The effect of nitrogen fertilization and irrigation on yield and quality of broccoli.

摘要

The effect of N fertilization (at 100, 200, 400 and 600 kg N/ha) and irrigation on yield and quality of broccoli was studied in field experiments conducted in 1997-99 in Poland. Broccoli for autumn harvest was grown under natural precipitation onlyor with irrigation when soil moisture dropped to the level at which soil suction exceeded 30 kPa. The amount of residual N in the soil layer of 0-60 cm was included. N at 200, 400 and 600 kg N/ha were applied either as single preplant only or as split application, while 100 kg N/ha as preplant only. Irrigation and higher rates of N (400 and 600 kg N/ha) increased plant weight and yield of broccoli and hastened the head formation and harvest time. Split applications did not increase the yield when sidedressing was preceded by high preplant N rates (400 and 600 kg N/ha), but was advantageous at low preplant rate (100 kg N/ha). Optimum range of nitrate N content in the soil, 25 days after planting, was 209-297 mg/litre when irrigation was applied and 112-204 mg/litre for natural precipitation only. For split application of N, the optimum range was lower (88-179 mg/litre) and was the same as well for irrigated as non-irrigated treatments. Under the influence of irrigation and higher N rates, broccoli heads had more attractive green colour but incidence of hollow stem was expanded. With high N fertilization, sugar content increased but the level of ascorbic acid and dietary fibre dropped. The nitrate content in broccoli heads also increased when high nitrogen rates were applied. Irrigation lowered the nitrate content, whereas the sugar, ascorbic acid and beta-carotene contents did not change compared with broccoli from non-irrigated treatments.