Effect of Microbial Inoculation on Nitrogen Plant Uptake and Nitrogen Losses from Soil and Plant-Soil Systems

Abstract

Reducing the negative impacts of agricultural fertilizers is a world-wide concern, both from an environmental and human health perspective. One way to reduce these impacts is by enhancing plant uptake, which improves nutrient use efficiency, thereby reducing the amounts of fertilizer needed. The general objective of this research was to evaluate the effect of microbial- based inoculants on nitrous oxide (N2O) emissions from plant and soil systems and their effect on enhancing plant nitrogen uptake. Specific objectives were: i) to evaluate the effect of microbial inoculants (PGPR mixture (BM), Soil Builder™ product (SB), and Soil Builder™ product filtrated (SBF)) on N2O emissions from soil in a jar incubation study using different types of nitrogen (N) fertilizers; ii) to evaluate and confirm the effect of the same microbial inoculants on N2O emissions when a plant is present in the system in a greenhouse study using different types of N fertilizers; iii) to understand the effect of microbial inoculants on corn growth, nutrient uptake, and root morphology of corn evaluated at different growth stages and with different types of N fertilizers; iv) to identify the best PGPR Bacillus spp. mixture that has with the potential to reduce N fertilization and obtain results comparable to a 100% N recommended fertilization, and v) Determine if selected mixture of PGPR increase plant growth and transcript levels of nitrate and ammonium uptake genes of Arabidopsis thaliana . Emissions of N2O were reduced by 62% on average with SBF and SB in soil treated with calcium ammonium nitrate (CAN) and by 66% on average with SB, SBF, and BM in soil treated with urea ammonium nitrate (UAN). In the greenhouse study, cumulative fluxes of N2O from pots at 41 DAP showed a significant reduction of 37% (BM) and 23% (SBF) with CAN fertilizer. When UAN was used, reductions of 26% (SB), 28% (SBF), and 49% (BM) were obtained. However, no reduction of N2O was reported with urea fertilizer. Corn growth parameters (height, shoot fresh and dry weight) and nutrient uptake were increased in corn plants treated with microbial inoculants, and the differences were greatest in plants evaluated at VT stage. Total root length, root volume, and root surface were increased at the V2 and V4 stages in plants with microbial inoculants. Three PGPR mixtures reduced N fertilization on when fresh weight (16%), dry weight (1.5%), and nitrogen uptake (6.64%), were evaluated in cabbage. Greater reduction of N fertilization was observed in pepper where PGPR mixtures allowed reductions of 30.46% (fresh weight), 30.03%, (dry weight) and 26.93% (nitrogen uptake). Plant growth parameters of A. thaliana were increase by PGPR mixtures. Transcript levels of 5 of the six nitrate uptake genes and four of the five ammonium uptake genes evaluated in roots were increased by PGPR mixtures. Overall, the results demonstrate that microbial inoculants can reduce emissions of N2O resulting from some types of nitrogen fertilizers and can increase plant growth and plant nutrient uptake, thereby reducing nitrogen fertilization.