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Many sensors come with two or three depths to measure moisture. Moisture sensors generally default to an average of the sensor's readings at different depths to determine an irrigation trigger.

Brad Haire, Executive Editor

May 19, 2020

3 Min Read
Brad Haire

Soil moisture sensors provide valuable insight for a grower to know when to trigger irrigation. But early in the season, and even throughout the season, weighing the value of a sensor's different depths can add precision to that decision and save water and money.

Growers know cotton and peanut are resilient and may not need additional irrigation the first four to six weeks after planting if the field catches a few good showers during that time. Much of the lower Southeast received heavy rainfall in April from multiple storm systems, but in May as planting hit the high gears, dry conditions fell over much of the region. As of May 18, for example in Georgia, about 48% of peanuts had been planted and 41% of cotton, according the USDA National Agricultural Statistics Service Southern Regional Field Office.

What were your soil sensors reporting?

"We can sometimes be guilty of placing a sensor in the row of the cotton, let it start logging data, making decisions from that data and assuming everything is good to go. Unfortunately, we need to make sure we know what is going on in the field before we blindly start following the sensor," says Wes Porter, University of Georgia Extension engineer and irrigation specialist.

Porter, Cale Cloud, UGA Extension water agent, and David Hall, UGA Extension water educator provided a way to accurately weight soil moisture sensors throughout the season, but something which is especially helpful early in the season. You can get additional irrigation tips in UGA Cotton Team newsletter.

It helps to see the whole plant, roots and all. For example, a seven-inch cotton plant could sit on about a foot of roots. A 12-inch plant, or about 30 days after emergence, could have 22 inches or more of root. A 16-inch plant, or 50 days after emergence, can have a root system stretching three feet.

Most sensors come with two or three depths to measure moisture. Moisture sensors generally default to an average of the sensor's readings at different depths to determine an irrigation trigger. This can provide false water needs for young cotton plants.

For example, say the 16-inch sensor depth shows a dry reading while the sensor's 8-inch depth shows adequate moisture. The average of the two could trigger a call for irrigation. But in a field with young plants fully emerged, which would have about 8 inches of roots, the sensor's call for irrigation may be wrong.

Considering the plant’s root depth can help weigh the sensors data for a better decision. According to the UGA Extension specialists, early in the season, the 8-inch sensor can be given an 80% value and the 16-inch sensor 20%.

In our scenario above with a young cotton plant, giving a higher percentage weight to the shallower sensor verifies no need for irrigation. By adjusting the sensor's weight value throughout the season, growers can make better decisions from good data.

Here are the UGA Extension suggestions for weighting sensors during the cotton growing season. "But keep in mind these are only observed suggestions and root growth and development will depend on individual soil type and growing condition and may vary, it is strongly suggested a grower use local knowledge to appropriately weight their sensor depths for irrigation trigger points," Porter said.

D1 = shallow sensor D2 = middle sensor D3 = deepest sensor

  • Early Season: 80% * D1, 20% * D2, 0% * D3

  • Early-Mid Season: 60% * D1, 30% * D2, 10% * D3

  • Mid Season: 50% * D1, 25% * D2, 25% * D3

  • Late Season: 40% * D1, 30% * D2, 30% * D3

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