Intended and unintended impacts of nitrogen‐fixing microorganisms and microbial inhibitors on nitrogen losses in contrasting maize cropping systems

Abstract

Efforts to mitigate the nitrogen (N) footprint of maize production include using N‐fixing microbes (NFM) and/or microbial inhibitors. We quantified the effects of NFM, the nitrification inhibitor (NI) 2‐(N‐3,4‐dimethyl‐1H‐pyrazol‐1‐yl) succinic acid isomeric mixture, and the urease inhibitor (UI) N‐(n‐butyl) thiophosphoric triamide, each applied by itself or paired with another additive, on nitrous oxide (N2O) emissions, nitrate (NO3−) leaching, and crop performance in contrasting irrigated and rainfed maize systems over two growing seasons. We also used published emission factors to estimate indirect N2O emissions from leached NO3− that can be converted to N2O. Agronomic effects were relatively small; the NI + NFM treatment increased N use efficiency and grain yield and protein content in some cases by 11%–14% relative to a treatment receiving only urea. Most of the additive treatments reduced direct (in‐field) N2O emissions, most consistently for treatments that contained NI which reduced emissions by 24%–77%. However, these beneficial effects were counteracted by increased NO3− leaching, which occurred most consistently with UI or NFM applied as single additives or with NI. In these treatments, NO3− leaching increased during at least one growing season, and at both sites, by factors of 2–7. In three site‐years, increased NO3− leaching with NFM and NI + NFM offset large reductions in direct N2O, such that total direct + indirect N2O emissions were not different from that in the urea only treatment. These unintended effects may have resulted from unfavorable rainfall timing, varying crop N demand, and declining additive effectiveness. Use of these soil additives requires caution and further study.

Simulating Maize Response to Split-Nitrogen Fertilization Using Easy-to-Collect Local Features

“…When addressing climate change issues, fertilization decisions to tackle N 2 O emissions may show even greater leverage than soil C sequestration [8]. Microbial inhibitors do not appear to be a solution to tackle N 2 O emissions [9]. The rate of N fertilization should thus be reduced.…”