Short-term Evaluation of Some Indigenous Legumes as Green Manures or Components of Rice-based Relay Intercropping Systems and Their Effect on Residual Soil Properties in the Rainforest Zone of Nigeria

Aim: To evaluate the potentials of some legumes as in situ green manures or components of relay intercropping with direct-seeded upland rice, and to assess the effect of incorporating their biomass into the soil on residual soil properties.

Study Design: The treatments were laid out in randomised complete block design, replicated three times.

Methodology: Some indigenous legumes were used as green manures or as components of upland rice-based cropping systems to assess their effect on the performance of rice and on residual soil properties in the rainforest region of Nigeria. Mucuna pruriens, Vigna sinensis, Vigna subterranea, Vigna unguiculata ; (var Ife BPC and Ife Brown), Sphenostylis stenocarpa were either incorporated in situ into the soil as green manure at 8weeks after sowing or relay-intercropped with NERICA 2 rice giving a total of 16 treatments.

Results: Significantly higher number of panicles/plant, grain and straw yield were obtained with sole, than with green manuring and relay cropping in the first cropping season, but in the second season, cowpea and mucuna bean green manures gave the same outcomes. The residual soil N accumulated during a two consecutive-year green manuring programme with either cowpea or mucuna bean was sufficient to produce a rice yield equivalent to the split application of 60 kg N/ha. Intercropping reduced rice grain yield by between 5.4 and 47.0 %, with cowpea (Ife brown)/Rice system performing best.

Conclusion: In the short-term, leguminous crop species especially those with determinate growth habit and lower carbon to nitrogen ratio can be integrated into upland rice-based cropping systems in the rainforest region of Nigeria as intercrops, but preferably as green manure crops.