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

Abstract

Core Ideas The main aim was to reduce N2O emission through crop residue removal or N immobilization through straw addition in fall. Annual N2O emission was reduced by 74% through removal of vegetable crop residues in fall. N2O emission in the removal treatment was as low as in the unfertilized control. Straw addition in autumn failed to reduce N2O emission (p = 0.057). 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.