>From the eastern half of Kansas to the Atlantic Coast, annual >precipitation averages 36" or more - twice as much water as a corn or >soybean crop needs.

If the moisture comes when the crop needs it, that is. Tasseling corn requires up to 1/3" of water per day, and soybeans at pod-fill demand nearly that much.

Nature can be notoriously stingy with midsummer rain, and being equipped to make up the moisture shortfall can be the difference between a decent crop and a disaster in a drought year.

"In a poor growing season, just an extra 2-3" of water applied in a timely fashion can virtually double corn yields," says Dan Rogers, Kansas State University ag engineer. "There's especially a benefit to irrigation in southeastern Kansas, where we have light soils that do not store water well and where we can expect a period of drought about every summer."

In recent years, irrigation has increased faster in Missouri than in most states, and Joe Henggeler, state irrigation specialist, expects acreage to jump another 15% in 1998. The relatively dry summer of 1997 made irrigation a paying proposition, and that experience will encourage other farmers to install irrigation, figures Henggeler.

Irrigated corn earned $19.78 per acre more than dryland corn last year, reports Ray Massey, University of Missouri ag economist. Irrigated main-crop soybeans brought in $3.72 more per acre. The real boost came with irrigated doublecrop beans, which beat non-irrigated beans by $30.86 per acre.

Boosting the yield of beans after wheat spurred Southeastern farmers to install irrigation systems. However, in recent years, the trend has slowed.

"We have good water resources; the Tuscaloosa aquifer lies under most of the Southeast plains," says Jim Palmer, Clemson University soybean specialist. "And we know from our studies on irrigation that we can get 10-12% increases in yield with both corn and soybeans, even in years with good weather.

"I suspect current economics has slowed irrigation development," Palmer adds. "If we saw sustained prices above $7 beans and $4 wheat, we'd see renewed interest in irrigation."

But there's a high premium for this kind of drought insurance. Depending on the system installed and the cost of developing a water supply, irrigation requires an investment of $450 to $500 per acre. That's a big ticket to pay based on one year's dry-weather disappointment.

"Supplemental irrigation cannot be justified simply on the basis of increased yield in one year," says Kerry Harrison, University of Georgia irrigation specialist. "No one crop is likely to show a profit on irrigation. If you're doing everything else right - fertility, weed control, insect control - control of moisture may be the last bar to optimum crop production, which makes irrigation a good option to consider. But irrigation alone is not going to make you a better crop manager."

However, crop producers with better-than-average management find that a hedge against dry weather pays off most years."I put in irrigation against a total crop bust in a dry year," according to Ron Kuhlmann, who grows corn and soybeans in the Sangamon River bottoms near Beardstown, IL.

"The first year after we put in center pivots, I planted corn in the same fields; part of it irrigated, some not irrigated," reports Kulhmann. "With only 3" of water through the rig at tasseling, irrigated corn made 25 bu/acre over dryland corn."

Best thing about irrigation: It eliminates bust years.

In Missouri, Henggeler budgets $44/acre/year for installation costs, amortized over 20 years. Energy for pumping averages $8/acre, while repairs and maintenance add another $5. In that state over the past 18 years, irrigated corn yielded nearly 42 bu/acre more than dryland corn. Irrigated beans showed an 11-bu advantage.

"With soybeans priced at $6.50 per bu, that gives you about $72 more per acre to spend for irrigation," he says. "And that's the long-term average. When you hit a year like 1997, the margin of profit over irrigation costs is considerably better."

"However, soil type greatly affects the yield difference between dryland and irrigated fields," Henggeler adds. "On sandy soils, irrigation can add 25%. On clay or deep soils, the yield bump may be considerably less. In 1997 in the Missouri Bootheel, average yield increases on sandy, silty and clay soils were 15%, 12% and 8%, respectively."

Henggeler computed break-even prices for crops grown in southeastern Missouri last year. Factoring in the increased cost and higher yields, break-even for irrigated corn was $2.57 per bu, compared with $3.02 per bu for dryland corn. The break-even price was $6.75 per bu for irrigated soybeans; $7.92 for dryland beans.

"The big variable in deciding if irrigation will pay is the cost of developing water," according to Dan Rogers.

He points out that the cost of wells can range from $3,000 in alluvial floodplains to 10 times that or more in some areas.

"We have about 50,000 acres under irrigation in northeastern Kansas, most of it in the good water of river bottoms," he says. "Now, higher upland farmers are having to build surface impoundments, and that can run up the bill considerably. If we had more available water in the eastern part of the state, we'd see a lot more irrigation go in."

But given a good water supply, a grower who has already fine-tuned other elements of crop management might put a profitable pencil to irrigation.