Erosion and productivity of vegetable systems on sloping volcanic ash-derived Philippine soils

Soil erosion is a major constraint to the sustainability of sloping-land ve getable systems. Little information is available on the effectiveness of so il conservation measures under sloping intensified vegetable systems on vol canic ash-derived soils. We hypothesized that contouring, strip cropping, a nd high-value contour hedgerows - asparagus (Asparagus officinalis L.), pin eapple [Ananas comosus (L.) Merr.], pigeonpea [Cajanus cajan (L,) Huth], an d lemongrass [Cymbopogon flexuosus (Nees ex Steudel) J. F. Watson] - reduce soil loss compared with the farmer's traditional practice of up-and-down c ultivation on sloping lands. A field experiment tested these soil conservat ion technologies from 1995 to 1998 in a completely randomized block design on a 42% natural slope on a clayey, halloysitic, isothermic, Typic Kandiudo x, The greatest annual soil loss (65.3 t ha(-1)) was in the up-and-down sys tem and comparative values were 37.8 t ha(-1) for contouring, 43.7 t ha(-1) for strip cropping, and 45.4 t ha(-1) for high-value contour hedgerows. Th ree rain events alone caused 47% of the total soil loss. All erosion-runoff plots showed large differences in soil properties and crop yields between the upper and the lower slope. Crop yields downslope were greater by 40% fo r tomato (Lycopersicon esculentum Miller), 36% for corn (Zea mays L.), and 78% for cabbage (Brassica oleracea var, capitata L.) than for upslope. In t he contour hedgerow treatment, rapid terrace development changed soil prope rties, and crop yields for the bottom portions of bioterraces were greater by 121% for corn and 50% for tomato than yields of top portions.