In situ management of vegetable crops residues for reducing nitrate leaching losses in intensive vegetable rotations

Vegetable crop residues constitute an important link in the soil nutrient and organic carbon cycle and aid in maintaining soil quality and fertility. However during autumn large amounts of N are released by vegetable crop residues causing important N-losses through leaching. Crop residues thus pose a possible threat to meeting water quality objectives, while at the same time being a vital link in closing the nutrient and organic matter cycle of soils. A set of field experiments was set up to evaluate following on-field crop residue management strategies: (i) conventional incorporation of crop residues, (ii) leaving the crop residues untouched on the field and (iii) total removal of crop residues. The field experiments were performed with crop residues of cauliflower (Brassica oleracea var. botrytis), leek (Allium porrum) and headed cabbage (Brassica oleracea convar. capitata var. Alba). Soil samples were taken monthly in three layers: 0-30 cm, 30-60 cm, 60-90 cm. Crop residue biomass and N-content were determined before the winter period to assess N-uptake and after winter period to asses N-loss due to decomposition. Total soil mineral N content was generally higher following incorporation of vegetable crop residues compared to leaving them untouched on the field or to total removal. Crop residues left untouched appeared to continue taking up N from the soil, thus further depleting the soil mineral N. More results will be presented at the symposium.