ESTIMATING CROP RESIDUE COVER BY BLUE 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. C urrent methods for quantifying crop residue cover use tedious manual s ampling methods or visual comparisons with photographs. There is a nee d for new methods to quantify residue cover that are rapid, accurate, and objective. Scenes with known amounts of crop residue were illumina ted in the lab with long-wave ultraviolet (UV) radiation and fluoresce nce images were measured and recorded with a video camera equipped wit h a mico-channel-plate image intensifier and fitted with a 453-488 nm bandpass filter. Six agricultural soils were used as backgrounds for t he weathered soybean residue. Residue cover was determined from the pr oportion of the pixels in the image with fluorescence values greater t han a threshold. Soil pixels gave the lowest fluorescence or brightnes s responses in the images and the residues the highest, so that bright ness values of the scene spanned nearly the full range of the 8-bit vi deo data. The images were classified in brightness categories that rel ated to within 2% (absolute units) of measured residue cover regardles s of the soil type or moisture condition (dry vs. wet). Therefore, flu orescence images can be used to provide percent residue cover in the l ab, but portable equipment and procedures for use in the field still n eed to be developed. (C) Elsevier Science Inc., 1997.