Remote sensing of crop residue cover and soil tillage intensity

Crop residues on the soil surface reduce soil erosion and affect water infiltration, evaporation, and soil temperatures. Crop residues also influence the flow of nutrients, carbon, water, and energy in agricultural ecosystems. Current methods of measuring crop residue cover are inadequate for monitoring large areas. One promising remote sensing approach for discriminating crop residues from soil is based on a broad absorption band near 2100 nm that appears in plant materials and is absent in most soils. The cellulose absorption index (CAI), which measured the relative depth of this absorption feature, was linearly related to crop residue cover. High-altitude AVIRIS data acquired on 11 May 2000 prior to spring crop planting at the Beltsville Agricultural Research Center in Maryland were analyzed. NDVI was calculated using bands centered at 827 nm and 646 nm and CAI was calculated using bands at 2031, 2101, and 2211 nm. Agricultural fields with low green vegetation cover (low NDVI) were classified into three tillage categories based on crop residue cover determined by CAI. Fields with >30% residue cover were classified as conservation tillage; those with 15-30% residue cover as reduced tillage; and those with <15% residue cover as intensive tillage. The tillage classification agreed with ground observations in corn harvested for grain and tilled fields. Soybean fields and mowed alfalfa fields had low residue cover even with no tillage. Thus, both residue cover and previous crop type are necessary to classify tillage intensity in agricultural fields.