Evaluation of soil fertility benefits of hairy vetch (Vicia Villosa Roth) in smallholder maize based cropping systems of Central Zimbabwe

Abstract

There is soil fertility decline in maize (Zea mays L.)-based smallholder farming areas as a result of insufficient or lack of application of soil ameliorants. While some options can be employed such as manuring, cover cropping, intercropping and planting leguminous trees, these are often limited in terms of adaptability to very poor infertile soils and ability to give high returns on investment to encourage farmer adoption. This study sought to evaluate the potential soil fertility and maize yield benefits of hairy vetch (Vicia villosa L.) when used in rotation or intercropped with maize. Field experiments on maize-legume rotations and relay intercropping were conducted from the 2009/2010 to 2011/2012 cropping seasons in Wedza and Chihota communal areas, and on-station at the Grasslands Research Station in Marondera. Greenhouse and field experiments were also setup during the 2011/2012 season to evaluate the effect of soil acidity and Rhizobium leguminosarum strain on growth and N2 fixation of hairy vetch. Results from the maizelegume rotation experiment showed that when legumes were basal fertilized with 300 kg ha -1 NPK fertilizer (7N : 14 P2O5 : 7 K2O), sunnhemp produced the highest aboveground biomass (7.7 t ha -1) followed by cowpea (5.9 t ha -1) and hairy vetch (2.5 t ha -1) during the first season (2009/2010). Sunnhemp also fixed more N2 (161.5 kg N ha -1) than cowpea (84.7 kg N ha -1) and hairy vetch (25 kg N ha -1). There were no significant differences (P > 0.05) in maize grain yield between basal fertilized maize that followed basal fertilised legumes and maize that was fertilised with ammonium nitrate (34.5% N) and NPK fertiliser. When relay intercropped and provided with 300 kg ha -1 NPK, sunnhemp was also superior in improving maize grain yields by at least 50% compared to the control. Leaching tube incubations revealed that residues of hairy vetch, cowpea and sunnhemp mineralized about 18% more N than when they were mixed with maize residues. They were however, no significant differences in net N mineralized between the sole legumes residues for the 56 day incubation period. The liming and inoculation experiment revealed that there were no significant differences in biomass production of hairy vetch between limed and unlimed (acidic) soil, implying that soil acidity (pH 4.7) was not a significant problem to hairy vetch. The R. leguminosarum strain had a significant effect on biomass production and when hairy vetch was inoculated with the strain MAR833 it fixed up to 66.5 kg N ha -1. Inoculating hairy vetch with the strain MAR833 improved its biomass production to 3.1 t ha -1 compared to the control (0.37 t ha -1). In low soil fertility conditions coupled with erratic rainfall distribution it might be worthwhile to include sunnhemp in maize cropping systems as compared to cowpea and hairy vetch. However the potential of hairy vetch still needs to be assessed with new inoculant strains and more multi-location experiments should be done to identify a strain that can further boost its biomass production.