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 vegetable production, we studied the effects of live-mulch. Soil nitrogen, crop-N status, and yields were closely monitored in a continuous, year-round vegetable sequence from 1992 to 1995 in the rice based lowland environment of southern Taiwan. When live-mulch was newly established at high density, vegetable yields were negatively affected. With change in proportion and spatial arrangement, inter-specific competition was reduced. Besides direct competition between live-mulch and vegetable intercrops, incorporating legume biomass into the soil resulted in immobilization of available soil nitrogen. This effect was presumably conditioned by seasonal cool temperature. Short-term negative effects of live-mulch on vegetableproduction 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 mineralized soil nitrogen between no-mulch and live-mulch treatments, but there was indication that crop-N status was better in live-mulch plots. This might have resulted from a slow but sustained mineralization of soil organic nitrogen which was presumably improved by live mulch application and was readily absorbed by vegetables. From a practical viewpoint, a live-mulch-vegetable system is probably too expensive and labour-intensive to implement for the minimal positive longer-term effects.