Tomato Crop Response to Short‐Duration Legume Green Manures in Tropical Vegetable Systems

The potential of legume green manure (GM) as an alternative to mineral N fertilizer in tropical horticulture has received scant attention. The feasibility of meeting N needs of tomato ( Lycopersicon esculentum Mill.) with GM was studied in six field experiments at three locations in major vegetable growing areas of Taiwan and the Philippines between 1993 and 1995. Legume biomass, N 2 fixation and N accumulation, and tomato yield and N uptake were quantified within a 6‐mo experiment cropping pattern. Yields of GM‐amended tomato crops were compared with those amended with fertilizer N (0–150 kg N ha −1 ). The residual effect of the fertilizing method of a second crop (maize; Zea mays L.) was estimated at AVRDC by measures of biomass and N uptake 30 d after sowing. Legume N recovery in tomato crops was traced with 15 N at Mariano Marcos State University (MMSU). Soybean [ Glycine max (L.) Merr.] harvested at 60 to 74 d accumulated a minimum of 2.8 Mg ha −1 biomass and 100 kg ha −1 N in all locations and seasons. A maximum of 6 Mg biomass ha −1 and 140 kg N ha −1 was reached in the wet season (WS) at AVRDC. Indigofera ( Indigofera tinctoria L.) and mungbean [ Vigna radiata (L.) Wilcz.] biomass yields were more variable and always inferior than soybean yields. Tomato yields across locations ranged from 3 to 70 Mg fruit ha −1 . Tomato yields responded to GM N in the WS in Taiwan and in the northern Philippines, comparing favorably with fertilizer at 38 to 120 kg N ha −1 . No response to GM N was found in the dry season (DS) at AVRDC or at Bukidnon Resources Company, Inc. (BRCI). The 15 N experiments showed that only a small fraction of legume N (9–15%) was recovered by the tomato crop at MMSU. Maize biomass and N uptake, following the tomato crop, was increased with soybean GM compared with the control in the AVRDC WS and DS. Tomato yield response to GM N is high on infertile soils and tomato N requirement can be substituted fully or partially by GM, depending on soil N mineralization.