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The influence of flood timing, crop rotation, and soil properties on net N2 flux from temporarily flooded agricultural fields
Proceedings of the 2023 Mississippi Water Resources Conference

Year: 2023 Authors: Powell J., Simek V., Rosson A., Taylor J., Moore M.

Nitrogen (N) is a vital nutrient necessary for all living organisms. The bulk of N is in N2 gas and not bioavailable. Bacteria facilitate natural fluxes of N from the atmosphere to the biosphere and back through nitrogen fixation and denitrification, maintaining a balanced nitrogen cycle. However, increased fertilizer production and cultivation of N fixing crops has led to excess N in the environment and runoff of excess N from agricultural and urban landscapes can cause many problems, including harmful algal blooms and hypoxia which degrade aquatic habitats. Managing fallow agricultural land in the Mississippi Delta for wildlife wetland habitat in fall and winter can enhance wetland properties that promote denitrification. We collected sediment cores from flooded agricultural fields across ten farms representing different timing of flooding, crop rotations, and soil properties, and incubated them using the same source water to assess how different factors influence N2 flux rates during flooding. We collected water samples from core inflow and outflow lines and measured N2:Ar and O2:Ar ratios using membrane inlet mass spectrometry (MIMS). Net N2 flux and sediment O2 demand were estimated for 30 cores representing replicates from the 10 farms.We then extracted the upper 5cm of the sediment core for characterization of particle size, organic matter content, and carbon, nitrogen and phosphorus concentrations, as well as later DNA extraction to characterize microbial communities. We will present results that seek to link crop rotation, sediment properties, and flooding duration to net N2 flux rates. Understanding how crop rotation, soil properties, and timing of flooding influence N2 flux in agricultural fields managed for fall/winter wetland wildlife habitat can help identify how the nutrient mitigation potential of these conservation practices varies across different conditions throughout the Delta and provide managers with novel ways of managing excess nitrogen in agricultural watersheds.

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