Alley cropping for managing soil erosion of hilly lands in the Philippines

A field experiment was conducted on a hillslope to test three soil conservation-oriented alley cropping treatments, and to compare them with farmer's practice in terms of their effects on soil erosion and runoff. The alley cropping treatments had 1-m-wide, leguminous shrub hedgerows (Desmanthus virgatus) established along the contour, with an alley width of 5 m. Besides the effect of hedgerows, the effects of mulching and minimum tillage were also studied. The farmer's practice is characterised by up-and-down slope tillage operations and weed-free culture. Maize and mungbean were used as wet and dry season crops, respectively. Twelve erosion plots were laid out, with four treatments replicated three times. Each plot had a dimension of 6 m (across slope) by 12 m (downslope), and was equipped with electronic data loggers that measured rates of rainfall and runoff as a function of time. Total soil loss, divided into bed load and suspended load, was measured after each rainfall event. Due to high rainfall amount, lack of soil protection and 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 were 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 cropping was attributed to reduction in both total runoff volume and sediment concentration, A significant decrease in sediment concentration resulted from higher contact cover that effectively protects the soil from both rainfall detachment and runoff entrainment, and the reduction in overland flow velocity associated with mulching with plant residues and the presence of densely planted hedgerows. The reduction of total runoff was due to increased infiltration rates resulting from contour ploughing, terrace formation and high infiltration rates in soil adjacent to hedgerows.