Abstract
Most rhizobial inoculants that stimulate legume yield are applied with carriers that enhance root contact. The physicochemical properties of biochar are suitable for microbial growth, and it could be an alternative to peat, which comes from decreasing reserves but is the commonest solid inoculant carrier. The aim of the current research was to evaluate biochars as carriers of bradyrhizobia in solid inoculant and as coatings for seeds. Biochars and peat were inoculated with Bradyrhizobium japonicum strain 532C and storage time was assessed. A seed coating system was developed using biochar, bacteria liquid culture, water, and guar gum. The viability of bacteria in the coating and in solid biochar was evaluated at 4°C and 21°C. Two biochars were selected for a germination assay. Finally, greenhouse experimentation investigated the effect of biochar inoculant and seed coating on soybean growth and nutrient uptake. The storage time experiment showed that not all biochars equally sustain bacteria survival over time. The germination assay demonstrated that biochar seed coating had no effect on soybean germination. Greenhouse experimentation indicated that the effect of Pyrovac biochar on soybean growth characteristics and nutrient uptake depended on the fertilizer. The main finding was that biochar solid inoculant positively affected plant growth metrics, root characteristics, and the chemical composition of plants supplied with N-free nutrient solution.
Highlights
IntroductionIt can be produced using organic wastes such as agricultural residues, sewage sludge, or wood chips
A sudden decline in the population of B. japonicum was observed in BL and BQ biochars
Biochar was used as an inoculant carrier for B. japonicum as an alternative to peat moss
Summary
It can be produced using organic wastes such as agricultural residues, sewage sludge, or wood chips. Several properties of biochar suggest suitability as an inoculant carrier and seed-coating material. The physicochemical properties of biochar can sustain bacterial life: highly porous structure and surface area can be inhabited by bacteria and protect microorganisms from predation; high water holding capacity can prevent bacterial desiccation; reduced carbon is a potential source of energy, biochar can provide some mineral nutrients. Biochar production costs are usually low, it can be locally produced and available, and the use of it is environmentally safe. Other aspects of biochar that are important for potential applications in agriculture are the easiness of the sterilization process, inoculation, and seed coating preparation
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