Effect of biochar in improving the nodulation, growth and yield of rhizobium inoculated ming bean (Vigna radiata L.)".

Abstract

Biochar is a carbon rich product and highly porous charcoal substance that is distinguished from other charcoals in its intended use as a soil amendment. Biochar can persist in soils for many centuries and has great potential to improve agronomic production when applied as a soil amendment. In this study, a number of rhizobial strains were isolated from the root nodules of mung bean from the different fields of Faisalabad. Fast growing rhizobial isolates were selected and were further screened for their ability to promote growth and nodulation of mung bean seedlings under axenic conditions. The four most effective isolates (MR1, MR3, MR4 and MR5) were selected to evaluate their potential to improve growth and nodulation in biochar-amended soil. Three different biochars (wheat straw (WSB), rice straw biochar (RSB) and cotton stick biochar (CSB)) were produced by slow pyrolysis at 350°C with 30 min residence time. Selected rhizobial strains (MR1, MR3, MR4 and MR5) with four levels of biochar (0, 0.5, 1.0 and 1.5%) were used to find the best combination of rhizobial strains and biochar. Rhizobial strains MR4 and MR5 at 1.0% biochar level successfully improved nodulation, and fresh and dry weight of mung bean. Regarding plant growth, overall response of CSB was greater than WSB and RSB. At 1.0% application rate, CSB resulted in better nodulation, and fresh and dry biomass than WSB- and RSB-amended treatments. On the basis of results obtained from this study, CSB at the 1.0% rate with rhizobial strains MR4 and MR5 were selected for a pot trial. The rhizobial strains were evaluated in pots amended with four levels of CSB (0, 0.5, 1.0 and 1.5%) for improving growth, nodulation and yield of mung bean plants. All these attributes were improved by increasing the concentration of biochar. However, better results were obtained at 1.0% biochar-amended soil. Rhizobial inoculation significantly improved the growth, physiology, photosynthesis, moisture contents, oil contents, fiber and chlorophyll contents of mung bean. Moreover, the combined effect of rhizobial inoculation and 1.0% biochar was better than their sole use. The selected rhizobial strains (MR4 and MR5) along with 1.0% biochar were also evaluated to study their effect on growth, nodulation, nitrogenase activity and soil microbial community composition. The growth, nodulation, nitrogenase activity, soil microbial biomoass C, N, P were significantly increased by the application of 1.0% CSB and rhizobial inoculation. However, more promising results were obtained due to their combined use. The combined application of rhizobia and biochar is an effective strategy to improve productivity of mung bean.