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Improving irrigation efficiencies through variable rate technology

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Earl Vories, agricultural engineer, USDA-ARS, is part of a team developing variable rate irrigation technology on center pivot irrigation systems.
Creating prescriptions for center pivot irrigation systems

Producers using weather-based methods to schedule irrigation rely on estimates of water lost from plant evapotranspiration (ET) and the amount of rain and irrigation water that make it to the plant root zone. One such system is the University of Missouri Extension Crop Water Use application which tracks soil moisture in fields.

This method optimizes yield potential and water conservation. “What this system doesn’t do however, is take into consideration the variability of soils across a field,” says Dr. Earl Vories, agricultural engineer, USDA-ARS, speaking to those on his precision irrigation tour stop during the 58th annual Fisher Delta Research Center field day in Portageville, Mo.

“It’s that variability that diminishes the effectiveness and efficiency of conventional irrigation management, especially on highly variable soils. If a producer is using variable rate to apply nutrients, seeds, and/or chemicals on highly variable soils, the benefits of that variable rate technology could be masked by the delivery of inappropriate amounts of water.”

Many growers use Veris rigs to measure their soil’s apparent electrical conductivity (EC). In low salinity soils, as apparent EC levels increase, soils have a higher clay content. Lower EC levels indicate sandier soils, which are more likely to encounter drought stress.

“Soil texture will impact irrigation scheduling, but a field’s soil texture is not likely to change; therefore, to increase the efficiency of irrigation scheduling, we need to supplement that soil information with a measure of crop stress, soil moisture, and other aspects of the growing environment that may change during the season,” says Vories.

Sensor-based technologies

A team of USDA-ARS scientists in Bushland, Texas, have patented a system that can develop prescriptions and control Variable Rate Irrigation systems like the ones at the Fischer Delta Research Center. “It’s called an Irrigation Scheduling Supervisory Control and Data Acquisition (ISSCADA) system,” says Vories.

Through a network of integrated sensors, including infrared thermometer (IRT) sensors that measure crop canopy temperature, the ISSCADA helps determine a crop’s water needs and provides spatially variable water rate recommendations.

“The IRT sensors accumulate that temperature-based data and calculates a crop’s stress index,” says Vories. “We are also utilizing sensors that provide normalized difference vegetation index (NDVI) data which we can use to design variable rate irrigation (VRI) prescriptions.”

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Red valves attached to each center pivot sprinkler line turn on and off water flow allowing variable rate irrigation to occur.

The researchers know clouds and other environmental factors may influence those canopy temperature readings, so they have another network of soil-based sensors to monitor the water content in the ground. “It provides us with a second opinion of sorts,” says Vories.

Vories and the other cooperating researchers are evaluating several data-gathering systems so producers will have a choice of options from which to choose. “No two farming operations are identical, and we want growers to be able to tailor a system that best fits their needs,” says Vories.

The USDA-ARS currently has a cooperative research and development agreement with Valmont, a partner who is evaluating the ISSCADA system for potential commercialization.

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