Measuring crop residue cover by fluorescence imaging

Crop residues, the portion of the crop left in the field after harvest, can be an important management factor in controlling soil erosion. Current methods for quantifying 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. Scenes with known amounts of crop residue were illuminated with long-wave ultraviolet (UV) radiation and fluorescence images were recorded with an intensified-video camera fitted with a 453-488 nm band-pass filter. Four agricultural soils ranging from light-gray to nearly black were used as backgrounds for the weathered soybean stems. Residue cover was determined by counting the proportion of the pixels in the image with fluorescence values greater than a threshold. Soil pixels had the lowest gray levels in the images regardless of the soil type. The values of the soybean residue pixels spanned nearly the full range of the 8-bit video data. Classification accuracies typically were within 3% (absolute units) of measured cover values. Video imaging can provide an intuitive understanding of the fraction of the soil covered by residue