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Microbial-Based Inoculants Impact Nitrous Oxide Emissions from an Incubated Soil Medium Containing Urea Fertilizers

Pamela Calvo, Dexter B. Watts, Robert N. Ames, Joseph W. Kloepper, H. Allen Torbert
Journal of environmental quality 2013 v.42 no.3 pp. 704-712
aerobic conditions, aerobiosis, agricultural soils, anaerobic conditions, carbon dioxide, crop management, fertilizer application, gas chromatography, greenhouse gas emissions, microbial activity, nitrous oxide, nutrient uptake, plant growth-promoting rhizobacteria, root growth, soil quality, urea, urea fertilizers
There is currently much interest in developing crop management practices that will decrease N₂O emissions from agricultural soils. Many different approaches are being investigated, but to date, no studies have been published on how microbial inoculants affect N₂O emissions. This study was conducted to test the hypothesis that microbial-based inoculants known to promote root growth and nutrient uptake can reduce N₂O emissions in the presence of N fertilizers under controlled conditions. Carbon dioxide and CH₄ fluxes were also measured to evaluate microbial respiration and determine the aerobic and anaerobic conditions of the incubated soil. The microbial-based treatments investigated were SoilBuilder (SB), a metabolite extract of SoilBuilder (SBF), and a mixture of four strains of plant growth-promoting Bacillus spp. Experiments included two different N fertilizer treatments, urea and urea–NH₄NO₃ 32% N (UAN), and an unfertilized control. Emissions of N₂O and CO₂ were determined from soil incubations and analyzed with gas chromatography. After 29 d of incubation, cumulative N₂O emissions were reduced 80% by SB and 44% by SBF in soils fertilized with UAN. Treatment with Bacillus spp. significantly reduced N₂O production on Days 1 and 2 of the incubation in soils fertilized with UAN. In the unfertilized treatment, cumulative emissions of N₂O were significantly reduced 92% by SBF. Microbial-based treatments did not reduce N₂O emissions associated with urea application. Microbial-based treatments increased CO₂ emissions from soils fertilized with UAN, suggesting a possible increase in microbial activity. Overall, the results demonstrated that microbial-based inoculants can reduce N₂O emissions associated with N fertilizer application, and this response varies with the type of microbial-based inoculant and fertilizer.