Assessment of spectral indices for crop residue cover estimation

The quantification of surficial crop residue (nonphotosynthetic vegetation) cover is important for assessing agricultural tillage practices, rangeland health, and brush fire hazards. The Cellulose Absorption Index (CAI) and the Shortwave Infrared Normalized Difference Residue Index (SINDRI) are two spectral indices that have shown promise for remote estimation of crop residue cover. CAI and SINDRI utilize three and two spectral bands, respectively, rendering the latter less expensive to implement in future satellite sensors. This study shows that while CAI always contrasts well among soils, crop residues, and live vegetation, this is not always the case for SINDRI. A small number of surficial soil samples had positive SINDRI values that have reduced contrasts among crop residues. Some of these soils were biased by SINDRI-positive component minerals. As such, SINDRI is less applicable for remote crop residue cover estimation, even with reduced implementation costs.