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

Effect of nitrogen fertilization and irrigation on yield and quality of broccoli was studied in field experiments conducted in 1997-1999. Broccoli for autumn harvest was grown under natural precipitation only or with irrigation when soil moisture dropped to the level at which soil suction exceeded 30 kPa. In applied nitrogen rates of 100, 200, 400 and 600 kg N(.)ha(-1) the amount of residual nitrogen in the soil layer of 0-60 cm has been included. Nitrogen rates of 200, 400 and 600 kg N(.)ha(-1) were applied either as single preplant only or as split application, while the rate of 100 kg N(.)h(-1) as preplant only. Irrigation and higher rates of nitrogen (400 and 600 kg N(.)ha(-1)) increased the plant weight and the yield of broccoli, as well as hastened the head formation and harvest time. Split applications did not increase the yield, when sidedressing was preceded by high preplant rates of nitrogen (300 and 500 kg N(.)ha(-1)), was however advantageous at low preplant rate (100 kg N(.)ha(-1)). Optimum range of nitrate nitrogen content in the soil, 25 days after planting, was 209-297 mg(.)l(-1) when irrigation was applied and 112-204 mg(.)l(-1) for natural precipitation only. For split application of nitrogen the optimum range was lower (88-179 mg mg(.)l(-1)) and was the same as well for irrigated as nonirrigated 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 nitrogen fertilization the contents of sugars increased but the level of ascorbic acid and dietary fiber dropped. The contents of nitrates in broccoli heads increased too, when high nitrogen rates were applied. Irrigation lowered the contents of nitrates, whereas the level o sugars, ascorbic acid and beta carotene did not change as compared to broccoli from non irrigated treatments.