Irrigation Farming Gets Pay Off From Soil Moisture Monitoring

Irrigation Farming Gets Pay Off From Soil Moisture Monitoring

Irrigation scheduling can be designed around soil-moisture monitors of various types

Nithya Rajan , Texas AgriLife Research agronomist, has completed a year of data analysis and demonstrating different tools to aid producers with irrigation efficiency on the Rolling Plains of Texas. The Vernon-based researcher says 2011 was a good year to test the tools because of no rain.

"Most of the farmers in this region don't use irrigation scheduling tools, so they might not apply the right amount of water," Rajan says, noting there are pumping costs and water to be saved.

While Rajan says irrigation scheduling tools are a key to efficient irrigation, there has not been a demonstration project in the past showing which tool might fit the needs of a producer best on the Rolling Plains.

KEEPING IN TOUCH: Nithya Rajan looks at the SmartField sensor that is part of her study on irrigation scheduling tools at Vernon, Texas.

Her two-year project, which began in 2011 on a sub-surface irrigated cotton crop, is comparing four different irrigation scheduling tools as a guide on when - and how much - to irrigate.

SmartField sensor

The SmartField sensor being used in the study is based on crop canopy temperature, Rajan says. When the crop canopy temperature gets above 80 degrees, the crop is assumed to be in stress and needs irrigation within about six hours.

But the problem in 2011 was the extreme heat.

"The air temperature is so high that even though the plants are transpiring and cooling down, the crop canopy might be showing 80 degrees even though irrigation is being applied," she notes.

In that case, the producer may have to use some of their own judgment in applying irrigation, or use the SmartField sensors in combination with other tools, Rajan says.

Tensiometers

Tensiometers cost about $70 to $100 per unit and basically consist of a sensor placed into the ground. The sensor must be filled with water and an air-tight cap is placed on it. Then tensiometer has a ceramic tip that contacts the soil, and when the soil gets dry, it draws water of the device, which shows up as an increased soil tension.

"This tension in the sensor can be read on a meter which is part of the tensiometer," Rajan says. "When the meter reaches about 50 (centibar), it is a common practice to irrigate and bring the pressure back to about 10-20."

Tensiometers are easy to use and easy to install, she says. Generally, several are installed in a group in the field, and the producer must refill water in the sensor at least once a week.

Electronic sensors

Electronic soil-moisture sensors indicate the amount of water held in the soil, with the goal being to irrigate just enough to keep the soil moisture close to 75% of field capacity, Rajan says.

The soil-moisture sensors require some simple calculations on the producer's part to determine when and how much to water.

 As a crop grows the rooting depth changes and must be taken into account in the calculations.

The soil-moisture sensors with a digital readout cost about $700 to $800, Rajan says.

Potential evapotranspiration

PET

The final method - potential evapotranspiration - uses data from weather observing stations. These include the High Plains Potential Evapotranspiration Network, operated by AgriLife Research in the Panhandle, and the West Texas Mesonet, operated by Texas Tech University in the West Texas region. The West Texas Mesonet has stations at Odell, Haskell, Knox City, Goodlett and Seymour in the Rolling Plains region.

This tool is based on using the potential rate of evapotranspiration and the growth stage of the crop to determine how much moisture should be applied to replace what is being lost by both plant and soil evaporation.

The two-year study is being partially funded by the Texas Water Development Board. Project collaborators are Srinivasulu Ale, hydrologist, and Paul DeLaune, soil scientist, both with AgriLife Research, Vernon.

For RESULTS click on the Cropping Systems link under Center Programs and then on Cropping Systems Research.

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