N2O 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 N2O from soils. Despite numerous investigations on N2O fluxes, information on the impact of vegetable-production systems on N2O emissions in regions with winter frost is still rare. This present study aimed at measuring the annual N2O 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 N2O 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 N2O release from the treatments was 2.3, 5.7, 8.8, and 10.6 kg N2O-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 N2O 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 N2O 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.