Effect of nitrogen on the yield and quality of irrigated onions (Allium cepa L.) cv. Cream Gold grown on siliceous sands

Abstract

The effect of nitrogen (N), at rates up to 590 kg N/ha, on the yield and quality of Cream Gold onions grown on siliceous sands was investigated in field experiments conducted during 1987-88 (1 site) and 1988-89 (2 sites). As the rate of applied N increased there was a significant (P<0.001) increase in the fresh weight of tops harvested when the largest bulbs were 25-30 mm in diameter. Fresh weight of tops was significantly (P<0.001) correlated with final marketable yield of bulbs. Nitrogen application accelerated top senescence. Nitrogen-deficient plants had erect green tops at harvest. Marketable yield was significantly (P<0.01) increased and the yield of culls (unmarketable bulbs) was significantly (P<0.01) decreased as the rate of N increased at all sites. Nitrogen rates in the range 299-358 kg N/ha were required for 95% of maximum yield. Scale thickness increased significantly (P<0.05) and glucose and fructose concentrations decreased significantly (P<0.05) at 2 sites as the rate of applied N increased. Soluble solids and dry matter of bulbs were not affected by N. Bulb size increased as the rate of applied N increased, however, the magnitude of the effect varied between sites. Number of days to 10% sprouting during storage at 15 �_ 0.5�_C was significantly increased as the rate of applied N increased up to 40 kg N/ha at 2 sites. We have concluded that for the cv. Cream Gold grown on siliceous sands, the high rates of fertiliser N required to maximise marketable yield and bulb size were not detrimental to quality.