N 2 O fluxes from a Haplic Luvisol under intensive production of lettuce and cauliflower as affected by different N‐fertilization strategies

Vegetable‐production systems often show high soil mineral‐N contents and, thus, are potential sources for the release of the climate‐relevant trace gas N 2 O from soils. Despite numerous investigations on N 2 O fluxes, information on the impact of vegetable‐production systems on N 2 O emissions in regions with winter frost is still rare. This present study aimed at measuring the annual N 2 O emissions and the total yield of a lettuce–cauliflower rotation at different fertilization rates on a Haplic Luvisol in a region exposed to winter frost (S Germany). We measured N 2 O emissions from plots fertilized with 0, 319, 401, and 528 kg N ha –1 (where the latter three amounts represented a strongly reduced N‐fertilization strategy, a target value system [TVS] in Germany, and the N amount fertilized under good agricultural practices). The N 2 O release from the treatments was 2.3, 5.7, 8.8, and 10.6 kg N 2 O‐N ha –1 y –1 , respectively. The corresponding emission factors calculated on the basis of the total N input ranged between 1.3% and 1.6%. Winter emission accounted for 45% of the annual emissions, and a major part occurred after the incorporation of cauliflower residues. The annual N 2 O emission was positively correlated with the nitrate content of the top soil (0–25 cm) and with the N surpluses of the N balance. Reducing the amount of N fertilizer applied significantly reduced N 2 O fluxes. Since there was no significant effect on yields if fertilization was reduced from 528 kg N ha –1 according to “good agricultural practice” to 401 kg N ha –1 determined by the TVS, we recommend this optimized fertilization strategy.