Influence of sulfur, calcium and magnesium supplementation on the post-harvest and storage quality 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, poor soil nutrient management, and high post-harvest losses, which affect 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 pests and diseases, onion bulb firmness and prices/kg. Normality, regression, and chisquare 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. All onion varieties at all treatments in site 1 reported few incidences of onion chafer grub pest attacks and rot disease, with 0 reported cases across most plots. "Texas Grano” yellow onion variety bulbs were more stable at S, Ca&Mg application at 60kg/ha with 0.39g weight loss after two weeks of curing. “Texas Grano” yellow onion at S, Ca&Mg@40kgs/ha reported the highest gross market prices of KES 180/kg with 15 onions due to reduced pest and disease incidences, as well as firm bulbs. Correlation analysis was also performed, and a weak relationship of 13.7% was found between bulb firmness and the gross market prices/kg. Therefore, based on the results, this research study concluded that the use of sulfur, calcium, and magnesium supplements significantly increases onion growth, yield, and bulb development, and significantly increases onion production and marketability. 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.