If ever there was a year built for conducting irrigation field research in the lower Southeast, it was 2010, with record-breaking heat and prolonged drought in many areas.

As growers struggle to meet the dual demands of providing enough water for their crops and maintaining efficiency, subsurface drip irrigation is attracting more interest. In one trial conducted by Auburn University in southeast Alabama, corn yields this past year were doubled in subsurface drip-irrigated fields versus dryland fields.

According to a recently published report, a subsurface drip irrigation (SDI) demonstration was installed on the Wiregrass Research Center (WREC) in Headland, Ala., in late spring/early summer 2009. The site has slightly rolling topography with one or two terraces.

Growers are encouraged to visit this location throughout the year and see how subsurface drip irrigation works on the light, sandy soils of southeast Alabama.

Six plots, each 950 feet long by 48 feet wide, were established for a three-year irrigated and rainfed (dryland) rotation of corn, cotton and peanuts. The six plots are grouped into three two-plot blocks. Each block has a 16-row rainfed (dryland) plot and a 16-row irrigated zone.

Each irrigation zone has 15 mil. drip tape lateral buried between every other row at 15 inches deep (eight drip laterals per irrigation zone). John Deere Auto Steer was used during installation to allow future drip tape location. With 0.26 gallons per hour (GPH) emitters spaced every 2 feet along tape length, design tape flow rate was 0.0022 gallons per minute (GPM) per foot. Each 1.07 acre irrigated zone requires 16.81 GPM (15.73 GPM per acre).

Irrigation water is supplied by a 3-horespower submersible pump with pressure tank control, installed in a farm pond approximately one half mile from the site. A 2-inch time and pressure automatic cleaning filter provides clean water to the three irrigated zone control heads. An irrigation controller for zone control, a Watermark Monitor with Watermark soil moisture sensors, and a tipping bucket rain gauge were installed.

A low power field radio was connected to the Watermark Monitor to allow remote reading of received rain, soil moisture and irrigation operation from a desktop computer located in the WREC offices about 1,200 feet away. MoisMis2020, an Xcel-based irrigation scheduling program using crop growth curves, rainfall and Watermark soil moisture feedback was to be used to schedule irrigation for the three crops.

This report talks about rainfall, irrigation and corn yield results from the first two years of the demonstration.

In 2009, corn was planted on April 24, about three weeks later than normal. Drip tape laterals were installed April 23 but installation of manifolds, control station, main lines and pond water pumping station occurred over the next two months. Soil moisture sensors were not installed due to system start-up problems.

Manifold/lateral leaks were repaired and the first irrigation, a four-hour operational test, occurred on June 17, 2009.

Already under drought stress

This was day 54 after planting and the crop had already begun experiencing drought stress. The irrigation controller never worked throughout the season. All irrigations were manually started and stopped based on MoisMis2020 (an Excel-based irrigation scheduling program) recommendations without soil moisture feedback. Corn harvest was in early September.

In 2010, corn was planted on March 30. MoisMis2020 was started with a 120-day corn crop water-use curve. Three weeks into the season, field scouting verified crop growth to be six days ahead of the growth curve. The CropAdjust feature of MoisMis2020 was used to “shorten” the season by these six days. Soil moisture sensors were installed early May, about one and one-half weeks later than the “within 30 days after planting” recommendation.

The irrigation controller again failed to work and a second used controller was installed the last of May. It also failed and again, all irrigations were started and stopped manually the remainder of the season.

Thirty-one rainfall events totaling 14.08 inches were received on the SDI corn demo. Over 75 percent of the 31 rain events were smaller than one half inch. More than one-half of this amount fell by day 50 (May 19) and contributed to excellent early root development. No rain events greater than one half inch after day 84 hurt dryland (rainfed) yield development.

The first of 18 irrigation events totaling 12.7 inches occurred on May 21 (day 50). Ten irrigation events totaling more than 6 inches were applied from June 25 to July 20 during the critical dough to black layer formation period (day 87 thru 112) for this mid-season corn.

There were four checks within each treatment each year. These checks were compared and averaged to give the final dryland and irrigated corn yields.

Even though more than 26 inches of rain fell on the 2009 crop and only minor soil moisture deficit was experienced from mid-pollination through black layer development in both rainfed and irrigated corn, severe potential yield reduction had already occurred in the near 30-day drought in the six to 10-week growth period (four to 15-leaf development stages).

This was only partially overcome by late-started irrigation in the 14th leaf to tassel emerging stage. This 2009 season clearly demonstrated the need for earlier planting and being ready to irrigate as soon as drought develops.

Corn was planted March 30, 2010, more than three weeks earlier than 2009. Drought began to develop in early May within 30 days after planting. A 3.45-inch rain came too quickly on May 4 and contributed little to soil moisture available to the crop. Starting irrigation in response to this early season drought was key to the 170-plus bushel per acre 2010 SDI yield.

Early planting helped the rainfed (dryland) yield 80 bushels per acre, twice the late-planted 2009 rainfed yield of 40 bushels per acre with almost half the rain.

According to the report, these first two years of large-plot SDI irrigation at the Wiregrass Research and Education Center have demonstrated the ability of timely applications of irrigation water using a permanently buried drip tape system to more than double typical rainfed (dryland) corn yield.

A soon-to-follow life-cycle economic analysis based on WREC SDI Demo yields and installed and operational costs should highlight accompanying economic advantages of small-field SDI irrigation in the Wiregrass.

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