N-RESPONSE MODEL FOR VEGETABLES

Leaching of nitrogen may cause environmental problems because it is a waste of a valuable plant nutrient and because it increases the nitrate concentration of surrounding waters.

Fertilization for best economic returns and optimal nutrient use efficiency should take account of both production of dry matter, variations in N-mineralization and leaching. A model for predicting the optimum fertilizer requirement of a wide range of crops has been developed at Wellesbourne in England.

The validity of the model has been evaluated under Norwegian conditions, using data from multiharvest fertilization trials with irrigated cabbage crops, grown on soils with contrasting moisture-holding capacity. The assumption of critical %N was in good agreement with the development of dry matter production. Growth ceased prematurely in all cases where suboptimal N-concentrations were observed. Lower concentrations were always found on the sandy soil than on the loam. The model gave a good representation of the mineral-N reserves in both soils.