Spatial variability of denitrification enzyme activity and actual denitrification emissions on Missouri claypan soils

Authors: JOHNSON, FRANK - University Of Missouri; LERCH, ROBERT - Retired ARS Employee; MOTAVALLI, PETER - National Institute Of Food And Agriculture (NIFA); Veum, Kristen; SCHARF, PETER - University Of Missouri

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/2/2021
Publication Date: 6/30/2022
Citation: Johnson, F.E., Lerch, R.N., Motavalli, P.P., Veum, K.S., Scharf, P.C. 2022. Spatial variability of denitrification enzyme activity and actual denitrification emissions on Missouri claypan soils. Soil Science Society of America Journal. 86(6):1582-1596. https://doi.org/10.1002/saj2.20457.
DOI: https://doi.org/10.1002/saj2.20457

Interpretive Summary: Greenhouse gas production can be impacted by several factors, including land management decisions and site-specific characteristics such as climate and soil type. Therefore, it is important to understand how agricultural management practices interact with the landscape to impact the process of denitrification to produce nitrous oxide, a potent greenhouse gas. This study assessed denitrification potential and spatial patterns of nitrous oxide flux in degraded claypan soils under contrasting crop management systems. Emissions from both cropping systems were dominated by nitrogen gas (> 85%) rather than nitrous oxide. In addition, this study indicated that long-term erosion patterns across the landscape exerted more control over denitrification than management practices. This study benefits scientists and producers by highlighting the importance of landscape level factors that may influence greenhouse gas production from agricultural systems.

Technical Abstract: Denitrification in agricultural soils is responsible for the majority of anthropogenic nitrous oxide (N2O) production. The objective of this research was to assess denitrification potential and the spatial dependence of soil N2O flux from soils under contrasting crop management in the Central Claypan Region of Missouri. Surface soil samples (0-10 cm) were collected on a 90-m grid from two claypan fields, one conventionally managed in a corn-soybean rotation with tillage and the other managed as a corn-soybean-wheat rotation with no-till and cover crops. Potential denitrification rates were measured using the denitrification enzyme activity protocol and actual denitrification rates of N2O and N2 were measured with the N-free atmospheric recirculation method. Potential denitrification rates were not significantly different between fields, but they were 77 and 72% greater in the toeslope position (p < 0.05) compared with the summit and backslope positions, respectively. Actual denitrification was dominated by N2 (> 85%) rather than N2O emissions across both fields. Actual N2, N2O, and total denitrification (N2 + N2O) fluxes were not different between fields, and only total denitrification flux showed an effect of landscape position similar to that of denitrification potential, with the backslope exhibiting lower emissions than the summit and toeslope. Although the high smectitic clay content of upland soils provides environmental conditions suitable for denitrification, these results indicate that long-term erosion patterns and the accumulation of soil C in the toeslope position controlled potential and actual denitrification rates. In addition, results from this study support the possibility that chemoautotrophic bacteria may significantly contribute to denitrification in claypan soils.