Growth and N accumulation in maize and winged bean as affected by N level and intercropping

Cereal-legume intercropping and other mixed cropping culture as practised traditionally in many Asian, African, and Latin American countries provide sustainable farming systems with enhanced land and energy use. Winged bean [Psophocarpus tetragonolobus (L.) DC.] is a readily nodulated tropical legume with high food value. Little is known concerning the intercropping potential of winged bean and maize (Zea mays L.) or the effects of nitrogen (N) levels on this intercrop system. In a greenhouse study with plants grown in containers widely spaced to minimize competition for light, dry matter accumulation and N concentration of both species were greater for plants grown with 7.5 mM NO₃^-(HN) than those grown with 0.75 mM NO₃^-(LN). The only effect of the cropping system on winged bean was a lower N concentration in intercrop than monocrop plants. Maize dry matter accumulation was reduced and tissue N concentration was increased with intercrop culture. These results indicated N stress did not cause the decreased growth of maize when grown with winged bean; an allelopathic effect of winged bean on maize may have occurred. The relative contribution of N₂ fixation (determined by ¹⁵N isotope dilution) to the total N accumulation of monocrop winged bean was significantly greater at LN than at HN. At 44 d after transplanting, the contribution of N₂ fixation to winged bean grown with maize was greater than when winged bean was grown alone. Winged bean nodule number was equivalent for all treatments. As N availability decreased due to intercrop culture and N level, concurrent increases were observed in nodule dry weight and the contribution of N₂ fixation to the N economy of winged bean.