MEASURING CROP RESIDUE COVER USING REMOTE-SENSING TECHNIQUES

Crop residues are managed under conservation tillage programs to leave as much as possible on the surface for minimization soil erosion and for improving water quality. Because current methods for measuring cro p residue cover are tediuous and somewhat subjective, there is a need for new methods to measure residue cover that are rapid, accurate, and objective. We discuss the potential for discriminating crop residues from soils using reflectance and fluorescence techniques and examine e xperimentally the changes in wheat residue fluorescence during weather ing. The fluorescence of crop residue was a board band phenomenon with emissions extending from 420 to 600 nm for excitation of 350-420 nm. Soils had low intensity broad band emissions over the 400-690 nm regio n for excitations of 300-600 nm. We found that the fluorescence intens ities for the crop residues were much greater than the fluorescence of the soils, but as the crop residues decompose, their blue-green fluor escence intensities approach the fluorescence of the soils. We conclud e that fluorescence techniques are less ambiguous and better suited fo r discriminating crop residues from soils than the reflectance methods . However, the potential problems, that must be addressed to implement the fluorescence technique, are (i) adequate excitation energy must b e supplied to induce fluorescence and (ii) the fluorescence signal is small relative to normal, ambient sunlight. Nevertheless, if properly implemented, we believe that the fluorescence techniques can be used t o quantify crop residue cover in field.