No runoff, no soil loss : soil and water conservation in hedgerow barrier systems

Land degradation by water erosion represents a serious, and fast increasing, environmental threat. Hedgerow barriers control water erosion through the presence of the tree stem and through an increase in infiltration beneath the hedgerow. The infiltration rate beneath hedgerows is 3-8 times higher than in the alley where crops are grown. Soil water content measurements in hedgerow barrier systems indicate that infiltrated water penetrates the soil beneath hedgerows deeper than the soil beneath the alley and the control. An analytical framework for calculating the impact of hedgerows and mulch on infiltration, runoff and soil loss is presented here. The framework was expanded with algorithms to calculate the impact of hedgerows of various densities, ranging from 1-4 rows. The framework was applied on a seasonal basis and the predictions were satisfactory. Extreme events can be explained when dynamic soil and plant conditions are incorporated. A dynamic simulation model called SHIELD has been developed that explains the experimental observations for runoff, soil loss and crop yields using daily time steps. Application of the model illustrates the importance of dynamic soil and plant conditions to the amount of soil being lost and shows that SHIELD can be used to compute the maximum desired distance between hedgerows with respect to tolerable soil loss.