Emissions of nitrous oxide and ammonia after cauliflower harvest are influenced by soil type and crop residue management

The decomposition of vegetable crop residues, e.g. from Brassica species, can cause substantial nitrous oxide (N2O) and ammonia (NH3) emissions due to their high nutrient and water contents. One promising approach to reduce these harmful emissions is optimizing post-harvest crop residue management. So far published results on the effects of different crop residue placement techniques on N2O and NH3 emissions do not give a consistent picture. One of the key issues is the diverse experimental conditions, in particular with respect to soil characteristics. Therefore, we studied the effects of cauliflower residue management, i.e. no residues (control), surface application (mulch), incorporation by mixing (mix), incorporation by ploughing (plough), on N2O and NH3 emissions in a 7.5-months field study, using a unique open-air facility featuring three different soils with contrasting soil texture (loamy sand, silt loam, sandy clay loam). Cauliflower residues caused the highest N2O emissions after ploughing (2.3–3.4 kg N2O–N/ha, 1.5–2.2 % of residue-N), irrespective of the soil type. In contrast, ammonia emissions were only affected by the residue placement technique in loamy sand, which exhibited the highest emissions in the mulch treatment (1.9 kg NH3–N/ha, 1.2 % of residue-N). In conclusion, under the given conditions incorporating crop residues by ploughing appears to produce the highest N2O emissions in a range of soils, whereas surface application may primarily increase NH3 emissions in coarse-textured soils.