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Narrow-Waveband Reflectance Ratios for Remote Estimation of Nitrogen Status in Cotton

^a USDA-Agricultural Research Service, Crop Science Research Laboratory, P.O. Box 5367, Mississippi State, MS 39762
^b Texas A&M Research and Extension Center, 1509 Aggie Dr., Beaumont, TX 77713
^c Plant and Soil Science Dep., Box 9555, Mississippi State, MS 39762

View larger version (29K): [in a new window]   Fig. 1. Evolution of (a) total chlorophyll, (b) carotenoids, and (c) nitrogen in uppermost fully expanded leaves of cotton, n = 69. Vertical arrows indicate sampling dates on which both leaf and canopy reflectance were measured (n = 22); these data were subsequently used in correlation analysis (see Fig. 3, 4, 5, and 6). Leaf and canopy reflectance measurements were obtained only once, on 23 August, in the 0% of control N at boll-filling onward treatment.

View larger version (25K): [in a new window]   Fig. 2. Relationship between net CO2 exchange and leaf chlorophyll concentration in uppermost leaves of cotton grown under N-limiting conditions. Values represent single observations obtained from five leaves in each treatment and sampling date.

View larger version (23K): [in a new window]   Fig. 3. Coefficients of determination (r2) for the linear relationship between (a) leaf reflectance and leaf chlorophyll concentration, (b) reflectance at 755 nm divided by reflectance at wavelength indicated by the horizontal axis, and (c) reflectance at 705 nm divided by each wavelength. All plot means of spectral reflectance and chlorophyll collected during the two-month study (n = 60) were included in correlation analyses.

View larger version (21K): [in a new window]   Fig. 4. Coefficients of determination (r2) for the linear relationship between (a) leaf reflectance and total leaf nitrogen concentration, (b) reflectance at 755 nm divided by reflectance at wavelength indicated by the horizontal axis, and (c) reflectance at 700 nm divided by each wavelength. All plot means of spectral reflectance and chlorophyll collected during the two-month study (n = 60) were included in the correlation analyses.

View larger version (21K): [in a new window]   Fig. 5. Coefficients of determination (r2) for the linear relationship between (a) canopy reflectance and total leaf chlorophyll concentration, (b) reflectance at 700 nm divided by reflectance at wavelength indicated by the horizontal axis, and (c) reflectance at 415 nm divided by reflectance at each wavelength. All plot means of spectral reflectance and chlorophyll collected during the two-month study (n = 22) were included in correlation analyses.

View larger version (21K): [in a new window]   Fig. 6. Coefficients of determination (r2) for the linear relationship between (a) canopy reflectance and total leaf nitrogen, (b) reflectance at 415 nm divided by reflectance at wavelength indicated by the horizontal axis, and (c) reflectance at 710 nm divided by reflectance at each wavelength. All plot means of spectral reflectance and chlorophyll collected during the two-month study (n = 22) were included in the correlation analyses.

View larger version (31K): [in a new window]   Fig. 7. Relationships between leaf nitrogen (N) concentration and (a–f) various single-waveband canopy reflectance ratios across different N treatments and sampling dates. Best-fit regression lines are represented by solid lines, with the exception of R755/R700 for which a dashed line is used to represent the regression function when leaf N values > 40 g kg-1 are excluded (df = 17, r2 = 0.82**). **Significant at P < 0.01; otherwise, not significant (ns).