|Mcmurtrey Iii, James|
Submitted to: Intnl Conference On Geospatial Information In Agriculture And Forestry
Publication Type: Proceedings
Publication Acceptance Date: 8/15/2001
Publication Date: 11/5/2001
Citation: Interpretive Summary: A new spectrally derived index and method for the site specific management of nitrogen needs in field corn is suggested. The technique requires at least one aerial acquisition of hyperspectral or four narrow bands of spectral image data. The spectral data should be four meter or less ground resolution of the entire field area at or near the time tasseling of a field of corn that has been planted as a mono-culture. Specific spectral data in four narrow areas of the spectrum centered near 550, 630, 670, and 700 nm is required. Bare field areas kept free of green vegetation and areas were no nitrogen has been applied are needed for image data processing controls with in the field. In general the index is designed to track the relative changes in the concentration of chlorophyll a to chlorophyll b in site specific areas of the corn canopy. Site specific patterns of this spectral corn canopy attribute are acquired in one year and are used to guide the next years nitrogen fertilizer application rates across site specific areas of the field.
Technical Abstract: Development of a new index for detecting changes in the primary plant pigments Chlorophyll a and b for nitrogen management in field corn in comparison to previously suggested hyperspectral indices were the objectives of this study. A large field plot experiment in a major U.S. Corn Production Area, near Shelton, Nebraska was used for the testing. Plant leaf samples were taken for pigment extractions and N tissue analysi during the growing season. By a mid-vegetative stage, the trends in the concentrations tended to indicate a ranking consistent with the expected changes in pigment concentration according to nitrogen applied. In later vegetation statistically significant concentration trends developed in Chlorophyll a, b, a/b, total chlorophyll and N tissue analysis for the limited number of plant samples that were able to be tested. Hyperspectral ratios or indices reported to predict accumulation of the plant pigments were compared. A new spectral index, a Modified Chlorophyll Absorption in Reflectance Index for chlorophyll a - chlorophyll b (MCARI a - b) for tracking differences of chlorophyll a minus chlorophyll b gave significant differences between spectra attributes of over-fertilizer as well as under-fertilized nitrogen treatments in the corn canopies. The data inferred that the new index will be useful for determining nitrogen needs within agricultural fields of corn. The MCARI a - b index technique is proposed for further studies and suggestions are provided for methodology to recommend N rate in different site specific areas (pixels) of corn fields that have been planted as a mono culture.