Agricultural use of sewage sludge: impact on crop productivity and MTE transfer

Abstract

The Auvergne is an agricultural region with twenty six thousand square kilometres and one million five thousand hectares of useable farm area. There are two farming systems, which need organic products to manage the organic matter status of soils: - the crops in the plain of Limagnes - and the animal farming in the mountains region. In the context of the spreading refusal or the demand of departure for the law, the objectives of the project are to determine the impact of sludge spreading in real crop conditions on productivity and metallic trace element (MTE) contents. Our works confirm the interest of sludge use on agricultural soils in increasing the final dry matter production and playing on different stages of yield since of the first year of spreading. At this stage, they don't reveal direct risk of MTE plant contamination by the sludge spreading according to the regulation conditions. The variability of results relating to the impact of the sludge on the productivity and on the MTE soil/plant transfer from year to year and from site to site has led to constitute a data base of MTE with a threshold contents by species. In the future, the database must be extended to more annual crops. The final objective is to plan the cultural practices and particularly the organic matter management in respect of quality and environmental plant production.