In the Chesapeake Bay Watershed, the use of winter cover crops on agricultural land has been identified as a priority conservation practice for improving soil health and reducing the loss of nutrients and sediment from farmland. Winter cover crops (such as rye, barley, wheat, and radish) are planted in the fall, following the harvest of summer row crops (such as corn, soybean, vegetables). The cover crops are typically killed the following spring to release nutrients for the subsequent cash crop. Winter cover crops take up nitrogen that would otherwise be vulnerable to leaching over the winter, and they protect the soil from raindrop impact and erosion. Because they help meet important environmental targets, cover crops are strongly promoted by agricultural conservation agencies in the Chesapeake Bay region, and their use on farms has rapidly increased over the past decade. However, on-farm performance has been shown to be highly variable, and the effects on water quality are not well quantified.
This project uses multispectral satellite imagery to measure wintertime vegetation on agricultural fields and combines this information with site-specific knowledge of crop rotations and cover crop management practices. Proximal sensors and on-farm sampling are used to calibrate imagery interpretation, and hyperspectral biophysical models are used to understand the impact of various components of ground cover (vegetation, soils, crop residue, and shadow) on field reflectance. Using these methods, USGS researchers can map cover crop performance at the watershed scale and improve the understanding of conservation outcomes associated with various cover crop management strategies. This information is used by farmers and conservation agencies to promote adaptive management of winter cover crop programs to maximize environmental benefits. Scientific challenges include maintaining consistent calibration for satellite imagery interpretation from image to image across time, as well as accounting for the effects of soil moisture and background soil reflectance to accurately measure low levels of vegetation.
Wintertime biomass on agricultural fields following corn harvest, Talbot County, Maryland, showing the distribution of fields with minimal to high levels of vegetation.