Contrasting effects of inhibitors and biostimulants on agronomic performance and reactive nitrogen losses during irrigated potato production

Authors: SOUZA, EMERSON F.C. - UNIVERSITY OF MINNESOTA; ROSEN, CARL - UNIVERSITY OF MINNESOTA; Venterea, Rodney - Rod

Submitted to: Field Crops Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/3/2019
Publication Date: 5/22/2019
Citation: Souza, E., Rosen, C., Venterea, R.T. 2019. Contrasting effects of inhibitors and biostimulants on agronomic performance and reactive nitrogen losses during irrigated potato production. Field Crops Research. 241:1-11. https://doi.org/10.1016/j.fcr.2019.05.001.
DOI: https://doi.org/10.1016/j.fcr.2019.05.001

Interpretive Summary: Urea is the dominant nitrogen (N) fertilizer used globally and is widely applied to N-intensive crops including potato (Solanum tuberosum L.). Various amendments have been marketed for co-application with urea to improve crop performance and/or reduce reactive N losses. Few if any studies have compared amendments that inhibit microbial processes with those designed to enhance microbial activity, and few have simultaneously quantified N losses as both nitrate (NO3-) and nitrous oxide (N2O). We quantified effects of two nitrification inhibitors (DCD and DMPP), alone or combined with a urease inhibitor (NBPT), and a N-fixing microbial (NFM) product, alone or combined with microbial enhancing (ME) organic compounds, on potato performance, NO3- and N2O losses, and soil N availability during the 2015 and 2016 growing seasons in an irrigated loamy sand in Minnesota. We also evaluated crop and NO3- leaching responses to varying N rates in the absence of amendments, used NO3- leaching to derive total (direct+indirect) N2O emissions, and evaluated N surplus as a N loss index. Across all treatments, N surplus explained 45-65% of the variance in reactive N losses in 2015, but only 12-32% of the variance in 2016. The N surplus-NO3- leaching relationship exhibited high variability across growing seasons, indicating that these relationships may not be widely generalizable. Both inhibiting and enhancing amendments had small (7-13%) beneficial effects on crop yield and/or N uptake, but these effects were not consistent across growing seasons or N rates. The DMPP+NBPT combination had the most consistent effect on NO3- leaching, with reductions of 12-38%, whereas DCD+NBPT did not reduce, and in some cases increased, NO3- losses, even though DCD was applied at a 10-fold greater rate than DMPP, indicating an advantage of DMPP over DCD. In contrast to the inhibitors, which consistently decreased N2O by 27-53% compared to urea alone, NFM and NFM+ME increased total, area- and yield-scaled N2O emissions by 20-39% across growing seasons. The NFM amendments also increased NO3- losses in some cases. Microbial enhancers may have unintended impacts on reactive N losses that need additional study to determine their costs and benefits under a variety of climate, crop and soil conditions. These findings will be of interest to producers and policy makers interested in developing improved practices that enhance crop production while decreasing losses of N to the environment.

Technical Abstract: Urea is the dominant nitrogen (N) fertilizer used globally and is widely applied to N-intensive crops including potato (Solanum tuberosum L.). Various amendments have been marketed for co-application with urea to improve crop performance and/or reduce reactive N losses. Few if any studies have compared amendments that inhibit microbial processes with those designed to enhance microbial activity, and few have simultaneously quantified N losses as both nitrate (NO3-) and nitrous oxide (N2O). We quantified effects of two nitrification inhibitors (DCD and DMPP), alone or combined with a urease inhibitor (NBPT), and a N-fixing microbial (NFM) product, alone or combined with microbial enhancing (ME) organic compounds, on potato performance, NO3- and N2O losses, and soil N availability during the 2015 and 2016 growing seasons in an irrigated loamy sand in Minnesota. We also evaluated crop and NO3- leaching responses to varying N rates in the absence of amendments, used NO3- leaching to derive total (direct+indirect) N2O emissions, and evaluated N surplus as a N loss index. Across all treatments, N surplus explained 45-65% of the variance in reactive N losses in 2015, but only 12-32% of the variance in 2016. The N surplus-NO3- leaching relationship exhibited high variability across growing seasons, indicating that these relationships may not be widely generalizable. Both inhibiting and enhancing amendments had small (7-13%) beneficial effects on crop yield and/or N uptake, but these effects were not consistent across growing seasons or N rates. The DMPP+NBPT combination had the most consistent effect on NO3- leaching, with reductions of 12-38%, whereas DCD+NBPT did not reduce, and in some cases increased, NO3- losses, even though DCD was applied at a 10-fold greater rate than DMPP, indicating an advantage of DMPP over DCD. In contrast to the inhibitors, which consistently decreased N2O by 27-53% compared to urea alone, NFM and NFM+ME increased total, area- and yield-scaled N2O emissions by 20-39% across growing seasons. The NFM amendments also increased NO3- losses in some cases. Microbial enhancers may have unintended impacts on reactive N losses that need additional study to determine their costs and benefits under a variety of climate, crop and soil conditions.