Fig. 1.

Geographic distributions of (a) the dominant USGS land cover categories in the CWRF model 30-km grids, (b) cotton harvest areas averaged during 1979 to 2005, (c) top soil sand percentage, and (d) irrigated cotton area percentage.


Fig. 2.

Geographic distributions of cotton yield (a) relative mean biases [(] and (b) standard deviation ratios (σso) as simulated by the original GOSSYM, where and σ represent cotton yield means and standard deviations during 1979 to 2005 and the subscripts s and o indicate simulations and observations, respectively.


Fig. 3.

(a) Nitrogen productivity for irrigation ratios of 1.00 (blue), 0.50 (green), and 0.05 (red), and (b) water productivity for residual NO3 values of 440 (blue), 330 (green), and 220 kg ha−1 (red) in the Southwest (California, Arizona, and New Mexico, solid lines), Mid-South (Texas, Oklahoma, Louisiana, Arkansas, Missouri, and Mississippi, dashed lines) and Southeast (Tennessee, Alabama, Florida, Georgia, South Carolina, North Carolina, and Virginia, dotted lines). The black lines are thresholds of 0.75 kg cotton kg−1 NO3 and 100 kg ha−1 for N and water productivity, respectively.


Fig. 4.

Geographic distributions of cotton yield relative mean biases and standard deviation ratios, respectively, for (a) and (f) the control (CNTL), i.e., optimization with water productivity >100 kg ha−1 and N productivity >0.75 kg cotton kg−1 NO3, (b) and (g) irrigation optimization only (OPTI), (c) and (h) fertilization optimization only (OPTN); (d) and (i) optimization without limits on water and N productivity (ULMT); and (e) and (j) no optimization (NOOP).


Fig. 5.

Geographic distributions of (a) initial soil N abundance in the top 2 m of soil (kg ha−1) and (b) the ratio of irrigated water amount to potential evapotranspiration from the control (CNTL) experiment. Both quantities varied across space but remained invariant during 1979 to 2005.


Fig. 6.

Total simulated (black dot) and observed (bar) irrigated water amounts in the U.S. Cotton Belt states in 1984, 1988, 1994, 1998, and 2003.


Fig. 7.

Spatial frequency distributions of all cotton-grid pointwise relative mean biases (black; bottom and left axes), standard deviation ratios (red; top and right axes), and correlation coefficients (green; bottom and left axes) of cotton yields between observations and simulations by the original (dashed lines) and redeveloped (solid lines) GOSSYM.