Submitted to: Remote Sensing of Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 30, 2007
Publication Date: N/A
Interpretive Summary: Crop residues on the soil surface decrease soil erosion, increase soil organic matter, and improve soil quality. Thus, management of crop residues is an integral part of many conservation tillage systems. The standard technique for measuring crop residue cover used by the USDA Natural Resources Conservation Service (NRCS) is visual estimation along a line-transect is not well suited for regional assessments. Remote sensing approaches have had mixed success because crop residues and soils are often spectrally similar. An alternative approach is based on detecting a broad absorption feature near 2100 nm that is associated with cellulose and lignin in plants. The relative intensity of this absorption feature was defined as the cellulose absorption index (CAI). Unfortunately, water in crop residues and soil attenuates the CAI and makes assessments of residue cover difficult. A method to assess scene moisture and modify the expected maximum CAI was developed. Additional test are underway to evaluate the technique with satellite data.
Technical Abstract: Crop residues on the soil surface decrease soil erosion and increase soil organic carbon. Thus, management of crop residues is an integral part of many conservation tillage systems. Current methods of measuring residue cover are inadequate for characterizing the spatial variability of residue cover over large fields. Several remote sensing approaches for estimating crop residue cover have been proposed. The objectives of this research were to determine the effects of moisture on the spectral estimates of crop residue and to propose a method to mitigate the effects moisture on estimates of crop residue cover. Spectral reflectance of scenes with varying proportions of crop residues and soils were measured over the 400-2400 nm wavelength region. Additional spectra of scenes with mixtures of crop residues, green vegetation, and soil were also acquired in corn, soybean, and wheat fields with different tillage treatments. Crop residue cover was linearly related to the Cellulose Absorption Index (CAI), which was defined as the relative intensity of an absorption feature near 2100 nm. Moisture in the crop residue in the scene significantly attenuated CAI. A novel method is proposed to assess scene moisture content for modifying the maximum CAI expected for full cover. Regional surveys of soil conservation practices that affect soil carbon dynamics may be feasible using advanced multispectral or hyperspectral imaging systems.