EFFECTS OF LEGUME LIVE-MULCH ON CROP PERFORMANCE, SOIL AVAILABLE NITROGEN AND CROP N STATUS IN INTENSIVE TROPICAL VEGETABLE PRODUCTION

In an attempt to introduce legume green manure to intensive tropical v egetable production, we studied the effects of live-mulch. Soil nitrog en, crop-N status, and yields were closely monitored in a continuous, year-round vegetable sequence from 1992 to 1995 in the rice-based lowl and environment of southern Taiwan. When live-mulch was newly establis hed at high density, vegetable yields were negatively affected. With c hange in proportion and spatial arrangement, inter-specific competitio n;was reduced. Besides direct competition between live-mulch and veget able intercrops, incorporating legume biomass into the soil resulted i n immobilization of available soil nitrogen. This effect was presumabl y conditioned by seasonal cool temperature. Short-term negative effect s of live-much on vegetable production were offset in the longer term by a positive influence of previous year's biomass of legume clippings on vegetable yields in 1994/95. No differences were found in minerali zed soil nitrogen between no-mulch and live-mulch treatments, but ther e was indication that crop-N status was better in live-mulch plots. Th is might have resulted from a slow but sustained mineralization of soi l organic nitrogen which was presumably improved by live-much applicat ion and was readily absorbed by vegetables. From a practical viewpoint , a live-mulch-vegetable system is probably too expensive and labour-i ntensive to implement for the minimal positive longer-term effects.