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 com pared in terms of their effects on erosion, crop yield and selected pr operties of a clay soil on a 17% slope. The alley cropping systems con sisted of 1 m wide contour hedges (three rows of Desmanthus virgatus p lanted at 10 cm spacing with 40 cm between rows) between 5 m wide alle ys where maize (Zea mays L.) and mungbean (Phaseolus aureus) were grow n sequentially. The hedgerows were pruned every 45-60 days to 50 cm he ight 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, s oil bulk density was lower, and total porosity and the volume of pores with equivalent diameter > 30 mu m were significantly greater in T4 t han in T1, whereas the opposite was true for the pore volume within th e 10-30 mu m and < 0.2 mu m diameter ranges. The effect of T2 was supe rior to that of T1 but inferior to T3 or T4 in terms of erosion contro l, although comparable with the latter treatments with respect to mean crop yields. The mulched alley cropping systems T3 and T4 provided th e 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.