Various studies have shown the beneficial effect of the presence of grasslands to reduce soil losses, whether in drained or non-drained situations.
A study by Chisci and Zanchi in 1981 1) (figure alongside) shows that soil losses are almost nil in the grassland. This study was conducted in the Piedmont region (Italy).
The analysis of the mechanisms leading to this beneficial effect was proposed by Ouvry et al. en 20102).
They show that this benefit is based upon two main factors:
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The first is the limitation of runoff. In fact, the presence of grasslands, on the one hand, slows down water slide thanks to presence of the herbaceous perennial aerial structure, and, on the other hand, encourages water filtration.
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The second mechanism is the important reduction of the quantity of mineral materials in suspension.
To quantify the benefit of the presence of herbaceous cover, Lecomte, in 1999 3), demonstrates that 10% of the surface of herbaceous cover downstream from an agricultural surface mallow reduces the runoff from 57 to 100%, and from 75 to 85% for materials in suspension.
To maximize this benefit, it is important for grassland or grass cover to be in good condition. It is thus advisable to avoid too high covers.
Understanding these mechanisms involves considering the position of the grassland, grass strips, and buffer zones on the scale of a landscape.
It is therefore necessary to promote the presence of buffer strips in the talwegs and maintain grasslands across these talwegs.