ALLEY CROPPING FOR MANAGING SOIL-EROSION OF HILLY LANDS IN THE PHILIPPINES

A field experiment was conducted on a hillslope to test three soil con servation-oriented alley cropping treatments, and to compare them with farmer's practice in terms of their effects on soil erosion and runof f. The alley cropping treatments had 1-m-wide, leguminous shrub hedger ows (Desmanthus virgatus) established along the contour, with an alley width of 5 m. Besides the effect of hedgerows, the effects of mulchin g and minimum tillage were also studied. The farmer's practice is char acterised by up-and-down slope tillage operations and weed-free cultur e. Maize and mungbean were used as wet and dry season crops, respectiv ely. Twelve erosion plots were laid out, with four treatments replicat ed three times. Each plot had a dimension of 6 m (across slope) by 12 m (downslope), and was equipped with electronic data loggers that meas ured rates of rainfall and runoff as a function of time. Total soil lo ss, divided into bed load and suspended load, was measured after each rainfall event. Due to high rainfall amount, lack of soil protection a nd steep slope, soil erosion rates in the farmer's practice were very large, reaching 100 to 200 t ha(-1) year(-1). However, these values we re markedly reduced to a rate of less than 5 t ha(-1) year(-1) in the alley cropping treatments, The reduction of soil loss in the alley cro pping was attributed to reduction in both total runoff volume and sedi ment concentration, A significant decrease in sediment concentration r esulted from higher contact cover that effectively protects the soil f rom both rainfall detachment and runoff entrainment, and the reduction in overland flow velocity associated with mulching with plant residue s and the presence of densely planted hedgerows. The reduction of tota l runoff was due to increased infiltration rates resulting from contou r ploughing, terrace formation and high infiltration rates in soil adj acent to hedgerows.