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

The study aimed to establish whether a hi,oh onion yield and good storage p erformance could be obtained with low fertilisation rates if irrigation was applied when necessary. Two-year experiments investigated the effects of t hree NPK fertiliser levels (N 50, 100, 125/150 kg/ha), with and without irr igation, on yield, advancement of maturity, storage losses and shelf life. High fertilisation advanced maturity but irrigation had no effect. High fer tilisation increased yield only in 1996 (5-7%), but irrigation increased th e yield noticeably: by 33.5% in 1995 and 8.5% in 1996. There was no interac tion 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 mu ch nitrogen as present in the fertiliser, and with increased fertilisation the nitrogen uptake increased markedly. The foliage nitrogen content was lo w, evidently as a result of late harvesting. Treatments had only a minor ef fect on the storage performance and shelf life of onions. The results sugge st that fertilisation rates could be reduced in onion production. Irrigatio n during warm and dry periods is essential to achieve the maximum yield pot ential and does not impair the storage quality of onions.