Irrigation is an essential tool for growing high yielding, high value cotton and grain crops in the Southeast. In many cases managing irrigation is tantamount to managing the profit of a crop.
Ongoing work by Clemson University researchers indicates several new techniques can allow growers to more efficiently use water and increase crop yield and quality.
One of the first variables to look at in irrigation efficiency, says Clemson Agricultural Engineering graduate student Chris Bellamy, is the topography of the land to be irrigated.
Many fields in the Southeast have varying degrees of compaction from farm equipment. Typically, you don’t want to apply as much water on the higher slope of the field as the lower, because you lose a lot of that water to runoff on these compacted areas.
“Variable rate irrigation is one way to overcome compaction and to get more uniform water application. Using zone mapping and management with GPS and GIS technologies, we can determine where in a particular field that quantities of water should be varied,” Bellamy says.
“In the Southeast, perhaps more importantly on Coastal Plain soils, soil type variability along with soil profile variability make it critical to adjust water application amounts to account for these changes throughout the field,” he adds
The Clemson researchers are also looking at Low Energy Precision Application (LEPA) systems to apply irrigation water. This involves using drop nozzles from a center pivot irrigation system in which irrigation water is actually applied below the crop canopy.
“LEPA is new to the Southeast, though it has been used extensively in other parts of the country. By dropping the nozzles down into the crop, growers can reduce wind and evaporation variability of irrigation water.
“The LEPA system can also apply water in different patterns — some high, some straight out, and some straight down. At different stages of growth in cotton, for example, we want to get as much soil coverage as possible with the exception of the wheel tracks where water will be lost to runoff,” Bellamy explains.
“As of September 2009, there are 46 variable rate irrigation systems operating in Georgia and South Carolina. So far, growers love the cost savings and crop benefits. Most of these growers had significant runoff issues with their irrigation water and these systems really make a difference,” he adds.
Luray, S.C., grower Bud Bowers is one of the farmers who works closely with the Clemson research team and uses the LEPA system. Soil variability and compaction were major problems on his farm — as were a shortage of labor and travel costs associated with starting, stopping and adjusting his 10 center pivots daily.
“I know variable rate application has made me a better farmer. I take more soil samples and I just know more about what is going on in my fields. The immediate benefit is uniformity in my crops. I have seen yield increases using variable rate irrigation, and there is no question it saves in water and energy costs,” Bowers says.
In testing in other parts of the country, LEPA systems were also highly rated in maintaining moisture content in irrigation water. In tests in Texas, LEPA center pivots maintained 90-95 percent irrigation system efficiency, comparable to drip irrigation, which was highest at 90-98 percent.
In conjunction with the LEPA system, the Clemson researchers have used a dammer diker to create gallon-size reservoirs that track the irrigation system. Water pools in these ponds while the irrigation system is running, allowing it to infiltrate and get to the root system of the plant.
The best time to pull the dammer-diker through a field is just before you put on the first irrigation water. The machine builds the gallon-size dams on every other row, which is where the irrigation drops are on the pivot. Unless a quarter inch or so of water is applied after the dammer-diker is pulled through the fields, the small dams tend to fill in with soil.
“The first time we used the machine, we got a heavy rain, so we didn’t run the irrigation system. The dams filled in and we didn’t get much benefit from the dammer ponds. Subsequently, we went ahead and ran the irrigation system as soon as we finished pulling the machine through the field and the dams held up in heavy rains,” Bellamy says.
A subsoiler is mounted in front of the dammer-diker and the machine builds the gallon-size dams at about a five-inch depth in the soil.
When to irrigate is essential to maximizing irrigation water usage. Some growers feel the soil, some use tensiometers, others rely on weather forecasts — there are a number of systems used to determine when to irrigate.
The Clemson researchers use sophisticated electronic soil sensors that Bellamy says allows them to irrigate right on target, getting higher yields than with any other method of determining when to irrigate.
“There is more up-front cost in buying the electronic sensor and if preferred, buying a solar panel and telemetry system to allow data collection to be preformed from the office or other location. Despite these costs, Clemson researchers increased yield enough to save a net of $24 per acre on irrigation costs in cotton,” he says.
In cotton precision irrigation work, the Clemson research team is using the most current varieties, including the Class of 2009 DPL varieties, replacing DPL555 and DPL147, which are being phased out.
“DPL0924 had the highest water use efficiency of all the varieties tested in 2008. Regardless of the cotton plant’s water use efficiency, over-watering can actually reduce efficiency. Using electronic sensors provides an efficient way to keep up with water usage and apply water only when the plant needs it.
“In our tests, you can look out over the field and you can easily pick out the plots of cotton that have had no irrigation water. By early September, the non irrigated plots stood out in “blocks” of cotton with very pale leavess. These plots also often stand out due to an increased number of white flowers in the tops of the plants compared to the irrigated plots that have not produced white flowers this high yet.”
With the cost of irrigation on cotton running from $50-$60 per acre and cotton prices hovering around 70 cents a pound, it is critical for farmers to maximize efficiency of irrigation.
Water is a commodity that Southeastern growers often over-look. Severe drought throughout the region in 2007 and 2008 gave many a new perspective on cost and return of irrigation. The demand for high crop yields to maximize high crop values continues to create more interest in irrigation.
Figuring out the most precise usage of irrigation water is critical for both economic and environmental reasons.
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