Location: Soil and Water Management ResearchTitle: Intended and unintended impacts of nitrogen-fixing microorganisms and microbial inhibitors on nitrogen losses in contrasting maize cropping systems
|SOUZA, EMERSON - University Of Minnesota|
|ROSEN, CARL - University Of Minnesota|
|Venterea, Rodney - Rod|
|MUHAMMAD, TAHIR - University Of Minnesota|
Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/21/2023
Publication Date: 6/30/2023
Citation: Souza, E., Rosen, C., Venterea, R.T., Muhammad, T. 2023. Intended and unintended impacts of nitrogen-fixing microorganisms and microbial inhibitors on nitrogen losses in contrasting maize cropping systems. Journal of Environmental Quality. Article 20500. https://doi.org/10.1002/jeq2.20500.
Interpretive Summary: Corn production is a primary target for decreasing the impacts of agriculture on the environment. Growing corn can promote emissions of nitrous oxide, which is an ozone-depleting greenhouse gas, and leaching of nitrate, which is a water pollutant. Efforts to minimize these impacts include applying nitrogen-fixing bacteria to reduce the need for fertilizer inputs or applying microbial inhibitors to slow down the processes in soil that produce nitrous oxide and nitrate. However, the impacts of these additives in corn production systems have not been assessed. Also, few studies have measured both nitrous oxide and nitrate in the same experiment. Here, we measured these effects in both an irrigated coarse-textured soil and in a rainfed medium-texture soil over two years in Minnesota. We found that one of the microbial inhibitors that inhibits nitrification consistently reduced nitrous oxide emissions by 24% to 77%. However, another microbial inhibitor that inhibits urea hydrolysis, and the nitrogen-fixing microbes, both increased nitrate leaching by a factor of 2 to 7. We conclude that applying these additives can have unintended consequences and requires further study to optimize their use. These results will have implications for scientists, land managers and policy makers interested in reducing the impact of corn production on air and water quality.
Technical Abstract: Due to its widespread production and high demand for nitrogen (N) inputs, the maize (Zea mays L.) agroecosystem is a primary target for mitigating the global N footprint of agriculture. Recent efforts include applying N-fixing microbes (NFM) as a supplemental N source and/or microbial inhibitors to enhance N use efficiency. However, the impacts of NFM on reactive N losses in maize production systems have not been assessed, and few studies have measured N losses in both gaseous and soluble forms. Here, we quantified the effects of NFM, the nitrification inhibitor DMPSA, and the urease inhibitor NBPT, each applied by itself or paired with another additive, on nitrous oxide (N2O) emissions, nitrate (NO3-) leaching, and crop performance in two contrasting urea-fertilized systems, an irrigated coarse-textured soil (IC) and a rainfed medium-texture soil (RM) over two growing seasons. When DMPSA was co-applied with urea, either by itself or paired with NFM or NBPT, N2O emissions were reduced in all four site years by 24-77% compared to non-supplemented urea, while NFM or NBPT applied as single additives reduced N2O emissions by 28-56% in only two site years. When NFM and NBPT were applied, either as single additives or together with DMPSA, leaching of NO3- increased in both systems during at least one growing season by a factor of 2 to 7. In two site-years, the magnitude of NO3- leaching observed with NFM and NFM + DMPSA more than offset the reduction in N2O emissions, such that total direct + indirect N2O emissions were greater compared to urea alone. Agronomic effects were modest, with NFM + DMPSA increasing grain yield by ~12% in the RM system. While DMPSA, alone or paired with NBPT, reduced total direct + indirect N2O emissions in three of four site years, unfavorable timing of rainfall events, varying crop N demand, and duration of additive effectiveness may have combined to cause unintended increases in reactive N losses when NFM and NBPT were applied.