Marketable and nutritional quality of leeks as affected by water and nitrogen supply and plant age at Harvest

The marketable and nutritional quality of leeks as affected by nitrogen fertilisation, water supply, and plant age at harvest was investigated during 1991 and 1992. The yield of marketable leeks increased with increasing nitrogen supply, although only small differences were observed between 160 and 280 kg total N ha -1 The total nitrogen supply includes soil mineral nitrogen within the 0-50 cm depth. The yield was lower when leeks were grown with less frequent irrigation, ie irrigation at a soil water potential of -0.09 MPa at 20 cm depth. On average, the yield of leeks increased until harvest in the middle of October, 200 days after sowing. The concentration of nitrate increased and the concentrations of dry matter and potassium decreased with increased nitrogen supply. Leeks grown with less frequent irrigation showed increased concentrations of dietary fibre, vitamin C, nitrate, protein, calcium, magnesium, and manganese. The nutritional quality of leeks improved with increased plant age at harvest because the concentration of potassium increased and the concentration of nitrate decreased.