Biotechnologie, Agronomie, Société et Environnement (Jan 2010)
Suivi de la percolation du nitrate en terres cultivées par la technique lysimétrique
Abstract
Monitoring of nitrate leaching in croplands by lysimeters. The European Nitrates Directive (91/676/CEE) aims at moderating or preventing water pollution with nitrates issued from agricultural practices. The Walloon region transposed it into its law and initiated a Sustainable Nitrogen Management Program on 2002, also called PGDA in French. Six lysimeters have been implemented in agricultural open fields, being under real condition of industrial harvest crops, especially vegetable ones. The lysimeters are used as follow up tools to monitor and quantify the amount of nitrates leaching beyond root zone towards underground water ressource. This study demonstrates that lysimeters are efficient and permit to collect representative quantity of seepage water. Their nitrates content, combined with data related to agricultural practices, fertilisation rates and advised, climate, the defined environmental indicator (APL) provide a global approach to link agricultural practices and underground water protection from nitrates pollution. The lysimeters validate the reliability of the environmental indicator (APL) with the nitrates content in leaching water, which will not be catched up by the next crop. Unfortunately, it is also demonstrated that even when the nitrogen management is respectful of the related legislation, the warranty to respect the targeted norms of water quality on nitrates is not ensured. The lysimeter tool clearly shows that the respect of seepage water quality standards issued from industrial agriculture does not have to be considered crop per crop but rather from an integrated and global approach of the complete crop sequences and rotations, in respect with best agricultural practices, reasonable fertilisation rates, inset crops, etc. for each individual crops. Some favourable and non favourable crop sequences to nitrates content of underground water are listed. Experiments are in progress on crop sequences evaluation and fertilisation levels and advises for Walloon industrial crops and their impacts on the leaching water quality and nitrates content collected by lysimeters.
