Bulb quality of garlic (Allium sativum L.) as influenced by the application of inorganic fertilizers

Garlic is an important cash crop for smallholder farmers in Ethiopia. Bulb quality is an important attribute that adds to the use and marketability of the crop. However, garlic bulb quality is constrained by several factors in the country among which imbalanced and low availability of nutrients in the soil is prominent. Therefore, a study was conducted on two soil types (Andosol and Vertisol) with the objective of elucidating the effect of nitrogen, phosphorus, and sulphur application on the quality of the crop. The treatments consisted of three levels of nitrogen (0, 92, 138 kg N ha-1), three levels of phosphorus (0, 40, 80 kg P ha-1), and three levels of sulphur (0, 30, 60 kg S ha-1). The experiment was laid out as a randomized complete block design in a factorial arrangement with three replications on each soil type. The results revealed that the main as well as the interaction effects of N, P, and S fertilizers on both soil types significantly (P ≤ 0.05) influenced bulb quality, namely, dry matter percentage, total soluble solids, pungency, bulb protein content, and bulb weight loss in storage, and concentrations of major nutrients in the bulb tissues. The bulb quality indices studied on both soil types correlated positively and significantly with each other but had a negative correlation with bulb weight loss. This result indicates favorable effects of integrated application of nitrogen, phosphorus and sulphur on garlic bulb quality. Combined applications of 92 kg N + 40 kg P + 30 kg S ha-1 and 138 kg N + 40 kg P + 60 kg S ha-1 led to the attainment of optimum bulb quality attributes on Andosol and Vertisol, respectively. However, it was application of 92 kg N + 40 kg P + 30 kg S ha-1 that was found to be economical for farmers.   Key words: Andosol, bulb quality, inorganic fertilizer, nutrient concentration, soil type, Vertisol.