Response of common bean and groundnut to co-inoculation of trichoderma and rhizobia in an acid soil

Abstract

Common bean and groundnut are an important source of protein, fat, carbohydrates, vitamins and minerals for both humans and livestock. These legumes are produced mostly by smallholder farmers whose current yields are far below the potential yield of 2 t/ha for both legumes due to biological constraints, poor soil fertility and high soil acidity. Soil acidity poses the greatest challenge as it also affects availability of important nutrients such as phosphorus. This study investigated the sole and dual inoculation of Rhizobia and Trichoderma to common bean and groundnut in an acid soil. The soil in which these two crops were grown was characterized for: soil reaction, available phosphorus, total nitrogen, cations organic matter and soil respiration before planting and at harvest using standard laboratory procedures. Soils were amended with nitrogen (N) and phosphorus (P) fertilization at the rates of 100 kg N and 80 kg P2O5 per ha and seeds were dressed with; 1 g/kg of seed of Trichoderma harzianum; 100 g/kg of seed of Rhizobium tropici; or a combination of both inoculants at the recommended rates at planting. The experiment was set up in the greenhouse using the Completely Randomized Design (CRD) with the above amendments’ and a control without any amendment. The experiment consisted of two sets, one was nodulation and nodule effectiveness which were determined at 51 days after planting and the other was nitrogen and phosphorus accumulation in the above ground biomass, biomass and grain yield which were determined at maturity. To determine differences among soil amendments, data was analysed using Analysis of Variance and Least Significant Difference at 95 % confidence limit. Relationships among parameters were determined using correlation analysis. The results showed that amending soils with inorganic N at a rate of 100 kg N per hectare can depress nodulation even in the presences of high levels of inorganic P. Inoculating common bean and groundnut with the both Rhizobia and Trichoderma increased nodule activity. However, this increase did not translate to an increase in biomass or grain yield. The study also showed a low phosphorus accumulation in Trichoderma inoculated plants in both common bean and groundnut. Therefore, further investigations to study the extent of colonization and accompanying changes in root volume in common bean and groundnut inoculated with Trichoderma are recommended in order to understand the full effect of the Trichoderma.