Carbon and Field-Scale Nitrate Flux Modeling Across Wide Climate Gradients and Diverse Soil Variability in the Dry-Land Agricultural Region of the Inland Pacific Northwest.

Mitigation strategies to minimize the loss of soil carbon and nitrogen require a fundamental understanding of the dominant hydrologic flow paths and runoff generating processes in a landscape.  In the dry-land agricultural region of the Inland Pacific Northwest steep, convergent topography often underlain by argillic soil horizons can result in unique spatial and temporal runoff and soil moisture patterns across a landscape.  With improved precision agriculture technology there are new opportunities to implement field-scale management practices to quantify carbon losses and minimize N₂O emissions and nitrate export.  However there is a lack of tools which can capture the field-scale variability in hydrology and sediment transport necessary to effectively quantify the impacts of mitigation strategies on carbon and nitrogen losses.   In this study we test the ability of the Soil Moisture Routing (SMR) model and the Water Erosion Prediction Project (WEPP) model to simulate field scale variability in the soil moisture, temperature, surface saturation, and soil erosion from two ~10 ha field catchments managed under no-till and conventional tillage practices, respectively.  Model assessment is based on both surface runoff and sediment load measured at the outlet of these field catchments and distributed measurements capturing spatial variability within the catchments.  We demonstrate how the accurate representation of the field scale variability in hydrology is an essential first step in the development of full scale cropping models capable of evaluating precision-based mitigation strategies.