Nodulation, Nutrient Uptake and Yield of Common Bean Inoculated with Rhizobia and Trichoderma in an Acid Soil

Common bean is an important source of protein, fat, carbohydrate, vitamins and minerals for both human beings and livestock. In Zambia, common bean is produced mostly by smallholder farmers whose current yields fall far short of the potential 2 t/ha due to various challenges. Among the biophysical constraints, poor soil fertility and acidity pose the greatest challenges. This study investigated the individual and dual inoculation of Rhizobia and Trichoderma to common bean in a phosphorus deficient, acid soil. Soil in which the common bean was grown was characterized for selected chemical properties before planting and at harvest using standard laboratory procedures. Soils were amended with nitrogen and phosphorus fertilizer at the rates of 100 kg N and 80 kg P2O5 per ha; 1 g/kg of seed of Trichoderma harzianum; 100 g/kg of seed of Rhizobium tropici; or a combination of both at the recommended rates at planting. Nodulation and nodule effectiveness were determined at 51 days after planting. Nitrogen and phosphorus accumulation in the above ground biomass, biomass and grain yields were determined at maturity. To determine differences among soil amendments, data were 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 high rates can depress nodulation even in the presence of high levels of inorganic phosphorus. Inoculating common bean with Rhizobia and Trichoderma either singly or in combination increases nodule number and effectiveness per plant but may not result in higher nitrogen and phosphorus accumulation, or in an increase in subsequent biomass or grain yields. The low phosphorus accumulation in Trichoderma inoculated plants observed in this study needs to be investigated further by studying the extent of colonization and the accompanying changes in root volume.