Discriminating crop residues from soil by reflectance and fluorescence techniques

Crop residues, the portion of the crop left in the field after harvest, can be an important factor in controlling soil erosion. Current methods for quantifying percent crop residue cover are tedious and somewhat subjective. There is a need for new methods to quantify residue cover that are rapid, accurate, and objective. Reflectance and fluorescence spectra of recently-harvested and weathered corn, soybean, sorghum, and wheat residues plus 36 agricultural soils were measured. The reflectance data showed that no single wavelength appears capable of uniquely distinguishing all soils from all crop residues. Crop residues may be brighter or darker than a given soil. The fluorescence of most of the crop residues was consistently greater than the fluorescence of most of the soils. The authors´ studies indicate that a fluorescence method may be less ambiguous and better suited for detecting crop residues on soils than reflectance methods