Adaptation des pratiques agricoles en fonction des exigences de la Directive Nitrates et validation des résultats via le suivi lysimétrique de la lixiviation de l'azote nitrique

Adaptation of agricultural practices according to requirements of the Nitrates Directive and validation through nitrates leaching follow up thanks to lysimeters. Since six years nitric nitrogen lixiviation is followed in six fields located in a silty area in Hesbaye (Belgium), mainly dedicated to vegetable crops. Open-field lysimeters are used, with the aim not to impede agricultural operations. These lysimeters allow the quantitative follow-up of the nitrate lixiviation below the root zone. The aims of the project are the setting up of better agricultural practices with regard to water quality on the one hand, and the adjustement of fertilization advice and the assessment of the impacts on yields, nitrogen remainder, and nitrate concentration in the water collected at the bottom of the lysimeter on the other hand. To reach these aims, experimental designs were set up in the parcels equiped with a lysimeter. These designs allow to test the impact of different levels of nitrogen fertilizers. An environmental indicator (APL in French) follow-up allows to make each year a report on the risk of nitrogen lixiviation related to the different objects tested on the subparcels. Finally, individual yields on the different subparcels are quantified to take the economic impact of the agricultural practices modification into account. During this test, the impact of a fertilization level reduction was just observed on the yields during double vegetable growing, only on the second crop. The other tests showed that a reduction of nitrogen fertilization level (in comparison with fertilization advice), and even, in some cases, no fertilization had no impact on yield and crop quality. A reflexion about soil sampling date for nitrogen fertilization advice was also lead