Assessing crop residue cover when scene moisture conditions change

Crop residues protect the soil against erosion and reduce agrochemicals in runoff water. Crop residues and soils are spectrally different in the absorption features associated with cellulose and lignin. Our objectives were to: (1) assess the effects of soil and crop residue water contents on the remotely sensed estimates of crop residue cover and (2) propose a method to mitigate these effects. Reflectance spectra of diverse crops and soils were acquired in the laboratory and the analyses was extended to agricultural fields with different crop residue covers and a wide range of moisture conditions. The slope of the linear relationship with the Cellulose Absorption Index was very sensitive to moisture conditions, whereas the slope of the Shortwave Infrared Normalized Difference Residue Index was altered in a lesser extent. Water indices that provided reliable estimates of the water content could be used to estimate crop residue cover corrected by moisture conditions.