In the Chesapeake Bay region, conservation tillage is an important best management practice that is often emphasized in watershed implementation plans designed to meet water-quality objectives. Conservation tillage maintains crop residue on the soil surface, protecting soils from wind and water erosion, reducing moisture loss, and increasing soil carbon storage. Traditionally, crop residue is assessed using in-field observations, but these methods are not cost-effective over large land areas, and stakeholders have a strong interest in tools to map the distribution of crop residue, and corresponding tillage intensity, throughout the agricultural landscape.
Satellite remote sensing can provide the ability to map crop residue at the landscape scale. However, crop residues and soils appear similar in the visible near-infrared spectrum, limiting the effectiveness of typical moderate resolution satellites for mapping tillage intensity. The WorldView-3 satellite is unique in providing eight reflectance bands in the shortwave infrared (SWIR), which can be used to measure cellulose and lignin adsorption features that appear around 2,200 nm, thereby providing a method to directly measure crop residue.
This project uses on-farm data collection to calibrate WorldView-3 SWIR imagery, accurately mapping springtime crop residue on non-vegetated fields (goodness of fit = 0.90). In 2017, USGS scientists extracted reflectance data from partially irrigated fields (center pivot irrigation was underway at the time of satellite overpass) and developed methods for correcting the calibrations to account for variability in soil moisture, which can strongly affect the reflectance signal.
USGS scientists also developed methods that use the results of the small-footprint WorldView-3 imagery analysis (12-km swath width) to accurately calibrate residue analysis within the larger footprint of Landsat imagery (185 km), providing capacity to map crop residue on non-vegetated fields across the entire Delmarva Peninsula.
These results are being combined with wintertime vegetation analysis on fields planted with winter cover crops, providing map-based analysis of the extent and performance of two important agricultural conservation practices.
Springtime map of the agricultural landscape based on WorldView-3 satellite imagery: shades of tan depict varying amounts of crop residue from bare soils to 100% cover.