Nitrogen mineralization from crop residues

Knowledge of the plant nutrient requirements in individual fields is necessary to determine the optimal fertilizer requirements of vegetables. The fertilizer effect of plant residues from the previous crop should therefore be taken into account when calculating fertilizer requirements. The N-requirements of leek were investigated on a sandy and a loamy soil, where the previous crops had been summer cabbage, Italian ryegrass (as a catch crop), and winter cabbage. Early and late leek were used to investigate the effect of the previous crop on yield, plant N-uptake, and levels of soil mineral-N for various levels of N-fertilizer. The nitrogen effect of the previous crop was greatest after winter cabbage, while Italian ryegrass and summer cabbage gave a considerable lower effect. On plots without N-fertilizer the average nitrogen taken up in the leek was 73 kg/ha after winter cabbage, 33 kg/ha after Italian ryegrass, and 17 kg/ha after summer cabbage. The fertilizer effect of previous crop was largest on late leeks. Yield and N-uptake on unfertilized plots were greater on loamy soil than on sandy soil. The average nitrogen taken up in the leek from fertilized plots was 104 kg/ha after winter cabbage, 95 kg/ha after Italian ryegrass, and 62 kg/ha after summer cabbage.