Precision irrigation

Authors: Vories, Earl

Submitted to: University of Missouri Agricultural Experiment Station Publication
Publication Type: Abstract Only
Publication Acceptance Date: 8/2/2019
Publication Date: 8/31/2019
Citation: Vories, E.D. 2019. Precision irrigation [abstract]. University of Missouri Agricultural Experiment Station Publication. p. 20-21.

Interpretive Summary:

Technical Abstract: Weather-based methods schedule irrigation by estimating the amount of water lost from plant evapotranspiration (ET) and the amounts of effective rainfall and irrigation water entering into the plant root zone. One such system is The University of Missouri Extension Crop Water Use application, which helps farmers improve irrigation management by tracking soil moisture in fields for optimum yields and water conservation. However, soil textural variability within many irrigated fields diminishes the effectiveness of conventional irrigation management. Scheduling methods that assume uniform soil conditions may produce less than satisfactory results on highly variable soils, and benefits of variable-rate application of agrochemicals, seeds, and nutrients can be masked by applying inappropriate amounts of water. Precision irrigation, or variable rate irrigation (VRI) provides the opportunity to address some of these problems. Looking at a map of apparent electrical conductivity (ECa) measured on one of our research fields, as the values increase, the soil has a higher clay content. In this case, the higher-EC areas are the more productive parts of the field and the lowest-EC portions are sandier and more likely to encounter drought stress. The variable soil texture presents challenges for traditional irrigation management on this field, which was the first field at the Fisher Delta Research Center equipped with VRI. We know that soil texture will impact the irrigation schedule, but we don’t expect soil texture to change. Therefore, we need to supplement the soil information with measures of crop stress, soil moisture, or something that changes during the growing season. The USDA-ARS team in Bushland, TX, patented an Irrigation Scheduling Supervisory Control And Data Acquisition (ISSCADA) system that can develop prescriptions and control VRI systems. With integrated sensor networks, the ISSCADA system detects variable crop water needs and provides spatially variable recommendations for watering rates. A network of infrared thermometer (IRT) sensors monitors the crop canopy temperature and calculates a crop stress index from them. A second network of soil moisture sensors monitors the soil water content in the field. The canopy temperature measurements can be influenced by clouds and other factors so the soil moisture serves as a “second opinion” regarding the irrigation recommendation. Combining the data from the two networks, a prescription map is prepared and sent to the center pivot control panel. Other measurements are also being investigated for directing precision irrigation. Sensors on ground equipment, a plane, or an unmanned aerial vehicle (UAV) can measure canopy temperature, normalized difference vegetation index (NDVI) or other factors that can be used to produce VRI prescriptions. The “best” measurement for preparing VRI prescriptions will depend on how variable the soil is and what equipment is available.