Effects of fertilisation and irrigation practices on yield, maturity and storability of onions

Abstract

The study aimed to establish whether a high onion yield and good storage performance could be obtained with low fertilisation rates if irrigation was applied when necessary. Two-year experiments investigated the effects of three NPK fertiliser levels (N 50, 100, 125/150 kg/ha), with and without irrigation, on yield, advancement of maturity, storage losses and shelf life. High fertilisation advanced maturity but irrigation had no effect. High fertilisation increased yield only in 1996 (5-7%), but irrigation increased the yield noticeably: by 33.5% in 1995 and 8.5% in 1996. There was no interaction between fertilisation and irrigation. The low fertilisation optimum is attributed to the mineralisation of soil nitrogen, as the soil was rich in organic matter. At the low fertilisation level, plants took up twice as much nitrogen as present in the fertiliser, and with increased fertilisation the nitrogen uptake increased markedly. The foliage nitrogen content was low, evidently as a result of late harvesting. Treatments had only a minor effect on the storage performance and shelf life of onions. The results suggest that fertilisation rates could be reduced in onion production. Irrigation during warm and dry periods is essential to achieve the maximum yield potential and does not impair the storage quality of onions.