Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/19/2005
Publication Date: 5/1/2005
Citation: Daughtry, C.S., Hunt, E.R., Doraiswamy, P.C., McMurtrey, J.E. 2005. Remote sensing the spatial distribution of plant litter. Agronomy Journal. 97:684-871. Interpretive Summary: Crop residues on the soil surface play significant roles in the surface energy balance, net primary productivity, nutrient cycling, and carbon sequestration. Conservation tillage maintains crop residues on the soil surface to control soil erosion. Long-term use of conservation tillage practices can also lead to increased soil organic carbon, improved soil structure, and increased aggregation compared with intensively-tilled soils. Rapid and accurate methods are needed to quantify residue cover and tillage intensity at local and regional scales. We evaluated several spectral indices for measuring crop residue cover using ground-based and airborne hyperspectral data to categorize soil tillage intensity in agricultural fields at the Beltsville Agricultural Research Center near Beltsville, Maryland. The reflectance spectra of dry crop residues displayed a broad absorption feature near 2100 nm associated with cellulose and lignin. Crop residue cover was linearly related to the Cellulose Absorption Index (CAI), which is the relative depth of the 2100 nm absorption feature. Tillage intensity classes based on crop residue cover were correctly identified in 85% of the agricultural fields in the scene. Regional surveys of soil management practices that affect soil conservation and soil carbon dynamics appear feasible using advanced remote sensing systems.
Technical Abstract: Management of plant litter or crop residues in agricultural fields is an important consideration for reducing soil erosion and increasing soil organic carbon. Current methods of quantifying crop residue cover are inadequate for characterizing the spatial variability of residue cover within fields and across large regions. Our objectives were to evaluate several spectral indices for measuring crop residue cover using ground-based and airborne hyperspectral data and to categorize aoil tillage intensity in agricultural fields based on crop residue cover. Reflectance spectra of mixtures of crop residues, green vegetation, and soil were acquired over the 400-2400 nm wavelength region. High altitude AVIRIS data were also acquired near Beltsville, MD in May 2000. The spectra of dry crop residues displayed broad absorption features near 2100 nm and 2300 nm associated with cellulose and lignin, that were absent in spectra of soils and green vegetation. Crop residue cover was linearly related to the Cellulose Absorption Index (CAI), which was defined as the relative depth of the 2100 nm absorption feature. Green vegetation cover in the scene attenuated CAI, but was linearly related to the Normalized Difference Vegetation Index (NDVI). Various spectral indices for crop residue were evaluated by simulating the relatively broad spectral bands of the Landsat TM and ASTER sensors. The spectral indices based on the AVIRIS or ASTER bands were linearly related to crop residue cover and correctly classified tillage intensity classes in 73 of 86 agricultural fields (85% correct). Regional surveys of soil management practices that affect soil conservation and soil carbon dynamics may be feasible using advanced multispectral or hyperspectral imaging systems.