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

Abstract

There is currently much interest in developing crop management practices that will decrease N 2 O emissions from agricultural soils. Many different approaches are being investigated, but to date, no studies have been published on how microbial inoculants affect N 2 O emissions. Th is study was conducted to test the hypothesis that microbial-based inoculants known to promote root growth and nutrient uptake can reduce N 2 O emissions in the presence of N fertilizers under controlled conditions. Carbon dioxide and CH 4 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- NH 4 NO 3 32% N (UAN), and an unfertilized control. Emissions of N 2 O and CO 2 were determined from soil incubations and analyzed with gas chromatography. Aft er 29 d of incubation, cumulative N 2 O emissions were reduced 80% by SB and 44% by SBF in soils fertilized with UAN. Treatment with Bacillus spp. signifi cantly reduced N 2 O production on Days 1 and 2 of the incubation in soils fertilized with UAN. In the unfertilized treatment, cumulative emissions of N 2 O were signifi cantly reduced 92% by SBF. Microbial-based treatments did not reduce N 2 O emissions associated with urea application. Microbial-based treatments increased CO 2 emissions from soils fertilized with UAN, suggesting a possible increase in microbial activity. Overall, the results demonstrated that microbial-based inoculants can reduce N 2 O emissions associated with N fertilizer application, and this response varies with the type of microbialbased inoculant and fertilizer. © American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America.