Indian Journal of Agronomy

An on-farm field experiment was conducted in 24 farmers’ fields in randomized block design with 5 treatments. Introduction of vegetables, viz. ‘Vellayani Jyothika’, yardlong bean (Vigna unguiculata L. ssp. sesquipedalis), ‘Arka Anamika’ okra (Abelmoschus esculentus L.), ‘Saubhagya’ oriental pickling melon (Cucumis melo L. var. conomon) and ‘Arun’ amaranth (Amaranthus tricolor L.) in summer fallow of traditional double crop ‘Uma’ rice (Oryza sativa L.) in a humid tropical irrigated lowland was attempted during 2009–13 at Pathanamthitta, Alapuzha and Kottayam districts of Kerala. System yield, soil-nutrient balance and economics of the systems were compared. Rice-rice-yardlong bean system could realize higher productivity and profitability. Recycling of yardlong bean residues back into system could add to actual N and K gain and overcome actual P loss observed in soil. Rice-grain-equivalent yield of rice-rice-yardlong bean was the highest (35.39 t/ha), followed by rice-rice-amaranth (28.65 t/ha). The lowest rice-grain-equivalent yield was recorded from rice-rice-fallow (10.63 t/ha). Rice-rice-yardlong bean had better sustainable-yield index (0.62), system productivity (96.96 kg/ha/day), land-use efficiency (91.79%), apparent nutrient-use productivity (118 kg/kg N, 221 kg/kg P₂O₅ and 177 kg/kg K₂O), net returns ( 252 × 10³/ha), sustainable-value index (0.40), system profitability ( 751/ha/day) and net returns per rupee invested (1.95) than the other systems. Soil-nutrient balance under rice-rice-yardlong bean showed gain of 39 and 47 kg/ha of N and K respectively.