Landscape benching from tillage erosion between grass hedges

Grass hedges are narrow (1-2 m wide) parallel strips of stiff, erect, grass planted near to or on the contour of fields but crossing swale areas at an gles convenient for farming. They serve as guides for contour cultivation, retard and disperse surface runoff, cause deposition of eroded sediment, an d reduce ephemeral gully development. After three years of tilled fallow be tween mixed-species hedges, the average grade of 18, m wide tilled strips b etween 1.5 m wide hedges was reduced from 0.068 to 0.052 as a result of sur face lowering below hedges and on the shoulders of swale areas combined wit h increases in elevation above hedges. Annual surveys show progressive lowe ring of high spots and filling of low spots as contours lines more closely aligned with hedges. Survey data indicated annual erosion rates of nearly 2 50 t ha(-1) year(-1). Both RUSLE and WEPP over-predicted erosion rates, par tly because backwater and slope modification affects were not considered. A tillage translocation model predicted enough soil movement to account for 30-60% of the observed changes. A combination of tillage translocation and water erosion/deposition provides the best explanation for the observed agg radation/degradation patterns. (C) 1999 Elsevier Science B.V.