Evaluation of measured and simulated cotton water use and yield under full and deficit irrigation

Authors: IBRAGIMOV, NAZAR - Uzbekistan Cotton Research Institute; Evett, Steven - Steve; Schwartz, Robert; Baumhardt, Roland - Louis

Submitted to: National Cotton Council Beltwide Cotton Conference
Publication Type: Proceedings
Publication Acceptance Date: 12/30/2014
Publication Date: 1/5/2015
Citation: Ibragimov, N., Evett, S.R., Schwartz, R.C., Baumhardt, R.L. 2015. Evaluation of measured and simulated cotton water use and yield under full and deficit irrigation. Beltwide Cotton Conference, San Antonio, Jan.5-7, 2015, 956-961:CDROM

Interpretive Summary: Cotton is an important crop in the Texas Panhandle High Plains. However, limited irrigation water availability can make it difficult to produce a profitable crop. Computer models of crop growth, water use and yield can help in deciding how to best manage short irrigation water, but only if the models are accurate. Scientists at the USDA-ARS Conservation & Production Research Laboratory tested a new cotton model using two years of cotton water use and yield data collected using accurate weighing lysimeters. This AquaCrop model was developed to investigate different deficit irrigation strategies. The model was calibrated using data from one year for fully irrigated cotton, then tested against data from two years of deficit irrigation and one year of full irrigation. The model overestimated losses due to evaporation from the soil surface. This could be corrected only by changing model parameters to unrealistic values. Some model functions did not work as indicated by the documentation. Using unrealistic parameter values, the model was able to estimate cotton yields to within 12 percent. It overestimated for full irrigation and underestimated for deficit irrigation. Overall, the model cannot be recommended for developing deficit irrigation practices until the computer code is changed to work correctly and to function correctly using physically realistic parameter values

Technical Abstract: The AquaCrop model simulates crop growth, water use, yield, and water use efficiency of several crops including cotton. The model is intended to be useful for irrigation planning and management, and it attempts to balance simplicity and accuracy so that it can be applied in locations where weather and soil data are limited. However, past research suggests that AquaCrop simulations are less robust when crops are irrigated at deficit levels and consequently under water stress. Our objective was to evaluate the accuracy with which AquaCrop simulates soil water balance, soil water content, above ground biomass and yield of irrigated cotton (Gossypium hirsutum) at two irrigation levels. Soil water use, biomass, and lint-seed yield of cotton in the Texas High Plains, USA, were evaluated during the 2000 to 2002 growing seasons under full and deficit sprinkler irrigation. The fields were equipped with large weighing lysimeters to evaluate soil water use. The capability of the model to accurately predict soil water use within the profile and throughout the growing season as well as the conversion of transpiration to aboveground biomass and seed lint yield production tested. The model overestimated losses due to evaporation from the soil surface. This could be corrected only by changing model parameters to unrealistic values. Some model functions did not work as indicated by the documentation. Using unrealistic parameter values, the model was made to estimate cotton yields to within 12 percent, but it overestimated for full irrigation and underestimated for deficit irrigation. Overall, the model cannot be recommended for developing deficit irrigation practices until the computer code is changed to work correctly and to function correctly using physically realistic parameter values.