Submitted to: Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/22/2016
Publication Date: 8/31/2016
Citation: Mahan, J.R., Lascano, R.J. 2016. Irrigation analysis based on long-term weather data. Agriculture. 6(3):42.
Interpretive Summary: Irrigation management provides a tool for farmers to prevent the wasteful application of water. A useful irrigation management scheme will assist the irrigator in decisions relating to the timing of irrigation and the amount of water to apply. Evapotranspiration (ET)-based irrigation scheduling is widely used worldwide. The Texas High Plains region of the US had one of the first modern ET networks for general use. In this study we carried out an historical analysis to determine how the declining water reserves in the region has affected the usefulness of the ET network. Our results demonstrate that at current and future irrigation levels the usefulness of ET values for irrigation has declined in the region. Adoption of the methodology has suffered as a result.
Technical Abstract: Irrigation-management is based upon delivery of water to a crop in the correct amount and time, and the crop’s water need is determined by calculating evapotranspiration (ET) using weather data. In 1994 an ET-network was established in the Texas High Plains to manage irrigation on a regional scale. Though producers used the ET-network by 2010 public access was discontinued. Why did producers allow a valuable irrigation-management tool to be eliminated? Our objective was to analyze the effect of declining well capacities on the usefulness of cotton ET (ETc) for irrigation. Thirty years (1975 – 2004) of daily ETc data were used to compare irrigation-demand vs. irrigation-responses at four locations and analyzed for multiple years and range of well capacities on three irrigation-intervals. Results indicated that when well capacities declined to the point that over-irrigation was not possible, the lower well capacities reduced the value of ETc in terms of the number of irrigations and total amount of water applied. At well capacities < 1514 L min-1 the fraction of irrigations for which ETc information was used to determine the irrigation amount was < 35% across years and irrigation intervals. The value of an ETc-based irrigation may fall into disuse when irrigation-water supplies decline.