Christine Le Bas

Main Lessons Drawn from the Analysis of the Literature

Planting and destruction are the two main phases in cover crop management techniques. Their dates and implementation conditions play a key role in terms of the various functions targeted for these crops (nitrate-trapping, erosion prevention, weed control, effect on next crop, etc.). The analysis of the literature therefore focused on cover crop planting and destruction techniques. The aim was to identify the different methods and, if possible, their effectiveness with respect to the success of sowing and destruction. The issue of the implementation of these techniques by farmers was then examined by analysing the constraints in terms of organization of labour and implementation costs.

Study Context and Methodology

In crop rotation, the fallow period is the period between the harvest of the main crop (sown for the purpose of harvesting) and the sowing of the next (Fig. 1.1). Depending on the harvesting and sowing dates of main crops, it can last from several days in the case of late harvest followed by sowing of a winter crop, to several months (up to 9 months) in the case of a spring crop. During this period, soil that is left “bare” (without plants), especially in the event of a long fallow period, can significantly increase the risk of leaching of nitrate into aquifers. The use of a cover crop as a nitrate-trapping “catch crop” can reduce this phenomenon of nitrate transfer in variable proportions depending on the soil and climate conditions, as well as the cropping system. The reduction lies in the range of 20–90 % compared to bare soil. This broad range of efficacy needs to be analysed on the basis of factors determining water drainage and nitrate leaching, as well as the other multiple functions of cover crops.