Effect of Biochar and Bradyrhizobium japonicum Inoculation on AMF Colonization, Phosphorus up-take and Biological Nitrogen Fixation (BNF) of Soybean [Glycine max (L.)] At Jimma, Southwest Ethiopia

Abstract

Phosphorus deficiency is one of the most important soil factors, which affect soybean growth and its productivity. Biochar is one of the most important and easily available soil amendment resources that can improve soil properties and help plant roots access to mycorhyzal fungi. Nodulation and nitrogen fixation capacity of soybeans is affected by the extent to which the plant forms symbiosis with Bradyrhizobium japonicum. However, there are still many uncertainties about biochar, particularly whether it has positive effects with a particular soil and crop type. This study was, therefore, conducted to determine the effect of biochar application rate and Bradyrhizobium japonicum inoculation on Arbuscular Mycorhyzal Fungi (AMF) colonization, P uptake and Biological Nitrogen Fixation (BNF) of soybean (Glycine max) grown on Nitisol of Jimma, south-west Ethiopia. The experiment was conducted under greenhouse condition from February 2016 to May 2016 in randomized complete block design with three replications. The treatments consisted of four levels of biochar application rates (0, 6, 12 and 36 ton/ha with and without P supplement) with and without Bradyrhizobium japonicum strain (MAR1495) inoculation. Data on growth and yield parameters, AMF colonization, BNF and P up-take were collected and statistically analyzed using SAS 9.2 software. Analysis of Variance showed that application of biochar and B.japonicum inoculation had significant (P<0.05) effect on all parameters. Applications of 36 t ha-1 of biochar supplemented with 100kg/ha DAP showed a significant increase in all growth and yield parameters in both inoculated and non-inoculation treatments. Moreover, P uptake (4.81 and 4.27 g plant-1 ), total N (4.19 and 2.66 g/plant), N2 fixation (4.61 and 2.98 g plant-1 ) and % Nitrogen derived from atmosphere (98.57 and 97.74) were also improved at 36 t ha-1 of biochar supplemented with 100kg/ha DAP in both inoculated and non-inoculation plots, respectively. Whereas inoculated treatments performed better as compared to the noninoculated treatments for all the parameters. However AMF colorizations (79.79 and 78.65%) with and without inoculation, respectively, were significantly higher in a treatment containing of 36 t ha-1 biochar alone. The amount of N2 fixed by soybean, and total N and P uptake were strongly and significantly correlated with number of nodules and total colonization of soybean. The results confirmed that biochar application with B.japonicum inoculation was beneficial for soybean growth, N and P up-take and BNF. Hence, application of 36 t ha-1 biochar with inoculation and P supplementation was considered as effective for soybean growth, BNF and P up-take. However, AMF root colonization percentage was high at 36 t ha-1 biochar without P supplement.