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 vegetable systems. Little information is available on the effectiveness of soil conservation measures under sloping intensified vegetable systems on volcanic ash-derived soils. We hypothesized that contouring, strip cropping, and high-value contour hedgerows--asparagus (Asparagus officinalis L.), pineapple [Ananas comosus (L.) Merr.], pigeonpea [Cajanus cajan (L.) Huth], and lemongrass [Cymbopogon flexuosus (Nees ex Steudel) J.F. Watson]--reduce soil loss compared with the farmer's traditional practice of up-and-down cultivation on sloping lands. A field experiment tested these soil conservation technologies from 1995 to 1998 in a completely randomized block design on a 42% natural slope on a clayey, halloysitic, isothermic, Typic Kandiudox. The greatest annual soil loss (65.3 t ha(-1)) was in the up-and-down system 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. Three 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% for tomato (Lycopersicon esculentum Miller), 36% for corn (Zea mays L.), and 78% for cabbage (Brassica oleracea var. capitata L.) than for upslope. In the contour hedgerow treatment, rapid terrace development changed soil properties, and crop yields for the bottom portions of bioterraces were greater by 121% for corn and 50% for tomato than yields of top portions.