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Corn+Soybean Digest

Make Irrigation Pay

Irrigation just didn't add up for many Midsouth soybean growers in 2006, with five to six applications resulting in high costs and little improvement in yields.

For example, one Mississippi soybean grower furrow-irrigated his maturity group IV soybeans five times this past year. His irrigated acreage averaged 32 bu./acre while his non-irrigated acreage averaged 22 bu./acre.

That means he spent an estimated $37.50 on irrigation to harvest an extra 10 bu. of soybeans valued at about $60. What's more, both his irrigated and his non-irrigated yields were about half of his five-year averages.

This scenario played out in 2006 more often than most soybean producers care to remember, and some are still trying to glean a lesson from the difficult experience.

Agronomist Dan Poston at the Delta Research and Extension Center in Stoneville, MS, says he isn't interested in reliving 2006, but maybe there are lessons to be learned. “It was a tough year. There is no doubt that water management was the difference between high-yielding soybeans and low-yielding soybeans,” he says.

“Many folks started too late and didn't water frequently enough,” Poston explains. “As we have moved more and more towards early planting, we have had a difficult time convincing producers that one of the consequences of early planted and early maturing soybeans is that they often need irrigation early in the growing season.”

One mindset of traditional production systems was that you never started watering beans until July 4th.

That's no longer the case, according to Poston. Many Midsouth soybean growers need to begin irrigating early production system soybeans in late-May or early June.

Poston recommends producers shift away from flood irrigation to faster methods like border or furrow irrigation. “Farmers often say they can't afford to water six to eight times compared to three to four times. They forget that watering eight furrow or border runs at 24 hours per run is the same amount of water as four flood irrigated runs at 48 hours per run,” he says.

“At Stoneville in 2006 we began irrigating some early planted fields May 20 and remained on a seven- to nine-day irrigation cycle for most of the summer. We watered some fields nine times using short run cycles so the total water wasn't as much as it seems. The key is timeliness and frequency of irrigation. Many of these heavy clay fields in our trials cut 80-90 bu./acre.”

Roger Carter, Louisiana crop consultant, agrees that there are times when irrigation initiation may be delayed, but says the reasons for the delay may be economic. “High fuel, poly pipe and labor costs have deterred many a farmer from beginning irrigation when he can see a cloud on the horizon. Delaying the first irrigation is usually the first mistake made. The second is frequency,” he says.

However, Carter says growers in his area are dealing with high insect and disease pressure, and he attributes much of the lack of yield increases to Cercospora and stinkbugs, primarily the red-banded stinkbug.

“Irrigated soybeans in a dry year are like a magnet attracting stinkbugs, and pivot irrigation will enhance many diseases,” Carter adds. “Therefore some of the failures of irrigated soybeans in Louisiana to respond to water can be blamed not on the farmers' decisions, but on two severe pests. There is really no sure way to control Cercospora. Red-banded stinkbugs may build to threshold levels five or six times during the year. Each time they do, yield is lost.”

Whether the cause is irrigation timing, or insect and disease pressure, Poston says what is crucial to the developmental process of the soybean plant is a stress-free environment during the R3 growth stage. “Anything you can do to minimize stress and help boost the growth of that plant at R3 is critical. I can't stress enough how important this is to the success of a crop,” he says.

Knowing when the critical stages of growth are occurring is vital, Poston adds, in order to minimize stress and provide adequate water to the plant when it needs it the most.

Lower yields in 2006 also can be attributed to drainage issues. “Year in and year out, growers will make more money producing soybeans if they can successfully manage the relationship between irrigation and drainage,” he says.

One method for improving drainage, says Poston, is planting on raised instead of flat beds. “In our 2006 on-farm research trials, we documented a $50/acre net response simply by improving water drainage with raised beds,” he says. Poston's on-farm research was conducted in the central Mississippi Delta on heavy and mixed Sharkey Clay soil.

Using deep tillage where needed also can be a remedy to drainage problems, he says. “We've got to decide how much tillage is needed and when it is needed. But in some no-till situations, deep tillage may be necessary to improve drainage,” says Poston.

Obtaining higher soybean yields involves a multitude of factors, including picking the right varieties, planting them where they best fit and spending money on economically viable inputs, Poston says.

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