As part of the effort to examine possible causes for the cotton (Gossypium hirsutum L.) yield decline problem, the cotton crop model GOSSYM was used to analyze long-term effects of weather on cotton yield. Weather, soil, and cultural input data taken at five locations for over 25 years were acquired for this study. Simulations were completed for crops at the cotton breeder sites at Stoneville, MS; Phoenix, AZ; Fresno, CA; Lubbock, TX; College Station, TX; and Florence, SC. With some exceptions, essentially the same plots were used at these sites with the same cultivars over the 25-year period.

For each location a full-season simulation was made using the cultural practice inputs for that crop in each year during the 25-year period. The weather factors were analyzed for each location to determine If there were a statistically significant trend which could account for the yield decline. The results of these tests were negative for solar radiation, average air temperature, maximum air temperature, minimum air temperature, and rainfall/irrigation amounts. The predicted yields from the simulations were analyzed using the Cox-Stuart procedure. This analysis showed that the weather factors per Be did not account for the yield decline for each location.