Purdue Agronomy Farm Corn Nitrogen (791802)
Nitrogen fertilization is one of the primary factors responsible for the
increased yields in the United States in the past 15 years. Four levels
of fertilization, 0, 67, 134, and 202 kg/hectare, providing a range
from distinctly deficient to abundant have been selected from a long
term fertilization experiment. The specific objectives of the
experiment were to (1) determine the threshold of spectral detection
of nitrogen deficiency and (2) determine kind and magnitude of
changes in reflectance and thermal response as a function of level of
nitrogen nutrition. Three replications were used.
Measurements were made at approximately 10 day intervals
throughout the growing season with the Exotech 20C
spectroradiometer over the 0.4 to 2.4 $mu$m wavelength range.
Radiant temperature of the canopy was also measured. In addition to
the standard agronomic data (leaf area index, etc.) leaf nitrogen and
chlorophyll concentrations were determined. Also, leaf reflectance
measurements were made on several dates.