Effect of Crop Residue Removal and Straw Addition on Nitrous Oxide Emissions from a Horticulturally Used Soil in South Germany

Vegetable production, such as cauliflower (Brassica oleracea var. botrytis L.) or broccoli (Brassica oleracea var. italica P.), is often associated with high N surpluses, posing the risk for substantial N losses. Straw addition in autumn to immobilize surplus N over winter or removal of vegetable crop residues were shown to reduce nitrate leaching efficiently. However, the effect of these management measures on the release of nitrous oxide (N₂O) is still unclear. We determined N₂O fluxes from a vegetable field with a silty texture in southern Germany over 2 yr in the following treatments: no N fertilization (−N), conventional N fertilization without (CON), and N fertilization with crop residue removal (−CR) or straw addition (+S). Marketable fresh matter yields and N uptake showed only minor differences among all N-fertilized treatments. Enhanced N₂O fluxes occurred over a period of nearly 6 mo in the first year in autumn and winter after crop residue incorporation. Positive correlations between N₂O fluxes and driving soil variables suggested denitrification as the major N₂O source. Cumulative N₂O emission ranged between 5.2 (−CR) and 37.2 kg N₂O–N ha⁻¹ yr⁻¹ (CON). Crop residue removal reduced N₂O emission in CON very efficiently by 74%. Straw addition reduced N₂O emission in only 1 yr. The N₂O emission factors were 4.3, 1.9, and 3.1 for CON, −CR, and +S, respectively. The high N₂O reduction by crop residue removal seems to be promising in terms of mitigation, but long-term effects, such as missing humus reproduction, should be considered in future studies.