Hedgerows and mulch as soil conservation measures evaluated under field simulated rainfall

Hedgerows and residue cover have been reported as successful practices to reduce soil and water losses on steep lands. However, there is a lack of information on the efficiency of hedgerow types, hedgerow-mulch interaction and the effect of soil moisture and slope (gradient and length) on the overall performance of these practices. Results from four experiments using Vetiver and other grasses under simulated field conditions in Venezuela are presented. The experiments were conducted in the mountain coastal range of Venezuela, at 1800 m above sea level, where intensive horticultural systems occupy steep lands. A double nozzle rainfall simulator, yielding an average intensity of 55.6 mm h⁻¹ was used on 5 m length and 0.5 m wide plots, on an Aquic Paleudult soil with different soil moisture conditions and two 15% and 26% slopes, in order to evaluate the efficiency of five 50 cm wide hedgerows: Vetiver (Vetiveria zizanioides), Lily (Agapanthus africanus), Fern (Nephrolepis sp.), Lemon grass (Andropogon citratum) and no hedgerow; and five levels of pine needles residues: 0, 0.5, 1.5, 3 and 5 Mg ha⁻¹. Upland flow was simulated using a flow equal to an 80% rainstorm runoff as obtained under wet and very wet conditions, in order to imitate equivalent slope lengths. Hedgerows and mulch were good conservation measures, especially when they were combined. Vetiver grass and Fern were the more efficient hedgerows because of their highly dense vegetative structure. Residue requirements are less when the slope is protected by hedgerows. Larger intervals between hedgerows would be possible provided there is mulch between hedgerows. A table is presented as a guideline to design hedgerows spacing considering rainfall erosivity, soil erodibility and crop-management intensity.