Potential of alternative crop rotations for reducing nitrate leaching losses in intensive vegetable rotations

Intensive field vegetable production is an important economic sector in Flanders. Several vegetable crops are harvested in a vegetative stage when high daily N uptake rates are achieved leaving behind soils with considerable N content. Vegetable crop residues take a particular position relative to arable crops due to often large amounts of biomass with a high N content left behind on the field. Vegetable crop residues have been found to mineralize rapidly even at low soil temperatures. These factors cause intensive vegetable rotations to be prone to nitrate leaching during winter. In order to obtain water quality objectives set by the nitrate directive three field experiments are set up to evaluate the potential of alternative crop rotations to reduce nitrate leaching during winter. The first alternative crop rotation examines the inclusion of Italian ryegrass (Lolium multiflorum) in cauliflower (Brassica oleracea var. botrytis) rotations. During the following spring the grass is harvested and a new cauliflower crop is planted. The second alternative crop rotation examines the use of two cover crops (Italian ryegrass or winter wheat (Secale cereale)) after a cauliflower crop. However in contrast to the first alternative rotation the cover crop will be incorporated during spring instead of harvested. Both alternative rotations are compared with a standard cauliflower – cauliflower rotation. The vegetable crop residues are treated in a conventional manner, namely being left on the field and incorporated. Results and findings of the first season will be presented at the symposium.