Microbial Inoculants As Tools for Reducing Nitrous Oxide Emissions From Soil.

Over the past few decades, emissions of nitrous oxide (N₂O) have increased worldwide due to several factors, including increases in cultivated crop area, use of synthetic nitrogen fertilizers, and livestock production. New management tools are needed to reduce N₂O emissions from production agriculture. One potential tool for this goal is the use of microbial inoculants, which are increasingly used in agriculture. The present study compared emissions of N₂O and CO₂ following applications of microbial based products to soil under controlled conditions. Treatments consisted of SoilBuilder (SB), a metabolite extract of SoilBuilder (SBF), and a mixture of plant growth-promoting rhizobacteria (PGPR).  Experiments included four different nitrogen fertilizers (urea, urea ammonium nitrate 32% N (UAN), calcium ammonium nitrate 17% N (CAN) and ammonium nitrate) and a no-fertilizer control.  After 29 days of evaluation, all microbial treatments reduced N₂O production from soils fertilized with CAN and UAN but not soils fertilized with urea or ammonium nitrate. Emissions of N₂O were reduced by 80.7% with SBF in soil treated with CAN and by 42.7% with SB in soil treated with UAN. Overall, emissions of CO₂ were increased by microbial treatments in soils with all four fertilizers, indicating that microbial activity was increased. Overall, the results of this study demonstrate that microbial inoculants can reduce emissions of N₂O associated with nitrogen fertilizer application, but this response varies with the type of microbial inoculant and fertilizer.  Future studies are needed to confirm the results under greenhouse and field conditions.