GIS-based irrigation scheduling and on farm water allocation

A GIS-based irrigation scheduling and on farm water allocation program was developed for irrigated crops to assist farmers in maintaining or increasing yields while minimizing water losses and crop stress to water supply shortage. The use of GIS offers a unique approach for agricultural managers to analyze spatial and temporal variability while investigating crop management strategies for water allocation for crops. The system is composed of three modules. The main components of these modules are, an irrigation scheduler, a field water priority setting and an on farm water allocation model. The irrigation scheduler has four sub modules; climatic data, crop growing period, crop information for a specific field, crop coefficient, and evaporation from a wet soil.; The irrigation scheduler uses a traditional soil-water mass balance approach and the concept of management allowable depletion level to trigger the irrigation water needed for a specific crop. The program operates in a real-time mode, using daily crop evapotranspiration and forecasts irrigation water requirements, based on climatic averages. Management allowable depletion levels can be preset for each crop growth stage. Reference evapotranspiration is manually entered into the system. It is calculated by another program using the Penman-Monteith method or can use any other available method.; When water is limited to some crops in the field during a given day, a crop-water priority setting considers the kind of crop grown, rooting depth, stage of growth, crop sensitivity to water stress, crop yield, soil storage capacity and management allowable depletion. Water is allocated to the fields based on this priority setting, water availability and irrigation system constraints. The GIS program will automatically transfer the fields that were left without irrigation to the next day.; The value of this research lies on the integrated analysis of climatic and crop data for the determination and allocation of a limited water supply for crops, that varies in space and time. Also, water demand can vary within a field or from field to field. It provides the ability to process and store a large volume of data in the GIS database layers creating water allocation scenarios and exploring different alternatives in a very efficient manner. The methodology was applied to an agronomic farm of 200 acres located in Larimer County in Colorado.