Subsurface drip irrigation depends on developing master plan SUBSURFACE DRIP irrigation, SDI, could help farmers stretch scarce water resources and increase yields, but engineers say success depends on developing a master plan for how and where the system will operate.

"We recommend farmers do a lot of soul searching before they install a subsurface drip system," says Mike Buxkemper, president of Watermaster Irrigation Supply, Lubbock.

Buxkemper discussed SDI design factors during a recent Texas Agricultural Irrigation Association seminar in Amarillo.

"For one thing, a farmer needs to know what crops he'll grow with SDI for several years in the future," he said. "Row spacing for underground drip systems can be quite variable. For 40-inch cotton rows, we recommend 80-inch tape spacing. For 30-inch corn rows, we'd put tape 60 inches apart."

He said the permanent nature of SDI systems (tape may last 20 years or longer.) mandates that farmers develop a master plan for crop rotation.

He also advises growers to map out the area to be irrigated and identify the field dimensions, the topography, and soil characteristics. All may influence system design.

He emphasizes that growers assure themselves an adequate water source.

"Wells, for instance, come with a lot of challenges. Availability may drop off late in the year and farmers can't change nozzles to meet the variable water flow. They have to consider the flow rate up front and plan accordingly."

Buxkemper says irrigators normally overestimate water quantity by 25 percent. He says a flow meter is essential "for informed decisions regarding crop selection and system design."

He said farmers often err on the high side with water quality.

"They have to know the chemical properties of the water, too." he said. "We can't filter out what's part of the water, but we may treat it chemically. Calcium carbonates, iron, nitrates and boron may cause water problems for SDI systems, if not properly treated."

"Filtration is a key,"he said.

Jerry Funck, an engineer with NetaFim USA, says filters on SDI systems provide an "insurance policy and affect how long the system will last. Install adequate filtration but not more than necessary. Also, never fix a clogged filter problem by installing less filtration than is needed."

Funck said a number of filtration systems are available and farmers should study each, in relation to specific field conditions, to select the best for each site.

"SDI can be a lot better than other irrigation options," Funck said. "But management is the key. Farmers must know soil types, texture and depth across the field and then determine water flow rate to develop an adequate system. "Water holding capacity is important in determining irrigation frequency."

He said an SDI system will not water the first year the way it will in later years. "We advise farmers to install systems as early in the year as possible to allow soil to settle before they begin to irrigate."

He agrees that flow rate is critical. "Does the water supply decrease at the end of the season? If we know it's coming, we can manage for the decrease," he said. "But we have to plan for it and know when the peak crop needs will be."

Funck says shutting a system on and off also demands preparation. "When we see the crop stressing, we've waited too long to initiate irrigation," he said. "Stress is present before its visible in the crop. Use soil probes, a shovel, or other device to determine soil moisture content."

He said watering cotton later into the season may allow a farmer to mature bolls that would otherwise detract from quality. He says 50 percent to 80 percent cracked or open bolls is a good standard.

Funck also recommends ratcheting up insect and weed control with SDI.

"We can't afford flea hopper losses with underground drip systems," he said. "Three sprays, at a cost of $25, can save a bale of cotton. Set a lower threshold for insect control with SDI."

He said weed control is not complicated and farmers should "keep fields clean."

Funck emphasizes the importance of setting an early cotton crop and maintaining a heavy boll load. "Light applications of a growth regulator at the right time will be an advantage. Proper timing could mean using less with SDI systems."

He says cotton variety selection improves with SDI, too. "We can move to a more indeterminate variety because we can mature it quicker. Picker types have done well with SDI systems.

"We want varieties with good early vigor and high yield potential. A farmer should select the best variety for the particular field."

Cotton is not the only crop that can benefit from SDI. Funck and Buxkemper cite corn, onions, sorghum, wheat, peanuts, cabbage, melons and peppers as other crops that work well with this system.

"With peanuts, farmers will want to use 40-inch tape spacing and water enough to bring moisture up during pegging."

Observers estimate that farmers have installed SDI systems on as many as 45,000 acres in the Texas High Plains.