Submitted to: Agronomy Journal
Publication Type: Peer reviewed journal
Publication Acceptance Date: 2/8/2009
Publication Date: 4/3/2009
Citation: Evett, S.R., Tolk, J.A. 2009. Introduction: Can water use efficiency be modeled well enough to impact crop management? Agronomy Journal. 101(3):423-425. Interpretive Summary: Computer simulations of crop growth, yield and water use are tools both for water resource managers and policy makers as well as for investigative research. As water resource availability for agriculture becomes limited by competition from industry, municipalities, thermoelectric power generation and environmental uses, improvements in crop water use efficiency (WUE = the yield of grain or fiber per unit of water used) become key to maintaining agricultural production and profitability. Simulation models can be used by planners, water managers, policy makers and producers to investigate different farming system and irrigation application scenarios in order to see which ones yield the largest WUE and thus may produce the same or more yield for less water. Scientists in the USDA-ARS Conservation & Production Research Laboratory, Bushland, Texas, led a scientific meeting on simulation modeling of WUE and organized a special section of the "Agronomy Journal," a primary agricultural science journal in the USA, to report on several simulation models and their effectiveness in estimating WUE under irrigated, deficit irrigation and dryland conditions. Although all the models estimated WUE well under well-watered conditions, not all did a good job under water deficits. The comparison of models will allow scientists to improve the model calculations of WUE for use by irrigators and water managers.
Technical Abstract: Crop water use efficiency (WUE, yield per unit of water use) is key for agricultural production with limited water resources. Policy makers and water resource managers working at all scales need to address the multitudinous scenarios in which cropping systems and amounts, timing, and methods of irrigation and fertilizer applications may be changed in order to improve WUE while meeting yield and harvest quality goals. Experimentation cannot address all scenarios, but accurate simulation models may fill in the gaps. The nine papers in this special section explore how four simulation models were used to simulate yield, water use and WUE of cotton (Gossypium hirsutum L.), maize (Zea mays L.), quinoa (Chenopodium quinoa Willd.) and sunflower (Helianthus annuus L.) in North and South America, Europe and the Middle East. All the models simulated WUE well under well-watered conditions, but tended to misestimate WUE under conditions of water stress, which limits their use for exploration of deficit irrigation scenarios or rain fed or dryland situations with expected soil water deficits. None of the experimental conditions reported involved separate measurements of evaporation (E) and transpiration (T); so there was no opportunity to test the separation of E and T simulated in the newest of the models, AquaCrop. The lack of separate E measurements also limited the authors in exploring reasons why WUE was not simulated well under water stress conditions. Future studies exploring WUE simulation should include E or T measurements so that effects of management methods that reduce E can be studied.