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Modification of the GRAMI Model for Cotton

USDA-ARS Plant Stress and Water Conserv. Unit, Plant and Soil Sci., Texas Tech Univ., 3810 4th St., Lubbock, TX 79415

View larger version (123K): [in a new window]   Fig. 1. Taking an overhead digital photograph using DyCam in the field (left) and the corresponding digital image (right).

View larger version (24K): [in a new window]   Fig. 2. Daily cotton growth processes used in the model (modified from Maas, 1993a). AGDM, aboveground dry mass; LAI, leaf area index; PAR, photosynthetically active radiation.

View larger version (20K): [in a new window]   Fig. 3. Relationship between leaf area index (LAI) and ground cover (GC) from Field #26, #28, and #33. Open circles are data points before maximum LAI, and filled circles are data points at and after maximum LAI. Horizontal and vertical dotted lines represent average values of LAI and GC at maximum crop canopy.

View larger version (38K): [in a new window]   Fig. 4. (A) Ratio of the daily light energy intercepted by a crop canopy (Q0) versus leaf area index (LAI) and (B) ln(1 – Q0) versus LAI for different light extinction coefficient (k) values from 0.2 to 0.9.

View larger version (20K): [in a new window]   Fig. 5. Diagrammatic representation of how measured crop growth is used to calibrate the model parameters that affect simulated crop growth (after from Maas, 1993b). LAI, leaf area index.

View larger version (21K): [in a new window]   Fig. 6. Simulated leaf area index (LAI) and aboveground dry mass (AGDM) versus measured LAI and AGDM as a function of cumulative growing degree days (GDD) and days after planting (DAP) in Fields #26, #28, and #33. Vertical bars represent error above and below the mean within a 95% confidence interval (±2E).

View larger version (19K): [in a new window]   Fig. 7. Comparison between simulated and measured lint yield. Squares represent average values for each of the three fields. Horizontal bars represent error above and below the mean within a 95% confidence interval (±2E). Vertical bars represent variation of the mean. The solid diagonal line represents the 1:1 ratio.

View larger version (17K): [in a new window]   Fig. 8. Simulated leaf area index (LAI) and aboveground dry mass (AGDM) versus measured LAI and AGDM for the 1999 and 2001 data at Lamesa, TX. Vertical bars represent error above and below the mean within a 95% confidence interval (±2E). DAP, days after planting.

View larger version (20K): [in a new window]   Fig. 9. Simulated leaf area index (LAI) and aboveground dry mass (AGDM) versus measured LAI and AGDM for the 2002 and 2004 data at Lubbock, TX. Vertical bars represent error above and below the mean within a 95% confidence interval (±2E). DAP, days after planting.

View larger version (18K): [in a new window]   Fig. 10. Comparison between simulated and measured lint yield for the 2001 and 1999 data at Lamesa, TX and the 2002 and 2004 data at Lubbock, TX. Horizontal bars represent error above and below the mean within a 95% confidence interval (±2E). Vertical bars represent variation of the mean. The solid diagonal line represents the ratio 1:1.