Using Crop Simulation Models as a Tool for Abiotic Stress Characterization of Cotton.

Drought and temperature stress are important variables that can affect crop yield. However; studies comparing the magnitude, duration and timing of crop stress for different seasons and locations and its impact on field crops have been limited. Process-based crop simulation models can be used to predict growth, development, and yield for many different crops. The objectives of this study were 1) to characterize the conditions related to drought and temperature stress for specific developmental phases of a set of cotton trials that were conducted in a range of environments; 2) to determine the impact of water stress on yield by comparing simulating yields under water stress conditions vs. yield under non-limiting water conditions and 3) to determine the reduction in yield per unit of simulated water stress index during the growing season and for the critical month around flowering. Cotton trials were conducted across USA during growing season of 2008 and 2009. The data available for these trials included crop management practices, local soil series, daily weather data, crop phenology and yield. The CSM-CROPGRO-Cotton model was used to simulate cotton growth and development. Model calibrations were performed for phenology and yield. Model outputs were analyzed with emphasis on crop water stress for the period around flowering. Drought stress is one of the outputs of the models, and it is simulated on a daily base using the ratio between daily potential plant water uptake and the potential evapotranspiration. The simulations were analyzed with emphasis on the cumulative drought stress for the entire growing season as well as for a specific period during the growing season. This specific period ranged from 10 days prior to flowering to 30 days after flowering, which includes the most critical period for drought sensitivity around flowering. “Day temperature stress” was calculated using maximum daily temperatures in a linear equation from 0 to 1, corresponding to 30 and 42^oC, respectively. 

The study allowed us to identify locations and planting dates that were under temperature and water stress around flowering of cotton using a modeling approach. The analysis combining water and temperature stress during the growing season can help with understanding the impact on crop performance and final yield.