Seasonal plant growth, leaf and bulb mineral nutrients, and bulb yield and quality under chemical, mixed, and organic fertilization in sweet onion (Allium cepa L.)

The utilization of organic fertilizers is of growing interest to improve soil quality and increase environmental sustainability. There is, however, limited information on the use of organic fertilizers for sweet onion production. The objective of this study was to evaluate the effects of chemical, mixed, and organic fertilizers on plant growth, bulb yield and quality, and mineral nutrients of sweet onion. The study was conducted at the Horticulture Farm, Tifton Campus, University of Georgia, in the winters of 2013, 2014 and 2017. The experimental design was a randomized complete block with three fertilizer treatments and four replications. Fertilizer treatments consisted on the application of Chemical (100% N), Mixed [chemical (50% N) + organic (50% N)] and Organic (100% N) fertilizers. In all treatments, the crop received a total of 150 kg center dot ha(-1) N. Plants in the Organic treatment showed augmented root growth and decreased leaf nitrogen compared to the Chemical and Mixed treatments. There were no differences in mean seasonal shoot and bulb dry weights and root-to-shoot ratio among treatments. Fertilizer treatments also had no impact on marketable and total bulb yields, bulb concentrations of macro and micronutrients, bulb disorders and diseases, and bulb chemical composition. Shoot and root growth increased with increasing air temperature, which explains the reduced plant growth during the winter. In conclusion, sweet onion grown with organic fertilizer alone or mixed (50% organic N + 50% inorganic N) produced plants and bulb yields and quality comparable to those grown with chemical fertilizer.