Cotton Canopy Reflectance at Landscape Scale as Affected by Nitrogen Fertilization
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Multispectral reflectance of crop canopies has potential as an in-season indicator of N status in cotton (Gossypium hirsutum L.). The objectives of this study were to correlate leaf N with reflectance at 16 wavebands from 450 to 1700 nm and to assess the effect of N fertilization on vegetative ratio indices using two bands of reflectance. We also compared regressions of leaf N on ratio indices with partial least squares (PLS) regression using reflectance at 16 wavebands. Reflectance was measured at 50 cm above the canopy at 135 points in a 14-ha field of irrigated cotton at early squaring in the Texas High Plains in 2002 and at an 80-cm height in 2003 and 2004. Leaf N had weak, negative correlation with green reflectance in all 3 yr. Normalized difference vegetative indices (NDVIs) using red (670 nm) or green (550 nm) reflectance were significantly greater in N-fertilized plots than zero-N plots in 2 of 3 yr. However, the NDVIs related poorly or not at all with leaf N, biomass, and lint yield. Leaf N was estimated by PLS regression with three factors having R 2 of 0.64 in 2002 and 2004 when an N fertilizer response was observed. In 2003, there was no added N effect, and the R2 for PLS regression of leaf N was 0.41. The poor correlation between NDVIs and leaf N was not expected, and these results suggest that use of NDVIs to determine need of in-season N may be most successful using well-fertilized areas and the sufficiency index approach. American Society of Agronomy.
author list (cited authors)
Bronson, K. F., Booker, J. D., Keeling, J. W., Boman, R. K., Wheeler, T. A., Lascano, R. J., & Nichols, R. L.
complete list of authors
Bronson, Kevin F||Booker, JD||Keeling, J Wayne||Boman, Randy K||Wheeler, Terry A||Lascano, Robert J||Nichols, Robert L