There are many studies proving the favourable effects of grass covers on the workings of the soil and on the polluting potential of the pesticides. They are described here, but uncertainties still remain. A synthesis of the studies in progress shows that grass covers (either in the crop rotation or as particular strips) first decreases the amounts of pesticides to be used per hectare, and moreover reduces the transfer of substances to places outside the farmed area by delaying the start of run-offs and by improving the infiltration and retention of the contaminating substances. The risk of pollution of the underground waters may also be diminished, according to the efficiency of the retention and bio-degradation processes, which occur mainly in the upper horizons. The questions regarding the fate of the stabilized residues, the evolution of the degradation processes, and the possible uptake of the pesticides by the grass vegetation are as yet but little studied.
