 12 treatments. Data collected included number of pods per plant, number of seeds per plant, weight of seed per plant and 1000-seed weight, grain yield, protein and oil content. Data collected was subjected to analysis of variance using Statistical Analysis System version 9.3 and significantly different means separated using Least Significance Difference at α = 0.05. Application of potassium at the rate of 67.5 kg K2O ha-1 resulted to higher number of pods per plant and number of seeds per plant at 78.97 and 243.40, and 44.47 and 141.20 in the varieties DPSB19 and Gazelle, while in SB24 higher recording of 51.23 and 162.40 was observed with 22.5 kg K2­O ha-1. The higher 1000-seed weight was recorded in 22.5 kg K2O ha-1 in DPSB19 and Gazelle varieties, while for SB24 it was recorded in 67.5 kg K2O ha-1. The highest grain yield recorded was 9156.45 kg per ha, in DPSB19 in 22.5 kg K2O ha-1, 4517. 67.5 kg per ha in Gazelle variety in 67.5 kg K2O ha-1 and 6432.78 kg per ha in SB24 variety in 22.5 kg K2O ha-1. The higher percentage oil content was observed in 45 K2O kg ha-1 in DPSB19 (28.48%) and SB24 (23.38%) varieties, and in 22.5 kg K2O ha-1 in Gazelle (19.38%) variety and the higher percentage protein content was recorded in 45 K2O kg ha-1 in DPSB19 (42.99%) and Gazelle (40.56%), and in 45 K2O kg ha-1 in SB24 (48.87%). These findings show that soybean farmers should apply potassium fertilizer for appropriate growth, increased yield, protein and oil content in different soybean varieties. It is recommended that application of potassium at 67.5 kg K2O ha-1 be done for better soybean growth, yield and protein content and application of potassium at 45 kg K2O ha-1 is done for high oil content.