Effects of cereal roots on detachment rates of single- and double-drilled topsoils during concentrated flow

Farmers in Europe want to control soil erosion in ways that are easily incorporated in their normal practices. We have investigated the possibility of reducing soil erosion by concentrated flow (i.e. rill and gully erosion) through increasing the root density of cereal crops. In situ root density measurements on cereal fields were combined with laboratory flume experiments on samples, taken in single- and double-drilled fields, of which the above-ground biomass was clipped. During the laboratory experiments no significant effect of root densities on critical shear stress or channel erodibility was observed because of interactions with other changing parameters (e.g. ageing effects). Therefore, the expected relative detachment rates as a function of plant root density were calculated using an empirical equation. During the first 75 days of the crop growth season relative soil detachment rates for single-drilled field parcels can be reduced up to 50% compared with a rootless field, whereas relative soil detachment rates in double-drilled field parcels can be reduced up to 60% in this period. Thereafter, plant roots in double-drilled field parcels reduce relative soil detachment rates on average by 9% compared with single-drilled field parcels (up to an absolute maximum of 90% compared with rootless soils). During the growing season, not only root density increases but also the vegetation cover changes, which enhances soil protection from erosion. Therefore, cereal roots will help to conserve the soil when seed is drilled at double rates, especially during the early growth stages and in fields with medium risk of concentrated flow.