Soybean South

 - Irrigation -

Watering Beans In The South

Plant early maturing varieties before May to realize maximum yields
from irrigation in the southern United States. For these early plantings,
start watering no later than R3.


By Larry G. Heatherly

Irrigation of soybeans in the southern United States is a management option for increasing yields and ensuring consistent production from year to year. Its use is governed by its cost in relation to expected increase in returns.

The 2002 Census of Agriculture reveals a marked difference between southern regions in the use of irrigation for soybeans. In the Mid-South or Delta states of Arkansas, Louisiana and Mississippi, 43 percent of the soybean acres were irrigated. In the southeastern states of Alabama, Georgia, North Carolina and South Carolina, only two percent of soybeans were irrigated.

The limited irrigation in the Southeast is through center-pivot systems. The University of Georgia enterprise budget estimates the total cost of irrigating soybeans at $137.50 per acre.

Georgia Extension soybean specialist Phil Jost states that irrigating soybeans isn’t cost effective at projected yield levels in the southeastern United States. “If a producer installs a new overhead irrigation system in Georgia, I seriously doubt he would put beans under it,” says Jost. “With a projected 50 bushels per acre soybean yield from an irrigated production system, our budget analysis estimates the total cost breakeven price to be $7.21 per bushel. Conversely, the total cost breakeven yield is over 60 bushels per acre.”

Jim Dunphy, North Carolina Extension soybean specialist, concurs with Jost’s assessment. “In the 1980s, we conducted 38 tests across the state,” Dunphy says. “Our check (nonirrigated) yields were greater than 50 bushels per acre, and we realized only a one bushel per acre yield increase with each irrigation. That was not economical.”

Irrigated beans fare well in the Mid-South
Irrigation in the Mid-South uses surface methods (furrow, flood and border). Mississippi State University enterprise budgets estimate irrigation costs at between $71 and $74 per acre. Profits from properly irrigated soybeans consistently exceed those from nonirrigated soybeans primarily because of early planting and lower costs for using surface irrigation.

John Gourlay border irrigates nearly 1,700 acres of soybeans in Bolivar County, Miss. He applies water down every other furrow starting at about R1 (beginning bloom) and continues until beans are “squared”or fill the pod cavity (R6).

“We realize about 20 bushels per acre increase in yield from irrigation,” says Gourlay. “In 2005, all of our irrigated fields were in the 65 to 70 bushels per acre range.”

Obtaining maximum yields from irrigation in the southern United States requires planting early maturing varieties before May. For these early plantings, irrigation in an average year should be started no later than R3 (beginning podset).

Rain and soil moisture should be monitored to ensure that the effective rooting zone (18 to 24 inches) has adequate water (>50 percent available) to maintain optimum growth before R3, especially for sandy soils such as those of the southeastern Coastal Plain.

Irrigating later-maturing varieties
For May and later plantings of later-maturing varieties, irrigation should be started at or near R1.

Soybeans planted behind small grain in a doublecrop system should be monitored for drought stress conditions (<50 percent available water in rooting zone) before the R1 stage to ensure that rain and soil moisture provide adequate water for vegetative growth.

During the irrigation period, soybeans typically use about a 0.25 inch of water per day.

Soil-recharging surface irrigation should be scheduled to meet this requirement when no more than two inches of soil water has been depleted. This will require an 8 to 10 day re-irrigation schedule in the absence of rain.

Re-irrigation with overhead sprinkler systems is typically timed to system capabilities rather than to available soil water.

Thus, a system designed to apply a net of one inch per acre per day should be scheduled to irrigate every four days in the absence of rain to replace depleted soil water.

Irrigation should be terminated at or near R6. A soil-recharging irrigation or wet soil at this time will supply enough water to finish filling seeds and maximize your soybean yield.

Larry G. Heatherly is a freelance writer based in Seymour, Tenn. Contact Heatherly at (865) 573-6295 or

By Jason L. Jenkins

The decision to stop irrigating soybeans and corn is never black and white – or easy. Turn off the tap too soon, crop yields suffer. Turn the water off too late, profitability is reduced.

Either way, it’s money down the drain.

How far back from maturity to apply the last irrigation is a question many have tried to answer in the past, says Joe Henggeler, MU Extension irrigation specialist at the Delta Research Center in Portageville, Mo.

“Other Midwest universities have developed guides for timing last irrigation using a series of calculations where farmers are asked to input everything from the crop’s water requirement to the depth of the root zone to the water-holding capacity of the soil,” he explains.

“The problem is that these guides are complicated, and you can’t always count on a mathematical back-calculation because things are always happening in the system.”

Farmers want a a good rule of thumb for terminating irrigation, not a complex math equation, Henggeler says.

“What we’re trying to develop is a set of photos that show what the crop should look like before terminating irrigation on different soils,” he adds. “This technique simplifies the decision by saying, ‘If it looks like this, cut off irrigation.’ Then you don’t have to worry about dates or anything else.”

‘Five-bushel bump’ noted
During the past three seasons, Henggeler has experimented with cutting off irrigation at different dates in both soybeans and corn on three different soil types – sand, silt and clay. The study has used several varieties of 114-day corn and maturity Group V soybeans under overhead sprinklers.

“We’ve found that overall, folks have been cutting off irrigation way too early in soybeans and just a little early in corn,” he says. “Rather than terminating when beans are beginning to touch the pods in the R6 growth stage, irrigation should be maintained until the pods reach beginning maturity. We’ve seen about a five-bushel bump per acre by extending irrigation from R6 to R7.”

Once Henggeler gathers all of the data, he is going to work on developing a flashcard-like guide that farmers can use. For each soil type, pictures of a cross-section of an ear, a husked ear, an unhusked ear and the overall canopy will be included for corn. Pictures of pods, the last four nodes on a plant and the overall canopy will be included for soybeans.

“We engineers don’t mind all of those formulas, but producers want a guide that they can use without all of those calculations,” Henggeler adds. “They will be able to just pull this guide out of the glove box when they need it and leave the calculator at home.”

Jason L. Jenkins is with Extension and Ag Information at the University of Missouri. Contact Jenkins at (573) 882-2980 or e-mail him at

Coming Soon: A Pictorial Guide To Cutting Off The Water

Missouri irrigation specialist Joe Henggeler plans to test his visual technique for determining when to terminate irrigation for soybeans and corn one more year before making an official recommendation.

“Soybeans are a lot easier to identify and communicate the exact stage they are in vs. corn, where you go from beginning dent to full dent with a big time frame in between these stages,” Henggeler says.

“Also, everyone may not agree on what full dent is.

“On the other hand, with soybeans, stages R6 or R7 happen pretty quickly,” he says, “and you can definitely identify R6 where we see some yellowing of the leaves.

“We’re coming up with a recommendation for terminating irrigation,” Henggeler notes, “but I want to go through our pictures again to make sure we can say it photographically.”

In Henggeler’s opinion, some of the recommendations found in Extension publications recommend cutting off the water too early on beans and corn. Before cutting off irrigation water, he says the soybean leaves need to be touching really well and there should be some yellowing appearing in the foliage.

“Clear up until that time, you can still realize a yield increase,” Henggeler explains.

– Carroll Smith