Hydrologic and Vegetation Management Influence Oxygen Dynamics and Nitrogen Processing in Experimental Ditches

Author(s): Nifong, R.; Taylor, J.; Yasarer, L.

With increasing consumer demand for sustainable agricultural production and continued concern for coastal economies, excess nitrogen (N) runoff from agricultural areas remains a major challenge to reducing the environmental footprint of high intensity agriculture. To address this challenge, producers need simple and innovative approaches that reduce runoff from agricultural fields while maintaining high productivity. Agricultural ditches act as the primary water-soil interface on farms and are a pivotal, but currently underutilized, location to implement low-cost management practices to increase both on-farm and landscape-scale mitigation of excess N runoff. Previous small scale experiments have demonstrated good potential for rice cutgrass (Leersia oryzoides) to enhance both N uptake and denitrification in ditch sediments. However, it is unclear how small-scale mesocosm studies and core based methods translate to larger scale observations that incorporate diel patterns in light and temperature, both of which can influence primary production, O2 dynamics, and related N processing. To inform how ditch management may influence N dynamics at larger spatial and temporal scales, we examined how hydrologic and vegetation management practices interact to influence diel nitrogen and oxygen dynamics by experimentally manipulating hydrologic residence time and the presence of rice cutgrass (L. oryzoides) in six experimental ditches. We measured plant nutrient uptake, denitrification fluxes, and metabolism using in situ dissolved solute and gas sampling techniques over three 24 hour diel experimental runs. Results indicate that ditches with vegetation promote N retention and have more pronounced oxygen dynamics which can alter expected N removal pathways. We will discuss the complexities in outcomes of these management practices within the context of whole system measurements that incorporate diel cycles.

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