The French programme of drainage reference areas. Methodology and first results

Abstract

The French Programme of Drainage Reference Areas, launched in 1980 by ONIC and the Ministry of Agriculture together with the scientific and technical assistance of both INRA (Montpellier) and CEMAGREF (Antony and Bordeaux), is aiming at developing drainage in French farms. As drainage involves high investments, farmers have to be provided with all the technological, agronomic and economic information required to improve waterlogged lands. The programme is threefold. Firstly, soil surveys are carried out for a small area (500 to 1 500 ha) in order to determine the best drainage method. Secondly, main collectors and open channels are made. Thirdly, conditions under which farms of this area can get the best results from drainage are studied. These studies require a good knowledge of farm management. On the one hand, the financial and technical conditions of the drawbacks due to excess water content. On the other hand, the lines along which research and extension must be implemented should be established to get the best returns from drainage. The first results from this programme mainly show which types of farm management require drainage. They are illustrated by two examples: the “Pays de Bray” in the French department of Seine Maritime (North Western France) and the “Lower Briande Valley” in the department of Vienne (Mid Western France). The “Pays de Bray” is a grassland region with dairy or mixed farms; more than forty per cent of the farm land is waterlogged and often flooded. The region includes three farm types which manage excess water in various ways; only one farm type is interested in drainage. The “Lower Briande Valley” produces mainly cereals and oilseed crops on more than two thirds of its area. Eighty per cent of the soils should be drained. Three farm types were identified; one is draining most of its soils while another farm type is planning drainage for the wettest soils only. Both examples from two different regions show that, whatever the constraints due to excess water, drainage investment can only be planned for some farm types characterized by their history, current crop production system and prospects. Drainage sometimes appears to be essential for developing or stabilizing a crop production system which is now too dependent on weather conditions.