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Spectral measurements were made over cotton which had received five
different preplant nitrogen fertilization rates for the third consecutive year
in 2000. Half of the plots received only rain (WL) and the other half were
fully irrigated to replace potential evapotranspiration (WH).Multispectral
reflectance measurements were made to determine when seedling
emergence could first be detected, and later in the season to detect plant
size differences due to water and nitrogen treatments, and to estimate other
crop agronomic factors. Spectral reflectance values were calculated for the
blue(0.45 -0.52 µ), green (0.52 -0.60 µ), red (0.63 -0.69 µ), and near
infrared (0.76 -0.90 µ) wavelengths and related to various plant
characteristics. The presence of emerged seedlings was detected seven days
after planting (one day after initial emergence) on DOY 143 by spectral
reflectance in the red wavelength and by the normalized difference
vegetation index (NDVI). At this time leaf area in the target areas averaged Between first square and peak bloom, NDVI was not sensitive to nitrogen fertilization level. Leaf area index differences between water levels was positively related to NDVI. Plant height was also positively related to NDVI across sampling dates, but within sample dates only at peak bloom. Similarly NDVI was negatively related to leaf nitrogen content in the WH treatment across dates. NDVI values separated plots into two progressively distinct groups as sampling proceeded from first square to peak bloom and these groups coincided with the WL and WH treatments. NDVI at peak bloom was significantly correlated with lint yield of the WH treatment, but not the WL treatment yields which were low and showed little variation. |
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©National Cotton Council, Memphis TN |
Document last modified XXXXXX, XXX XX 2001
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