Effects of Cultural Practices on Agronomic and Reflectance Characteristics of Soybean Canopies
1982
Kollenkark, J. C. | Daughtry, C. S. T. | Bauer, M. E. | Housley, T. L.
Understanding the relationship between the reflectance measured and the various cultural practices used in today's soybean production is key for further development and use of remote sensing as a tool for crop monitoring. Field experiments were conducted at the Purdue Agronomy Farm in West Lafayette, Ind. in 1978 and 1979 to study the reflectance factor (RF) of soybean (Glycine max L. Merr.) canopies as affected by differences in row width, population, planting date, cultivar, and soil type (Typic Argiaquoll and Typic Hapludulf). Reflectance factor (RF) data were acquired with a Landsat-band radiometer (Exotech 100), which is a four band radiometer with a 15-degree field of view that measures radiance in the following wavelength regions: 0.5–0.6, 0.6–0.7, 0.7–0.8, and 0.8–1.1 µ. Agronomic measurements included plant height, leaf area index, development stage, total fresh and dry biomass, and percent soil cover. Row width, planting date, and cultivar influenced the percent soil cover, leaf area index, biomass, and development stage of the soybean canopies. Changes in these agronomic variables were manifested in the canopy reflectance. Soil color and moisture were important factors influencing RF in single Landsat bands; however, the near infrared/ red reflectance ratio and the greenness transformation were less sensitive than the single bands to changes in soil background. Variations in spectral responses are strongly associated with planting date during early to mid-season, with the row width during mid-season to near maturity, and with cultivar at maturity. This information should be useful in applications of remote sensing for identifying crops and estimating crop condition and yields.
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