Effects of Management Practices on Reflectance of Spring Wheat Canopies1
- C. S. T. Daughtry,
- M. E. Bauer,
- D. W. Crecelius and
- M. M. Hixson2
Analyses of multispectral measurements from satellites offer the potential to monitor and inventory crop production. The crop canopy is a dynamic entity influenced by many cultural and environmental factors. In order to quantify and understand some of these potential sources of variation in spectral measurements of crops, an experiment was conducted on a Williams loam (fine−loamy, mixed Typic Argiborolls) at the Williston, North Dakota, Agricultural Experiment Station in 1977. The effects of soil moisture, planting date, nitrogen fertilization, and cultivar on reflectance of spring wheat (Triticum aestivum L.) canopies were investigated. Spectral measurements were acquired on eight dates throughout the growing season with a radiometer (Exotech 100 A) in four wavelength bands (0.5 to 0.6, 0.6 to 0.7, 0.7 to 0.8, 0.8 to 1.1 µm) at 3.5 m above the plots. On the days spectral data were taken, measurements of crop maturity stage, leaf area index, biomass, plant height, percent soil cover, and soil moisture were also taken.
In this experiment, planting date and available soil moisture were the primary agronomic factors affecting reflectance of spring wheat canopies from tillering to maturity. Comparisons (R2) of treatments indicated that during seedling and tillering stages, planting date was associated with 36 and 85% of variation in red (0.6 to 0.7 µm) and near infrared (0.8 to 1.1 µm) reflectances, respectively. As the wheat headed and matured, less variation in reflectance was associated with planting date and more with available soil moisture. By mid July soil moisture accounted for 73 and 69% of the variation in reflectance in red and near infrared bands, respectively. Differences in spectral reflectance among treatments were attributed to changes in leaf area index (LAI), biomass, and percent soil cover. Cultivar and N fertilization rate had little association with the variation in reflectance of these canopies. Agronomic practices resulting in differences in LAI, biomass, and percent soil cover potentially can be monitored by remote sensing and this information may be useful in estimating crop production.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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