|Yves Le Gal, Pierre|
Submitted to: International Evapotranspiration Irrigation Scheduling Conference
Publication Type: Proceedings
Publication Acceptance Date: 11/6/1996
Publication Date: N/A
Interpretive Summary: Crop water needs is only one factor affecting a farmer's decision of when to irrigate a crop. Other factors such as soil variability within a field, scheduling of tillage operations, flexibility of the water supply, physical farm layout, and labor scheduling, also determine when to apply water to a field. A study is being conducted to understand better how these additional factors influence the farmer's irrigation scheduling decisions. The objective is to identify formal and informal rules followed by the farmer to achieve his or her irrigation management goals. The results of this study will help other farmers identify successful irrigation management strategies currently in use. This type of information can also be useful to water district managers interested in developing water delivery procedures that better meet farmers' needs, and to researchers working in the development of irrigation scheduling tools that are more practical than existing tools. Initial results clearly show that the decision of when to irrigate an individual field involves a compromise between crop water needs and farm management constraints.
Technical Abstract: Irrigation scheduling is a complex decision making process as crop water needs vary during the growing season and among locations within a farm. Practical considerations influence also when water is applied to a field. Understanding how these constraints interact and affect farmers' decisions can help us develop strategies for improving their irrigation management. This can help also water district managers develop water delivery rules that better meet farmers' needs, and guide researchers in the development of irrigation scheduling tools that are more practical than existing ones. The irrigation scheduling process is being examined through a case study in Arizona. The concept of action model, developed to study agricultural labor management, is being used to identify and model the set of rules followed by a farmer to achieve predefined irrigation management goals. The study involves a grower with extensive and detailed records of his irrigation practices. Irrigation scheduling rules were identified from grower interview data and from grower-collected data for the 1993 irrigation season. A model was then developed to simulate the farmer's irrigation schedule as a function of crops, weather, and management constraints. The model was validated by comparing simulated with actual 1994 irrigation data. Results show that, besides crop water needs, field level (e.g., soil diversity), farm-level (e.g., labor scheduling), and even personal attitudes, impact irrigation practices.