Sensor-Based Irrigation Proves Its Worth

It has been estimated that 70 percent of the world’s fresh water consumption is directed toward irrigating crops – all crops, not just cotton. But that water is dedicated for good reason – yield!

“Irrigation accomplishes two goals,” says Dr. Ed Barnes, Director of Agricultural and Environmental Research for Cotton Incorporated.

“Irrigation can boost yield, as well as stabilize yield and quality by ensuring adequate soil water during critical times of the growing season.”

In the sandy Coastal Plain region of the Southeast, irrigation has been shown to nearly double cotton yields from non-irrigated land.

“Irrigation in the Southeast can bump up yields from 750 pounds to nearly 1,500 pounds of lint per acre,” adds Barnes.

As production costs continue to rise and regional drought conditions strangle yield, adding irrigation to your operation to supplement rainfall in humid areas and improving irrigation water management in arid regions is becoming almost essential to help producers stay competitive.

“Risks associated with yield instability can be somewhat mitigated by irrigation, which can help producers estimate annual yields (and thus returns) – allowing more financial planning on the part of the producer,” Barnes says.

Sensor-Based Irrigation Scheduling

Results from Cotton Incorporated’s 2008 Natural Resource Survey indicated only about 10 percent of the responding producers used weather-based scheduling tools or crop soil monitoring systems. One of the challenges with which producers have been faced is the time it takes to travel to a field and record output data from irrigation sensors. The recent availability of newer systems incorporated with more affordable wireless data transmission capabilities are today making it more practical.

Three physical properties can be measured by sensors to help alert producers when to irrigate.

• Soil Matric Potential: How tightly water is bound to the soil. The higher the matric potential, the more stress the plant is under.

• Volumetric Moisture Content: A measure of water volume per volume of soil.

• Canopy Temperature: A measure of the cotton plant’s leaf surface temperature (as shown in photo above).

The relationship between matric potential and moisture content is very soil specific and is best determined from soil core samples collected with minimal disturbance.

“It’s easier to interpret when to trigger irrigation with matric potential because there are soil-specific thresholds already established for cotton,” says Barnes.

When To Pull The Trigger

Volumetric measurement requires some site-specific calibration to determine when to pull the irrigation trigger and is based on water currently available to the plant. The soil’s water- holding capacity is defined as the difference between the water content at a field’s capacity (low tension) and a plant’s wilting point (high tension). The formula for Percent Plant Available water (PAW) equals 100 x (Measured soil moisture) minus (Moisture at wilting point)/(Field capacity) minus (Moisture at wilting point). Often, a PAW of 50 percent is used as an irrigation threshold for cotton.

Canopy temperature is slightly more difficult to interpret for irrigation timing – especially in humid regions.

“When the air is moist (high humidity), the amount of evaporative cooling is reduced – even for cotton that’s got plenty of moisture,” says Barnes.

Researchers are still attempting to determine the appropriate use of canopy temperature for cotton growing in humid regions, but it’s a great tool for determining irrigation timing in arid regions from West Texas to California.

If information is power, then cotton farmers who utilize an appropriate sensor-based irrigation scheduling system are already way ahead of the curve and are also maximizing their irrigation efforts.

The Cotton Board, which administers Cotton Incorporated’s Research and Promotion Program, contributed information for this article.

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