Fertilizer Type, But Not Time of Cessation of Irrigation, Affect Onion Development and Yield in a Semi-Arid Region

Onion production is limited by environmental factors, especially in arid and semi-arid regions. A two-year study was carried out to investigate the response of onion (Allium cepa L.) cv. Bawku Red to the application of farmyard manure (FYM), inorganic fertilizer (IF) or a combination of manure and inorganic fertilizer (FYM+IF) when irrigation is withheld just before breakover or at 50% breakover. Onion plant height, foliage weight, bulb diameter and bulb weight were increased by FYM+IF in both years. Onion bulb yield due to the FYM+IF treatment was 34.1% higher than that for FYM, and 4.6% higher than that for the IF treatment. The highest number of split bulbs, which are not marketable but are used by producers under our economic conditions, was recorded for FYM+IF plots (mean for two years, 6800 bulbs/ha) with FYM recording the lowest (mean for two years, 1100 bulbs/ha). Application of FYM either alone or in combination with IF significantly (P < 0.05) reduced bulb rot. The percentage of marketable bulbs was not different among treatments. Neither time when irrigation was withheld nor the interaction of nutrient × time when irrigation was withheld affected onion growth and bulb yield. Thus, application of both FYM+IF at half their recommended rates increased onion bulb yield and reduced field defects.