Estimating Winter Cover Crop Nitrogen Uptake with Satellite Imagery: Four Years of Results From the Choptank River.

The Choptank River Watershed Conservation Effects Assessment Project (CEAP) has now accumulated a four-year set of quarterly SPOT satellite images taken over the Eastern Shore of the Chesapeake Bay watershed. Imagery collected in December and March of each year were used to estimate the productivity and nutrient uptake associated with 2390 farm fields that were enrolled in Maryland Agricultural Cost Share (MACS) programs for winter cover crops between 2005 and 2009. Agronomic data for each field (planting date, planting method, species, previous crop) were provided by MACS documentation, and on-site sampling of approximately 90 on-farm locations per image date were used to calibrate the correlation between satellite NDVI and aboveground cover crop biomass, to measure tissue nitrogen concentrations, and to observe cover crop effects on residual soil nitrate.  Results show significant reduction in nutrient uptake efficiency when compared to optimal management, with performance reductions largely affected by late planting dates and species choice.  Results can be used to calculate watershed nitrogen uptake associated with winter cover crops on a watershed basis, to improve cover crop implementation strategies, and to calculate the observed dollar costs per kilo of N sequestered for various cover cropped fields and locations.