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Modeling Water-Stressed Cotton Growth Using Within-Season Remote Sensing Data

^a Texas A&M Univ., Texas Agric. Exp. Stn. at Uvalde, 1619 Garner Field Rd., Uvalde, TX 78801-6205
^b Texas Tech Univ. Plant and Soil Science, 3810 4th St., Lubbock, TX 79415
^c USDA-ARS Cropping Systems Research Lab., 3810 4th St., Lubbock, TX 79415

View larger version (19K): [in a new window]   Fig. 1. The soil line determined from the linear relationship between near-infrared (NIR) and red reflectance of bare soils of 2002, 2003, and 2004 data (n = 432).

View larger version (22K): [in a new window]   Fig. 2. Diagrammatic representation of the model that shows daily cotton growth processes and the within-season calibration (modified from Maas, 1993a and 1993b). Measured and simulated growths refer to measured and simulated leaf area index or vegetation indices. AGDM, above-ground dry mass; GDD, growing degree days; LAI, leaf area index; PAR, photosynthetically active radiation.

View larger version (13K): [in a new window]   Fig. 3. An example of simulated leaf area index (LAI) passing through measured LAI values. The dotted lines (E1 to E4) represent the errors between simulated and measured values of LAI.

View larger version (27K): [in a new window]   Fig. 4. Changes of average reflectance values for each waveband during crop growing season in 2002, 2003, and 2004. Measurements were made after day of year (DOY) 206 in 2002, and not all measurement dates are shown in 3 yr. Cotton was planted on DOY 133 in 2002 and 2003 and on DOY 134 in 2004.

View larger version (33K): [in a new window]   Fig. 5. Changes of reflectance for each waveband at the seasonal average (left) of measured data and at close to maximum leaf area index (right) as a function of different irrigation levels in 2002, 2003, and 2004. Vertical bars represent standard errors on the data points (for each treatment, n = 49 in 2002, n = 36 in 2003 and in 2004). Cotton was planted on day of year (DOY) 133 in 2002 and 2003 and on DOY 134 in 2004. LAI, leaf area index.

View larger version (40K): [in a new window]   Fig. 6. Simulated vs. measured VI and LAI for different irrigation levels in 2002, 2003, and 2004. The solid diagonal line represents the ratio 1:1. The VI are normalized difference vegetation index (NDVI), re-normalized difference vegetation index (RDVI), modified triangular vegetation index (MTVI), optimized soil-adjusted vegetation index (OSAVI), and perpendicular vegetation index (PVI).

View larger version (33K): [in a new window]   Fig. 7. Simulated vs. measured average lint yields for 3 yr and four irrigation levels data using five different vegetation indices (VI) and leaf area index (LAI). Vertical bars represent variation of the mean, and horizontal bars represent SE for observed values. The solid diagonal line represents the ratio 1:1. The VI are normalized difference vegetation index (NDVI), re-normalized difference vegetation index (RDVI), modified triangular vegetation index (MTVI), optimized soil-adjusted vegetation index (OSAVI), and perpendicular vegetation index (PVI).

View larger version (40K): [in a new window]   Fig. 8. Simulated vs. measured VI and LAI for different irrigation depths in 2005. The VI are normalized difference vegetation index (NDVI), re-normalized difference vegetation index (RDVI), modified triangular vegetation index (MTVI), optimized soil-adjusted vegetation index (OSAVI), and perpendicular vegetation index (PVI).

View larger version (35K): [in a new window]   Fig. 9. Simulated vs. measured lint yields for four irrigation treatments using five different vegetation indices (VI) and leaf area index (LAI) in 2005. The solid diagonal line represents the ratio 1:1. The VI are normalized difference vegetation index (NDVI), re-normalized difference vegetation index (RDVI), modified triangular vegetation index (MTVI), optimized soil-adjusted vegetation index (OSAVI), and perpendicular vegetation index (PVI).