Nodulation of beans with inoculant carriers from pyrolyzed and non-pyrolyzed sugarcane bagasse in response to different pre-planting water availability

Abstract

Over the past few decades elite strains of rhizobia have become commercially available for agricultural production. However, these elite rhizobia are often not as competitive as native strains under adverse edaphic conditions, primarily concerning tolerance to soil desiccation. Biochar has been proposed as a soil amendment to reduce water stress. The effect of biochar made from sugar cane bagasse on rhizobium survival and inoculation of beans was tested in comparison to uncharred sugarcane bagasse and an unamended control in the greenhouse using a gradient of soil-sand mixtures (0%, 25%, 50%, 75%, 100% sand in the mixture) under two watering regimes over eight weeks between inoculant addition and planting in comparison to a control where inoculants were applied at planting. For the control, shoot growth did not differ between the charred or uncharred carrier materials (P > 0.05). However, the number of nodules was ten- and 13-fold greater with uncharred bagasse over biochar or control carriers, respectively. When pots were allowed to dry for eight weeks between inoculant addition and planting, the bagasse carrier was the only carrier that resulted in root nodules. With intermittent between inoculant application and planting, shoot biomass with the biochar carrier was 147 and 151% greater than with the bagasse and control carriers, respectively. Under the same intermittent drying, nodule number using the bagasse carrier was 925% greater than that with the biochar carrier, while nodules were absent in the control. DNA fingerprinting of the root nodules indicated that nodule occupancy was dominated by native rhizobia and not the introduced strain. However, occupancy of the introduced CIAT899 in bean nodules (1–38%) was significantly greater than expected values based on carrier application rates (2–7%), irrespective of carrier.