| In recent years,microbial pesticides,represented by Bacillus thuringiensis（Bt）,have been widely used in modern agriculture.However,the use of microbial pesticides is limited by their short effective period and susceptibility to environmental influences.Biochar,which has advantages in loading microorganisms,slow-release of chemical pesticides and fertilizers in farmland,has been proposed as a carrier for microbial pesticides in order to develop a new type of charcoal-bacteria coupling agent.In this study,biochar was used as a carrier to prepare a charcoal-bacteria coupling agent with high efficiency,long effective period,stability,low cost,and environmental friendliness,by studying the pyrolysis temperature and modification methods of biomass raw materials.The bioactivity and release pattern of NBIN863loaded on biochar were determined to explore the mechanism of enhancing the efficiency of microbial pesticides.This study provides theoretical support and technical guidance for the development of new types of microbial pesticide formulations,the resource utilization of agricultural waste,and the efficient utilization of microbial pesticides:（1）During the fermentation process of NBIN863 in LB medium,it was necessary to grow from the nutritional form to the more stable spore form,which required 48 h.Based on the growth curve of NBIN863 and its insecticidal mechanism,the use of biochar loading was initiated at 24 h of fermentation and the charcoal bacterial coupling agent was isolated at 48 h to ensure the optimal loading effect.Furthermore,the toxicity of NBIN863 spores to Meloidogyne incognita was verified.（2）The biochar RS6,prepared from rapeseed straw at 600℃,had a more developed pore structure and a surface with abundant functional groups suitable for NBIN863 colonization.The biochar was found to be the most suitable carrier for NBIN863 with a maximum load of 7.57×109 CFU/g.Morphological and biological activity tests of the RS6-coated microbial preparation showed that the majority of the NBIN863,which was immobilized on the biochar,remained in a stable spore form and displayed high toxicity against the nematode Caenorhabditis elegans.These results suggest that the biochar-coated NBIN863 is a promising new type of microbial pesticide formulation.（3）To further enhance the concentration of NBIN863 on the biochar carrier of the carbon-bacteria coupling agent for modification by RS6,the use of Na OH-modified biochar carrier can increase the NBIN863 concentration on the carbon-bacteria coupling agent by 2.31×1010 CFU/g with an increase of 205.3%.The concentration on the biochar carrier modified by HCl and Mg（OH）2 was slightly increased by 11.4%and reduced 56.8%relative to RS6,while the concentration on the biochar carrier modified by Mg Cl2 was significantly inhibited,with only 12.3%on the RS6 biochar carrier.Physicochemical analysis of the biochar shows that Na OH-modified biochar has better pore structure and larger average pore size than the original biochar,which is suitable for NBIN863 colonization.The abundant oxygen functional groups on its surface can provide more adsorption sites for NBIN863.However,the surface Mg2+on the biochar inhibits the growth of NBIN863.（4）The shelf life and sustained-release effector of charcoal fungus-coupled preparation were tested,and the results showed that the charcoal fungus-coupled preparation had a shelf life of 3 months at a storage temperature of 25℃,and over 6months at storage temperatures of-20℃and 4℃.The charcoal fungus-coupled preparation can also extend the effective period of NBIN863 in soil.Among them,the charcoal fungus-coupled preparation obtained by the 600℃pyrolysis of rapeseed straw had the best effect,and the effective concentration in the soil reached 765 times that of the control group 6 months later.Furthermore,in the leaching test,the sustained-release period of the charcoal fungus-coupled preparation was more than 3times that of the wettable powder,achieving efficient loading and sustained-release of NBIN863. |
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