Effect of varying rates and combinations of sulfur, calcium and magnesium supplementation on the growth, yield and bulb development of onions for increased production and marketability in Kenya

Abstract

Onion (Allium cepa) is a vital crop in Kenya, both in the diet due to its nutritional health benefits as well as its economic gains. However, the potential of onions as a functional food is limited due to suboptimal agronomic practices and poor soil nutrient management, which affect its production and marketability. Therefore, this research aimed to investigate the effects of sulfur, calcium, and magnesium supplementation on the growth, yield, and bulb development of onions to increase production and marketability. The research adopted RCBD in two sites in Kenya: Kisaju-Kajiado County and Koma-Machakos County. Experimental treatments included varying levels of sulfur, calcium, and magnesium supplementation and their combinations at different levels in onions and their effects were evaluated towards the bulb weight/scallion biomass, bulb diameter and onion profitability. Normality, regression, and chi-square preliminary tests were performed on the data using SPSS software and the data were found to be parametric. ANOVA tests were then performed, and where significant differences were found, post-hoc tests were performed. Onions subjected to treatment of S, Ca&Mg@40kgs/ha reported the highest gross market prices, at KES 180/kg, due to the high bulb weight and scallion biomass, measured as an average of 15 onions on the "Texas Grano" variety. Ca&Mg@30kg/ha had the highest bulb diameter with 42.6mm. The Kisaju-Kajiado site had the highest general performance and profitability, with net returns of KES 76.94/kg on average, with the "Red Creole" variety having the highest at S, Ca&Mg@40kg/ha, with net returns of up to KES 77.44/kg on average. Correlation analysis was also performed, and a strong relationship of 95% was found between bulb weight and scallion measure and the market prices/kg. Therefore, based on the results, this research study concluded that the use of sulfur, calcium and magnesium supplements significantly boosts onion growth, yield and bulb development, increasing the production and marketability of onions in turn. The study contributes to improving onion production and yield, as well as the crop's economic value, to address food security. The findings are therefore beneficial to onion farmers, policymakers, and other key stakeholders in the field of agriculture.