EROSION AND CROP YIELD RESPONSE TO SOIL-CONDITIONS UNDER ALLEY CROPPING SYSTEMS IN THE PHILIPPINES

Conventional tillage (T1) and alley cropping treatments whether tilled-unmulched (T2), tilled-mulched (T3) or untilled-mulched (T4) were compared in terms of their effects on erosion, crop yield and selected properties of a clay soil on a 17% slope. The alley cropping systems consisted of 1 m wide contour hedges (three rows of Desmanthus virgatus planted at 10 cm spacing with 40 cm between rows) between 5 m wide alleys where maize (Zea mays L.) and mungbean (Phaseolus aureus) were grown sequentially. The hedgerows were pruned every 45-60 days to 50 cm height to provide green manure for the alley crops. After a 3 year trial, saturated hydraulic conductivity and air permeability during the pod development stage of the mungbean crop in T4 were at least twice that in T1 in both the 0-5 and 7-12 cm soil depths. In the 0-5 cm layer, soil bulk density was lower, and total porosity and the volume of pores with equivalent diameter > 30 mu m were significantly greater in T4 than in T1, whereas the opposite was true for the pore volume within the 10-30 mu m and < 0.2 mu m diameter ranges. The effect of T2 was superior to that of T1 but inferior to T3 or T4 in terms of erosion control, although comparable with the latter treatments with respect to mean crop yields. The mulched alley cropping systems T3 and T4 provided the lowest annual soil and nutrient losses and gave similar maize yields, but smaller mungbean yields, compared with the other treatments, and appear to be the most promising of the alley cropping systems tested.