Use of biochar with immobilized free-living N-fixers as mineral fertilizer

Abstract

It is known that biochar application as soil fertilizer lead to reduce N loss. At the same time because of its porosity biochar is high quality substrate for immobilization microorganisms. The practice of using free-living N fixing bacteria (FLNFB) in organic farming is widely used to increase the nitrogen content in the soil. In this study immobilisation FLNFB on two types of biochar (made of chicken manure and sewage sludge) was applied to increase soil quality and crop productivity. The effectiveness of immobilization has been proven using SEM method: biofilms of FLNFB on the porous surface of both types of biochars are visible in the SEM images. The effectiveness of application 1% by mass biochar with FLNFB was estimated during 30 days vegetation experiment in greenhouse conditions by estimating the chemical composition of the soil (pH, CEC, OM, Corg, Ntot), by estimating change the functional activity of the soil microbial community (soil respiration activity, leucine aminopeptidase enzyme activity), by estimating change the structure of the microbial community (qPCR were used to analyze nifH and 16S rRNA genes in order to study the total count of bacterial and fungi), by estimating change the plants characteristics (chlorophyll content, germination, root and shoot length, biomass). It was found that application biochar with FLNFB lead to higher content of Ntot (0.11-0.19%) in soil in the end of the experiment as comparing than that for soil samples with mineral fertilizer ( 0.09%) and control soil (0.08%). The application biochar with FLNFB lead to significantly increase nifH-genes in soil. The soil leucine aminopeptidase and respiration activity have a similar trend for samples with and without biochar. The use of biochar as fertilizer led to increase chlorophyll content (13-22%) and barley biomass (10-84%) and decrease the length of the root (3-33%) in comparison with the control soil.