Nitrogen fertilisation of lettuce, processing tomato and sweet pepper: Yield, nitrogen uptake and the risk of nitrate leaching

Growth, nitrogen uptake and yield response were studied in two cultivars of lettuce (loose leaf type, LL, and butterhead type, BH) and processing toma to (early and late type) and in one cultivar of sweet pepper grown in the f ield at different levels of nitrogen fertiliser. In all the experiments, in creasing nitrogen supply increased crop growth, N uptake and yield but caus ed a linear decrease of the apparent recovery of the fertiliser nitrogen. I n lettuce maximum fresh weight yield was reached at a fertiliser-N rate of 158 kg ha(-1) in the LL type and 167 kg ha(-1) in the BH type. At these fer tiliser-N rates, the estimated N-uptake was 136 kg ha(-1) in LL and 121 kg ha(-1) in BH. Significant quantities of mineral nitrogen (i.e. 90 kg ha(-1) in LL and 101 kg ha(-1) in BH) were left by the crops in the soil at harve st. In processing tomato, both cultivars reached the highest yield at the 2 00 kg N ha(-1) rate with a N-uptake of 226 kg ha(-1) in the early cv and 25 9 kg ha(-1) in the late cv. At this N fertiliser rate, excess mineral nitro gen left by the crop in the soil at harvest ranged from 73 kg ha(-1) (late cv) to 89 kg ha(-1) (early cv). Moreover, N in crop residues amounted to ab out 100 kg ha(-1) in both cultivars. In sweet pepper, the maximum marketabl e yield was achieved with about 310 kg N ha(-1) with a N-uptake of 216 kg h a(-1). With that N fertiliser rate, excess soil mineral nitrogen at harvest was estimated at 223 kg ha(-1) and N in crop residues at 130 kg ha(-1). Th e different N uptake rates, apparent N recoveries and total N requirements of species and cultivars, together with the amount and fate of crop residue s, create different environmental risks (sweet pepper >> processing tomato congruent to lettuce).