Farmer participatory research to minimize soil erosion on steepland vegetable systems in the Philippines

Soil erosion coupled with productivity decline: is considered a major const raint to sustainable vegetable production in Southeast Asian steeplands, ye t soil conservation technologies acceptable to vegetable growers have not b een developed. Effectiveness of high-value contour hedgerows species [(Aspa ragus (Asparagus officinalis L.), pineapple (Ananas comosus (L.) Merr.), pi geon peas (Cajanus cajan (L,) Millsp.), lemon grass (Cymbopogon flexuosus ( Nees ex Steud.) Wats.), and tea (Camellia sinensis (L.) O. Kuntze)] on cont rol of steepland erosion was evaluated in a replicated researcher-managed f ield experiment, and 12 farmer-managed erosion-runoff plots from 1995 to 19 98 across the landscape of the Manupali watershed in Mindanao, the Philippi nes. Annual soil loss from 42% slopes with superimposed researcher-managed high-value contour hedgerows treatment (45.4 Mg ha(-1)) was lower by 30% co mpared to the conventional practice of up-and-down cultivation (65.3 Mg ha( -1)). Annual soil loss measured in farmers' plots ranged from 1.4 Mg ha(-1) to 52.5 Mg ha(-1) on slopes ranging from 16 to 65%. Soil pH, organic C, to tal-N, and P downslope were greater by 7, 28, 13, and 10%, respectively, co mpared to upslope. Total-N, organic C, soil pH, Mg, and K measured at the e nd of the experiment in the researcher-managed contour hedgerows plots were lower by 35, 20, 30, 53, and 70%, respectively, compared to initial values . The Erosion-Productivity Impact Calculator (EPIC) model was used to asses s the effects of annual cropping sequences under a contour hedgerow system on slopes ranging from 15 to 65%. The cabbage (Brassica oleracea var. capit ata L.)-tomato (Lycopersicon esculentum Mill.)-cabbage sequence (the first crop planted in January) resulted in an average simulated annual soil loss of 28.1 Mg ha(-1) across slope ranging from 15 to 65%, whereas tomato-cabba ge-tomato resulted in an annual simulated soil loss of 98.3 Mg ha(-1). The cropping sequence of tomato-cabbage-tomato lost 3.0 Mg ha(-1) more soil at 15% slope than did the cabbage-tomato-cabbage sequence, while at 65% slope, the tomato-cabbage-tomato sequence lost 181.2 Mg ha(-1) more than the othe r sequence. On average, two-thirds of the total soil loss occurred during S eptember-December. In order to reduce soil loss acid increase productivity in steep sloping lands, high-value contour hedgerows with sequential croppi ng sequences that include either corn (Zea mays L.) or cabbage rather than tomato during the most erosive period of the year and variable fertility ma nagement strategies along the slope positions are suggested. The coincidenc e of predicted to actual soil loss from farmer-managed plots, based largely upon model development from researcher-managed plots, and the acute awaren ess instilled amongst farmer cooperators of the magnitude of soil loss, str engthen the argument for farmer participatory research. (C) 2000 Elsevier S cience B.V. All rights reserved.