Synergistic effect of co-application of biochar and a PGPR, Bacillus cereus, on spinach yield under reduced chemical fertilizer regime

Excessive use of chemical fertilizers in agriculture contributes substantially to greenhouse gas emissions and underground water pollution. Therefore, there is an urgent need to reduce the use of chemical fertilizers without compromising agricultural productivity. Biochar and plant growth-promoting bacteria (PGPR) could be an environment-friendly and cheaper solution in this regard. We evaluated the effect of a sugarcane-bagasse derived biochar on Spinacia oleracea under 75% or 50% of the recommended fertilizers, in presence or absence of a PGPR i.e., Bacillus cereus. Spinach was grown on a sandy clay loam soil in pots for 60 days. Biochar was mixed at 1 or 2% (w: w basis) with soil in all possible combinations of 75% or 50% of the recommended fertilizers. Plants receiving 100% of recommended fertilizers served as control. Biochar significantly increased fresh leaf biomass, with the maximum increase of 152% found where 2% biochar + 75% fertilizer were added. Moreover, co-application of biochar with PGPR further increased the leaf biomass, with the maximum increase of 208% found when 2% biochar and PGPR were co-applied under 50% fertilizer regime. Biochar significantly increased the soil nitrate content, with the maximum increase of 529% found in 2% biochar addition under 50% fertilizer application. Co-application of PGPR and biochar further increased soil nitrate content with the maximum increase of 750% found in 1% biochar application under 75% fertilizer regime. Phosphorus availability was only increased by 1% biochar application with maximum increase of 250% under 75% fertilizer regime. Co-application of PGPR with 1% biochar increased the microbial biomass by 91% and 75% under 75% and 50% fertilizer application respectively. Principal component analysis showed that the soil nutrients i.e., nitrate, and available phosphorus and microbial biomass, which were overwhelmingly improved under co-application of biochar and PGPR, were closely related to spinach leaf and root biomass. We concluded that the co-application of biochar and the PGPR acted synergistically in increasing the nutrient availability for plants thereby leading to higher productivity. Therefore, we recommend that this technique can be a viable solution for reducing the input costs on fertilizer in addition to boosting plant productivity.