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Irrigating your corn? Don't stop too early

New research shows that corn growers who irrigate should continue doing so into the grain-fill stage. Stopping too soon can cause significant yield loss, a company report says.

A four-year field study by Kansas State University and Pioneer Hi-Bred International, Inc., was conducted in northwestern Kansas to evaluate effects of delaying the first irrigation or premature termination of the irrigation season on corn grain yield and its physiological components.

The study results confirmed the corn vegetative stage prior to tasseling is the least sensitive to water stress while the grain-filling stage is highly sensitive to water stress.

"The grain-filling stage is the second most critical stage in corn with pollination being the most critical." says Freddie Lamm, research irrigation engineer for K-State Research and Extension. "Yield can be negatively impacted during grain fill by weather conditions such as excessive heat, solar radiation, wind and lack of rain. Late-season irrigation is one tool that can be used wisely to minimize any negative weather effects so grain filling can continue and not be ended prematurely."

Corn kernels are formed and experience rapid growth during the last 60 days of the growing season right up to maturity, and readily available water is a necessity. "Daily yield gains of four to five bushels per acre are possible under good growing conditions during grain fill and daily yield increases of two to four bushels per acre are common," says Lamm.

"Growers need to look at several factors before beginning an irrigation event," says Tom Doerge, Pioneer agronomy research scientist. "This includes reviewing the types of soil for each field, looking at how well that soil stores water reserves and also the stage of the corn."

After reviewing these factors, local past experiences with late summer weather and crop maturity should be considered.

Irrigation is a costly procedure with today's energy prices and sometimes uses scarce water resources, so it is understandable that producers would want to stop irrigating as soon as practical, says Lamm. Results from this study, however, show that when needed, an inch of late irrigation often can increase corn yields by 20 bushels per acre.

"Irrigation planning should be based on sound information about the crop, soil water reserves and weather conditions," says Lamm. "A specific calendar date for ending the irrigation season may be the worst choice. Producers need to be flexible and make decisions about the last irrigation event based on anticipated crop water needs and rainfall."

Long-term field studies and climate-based calculations of corn water use during the last three weeks before maturity indicate that an average of three to four inches occurs in western Kansas. This water use can be obtained from a combination of soil water reserves, rainfall and irrigation.

"One problem that occurs is that producers sometimes rely too much on soil water reserves that may have become overly depleted during the season" says Lamm. "Past studies have suggested soil water reserves could be depleted as much as 80% during the final stages of corn production without harming yield.

"That has not been our experience in this study. Yield reductions began to occur when available soil water reserves were as high as 50%. It seems likely that with the great corn hybrids and other advanced production technologies we have today, that less water stress can be tolerated without an appreciable economic impact. For example a five-percent reduction on 125-bushel-per-acre corn is much less important than a five-percent reduction on 225-bushel-per-acre corn."

"This type of research offers growers sound agronomic advice on how to better manage their irrigation schedules," adds Pioneer's Doerge. "The research is particularly valuable to those who are impacted by declining water sources."

New research shows that corn growers who irrigate should continue doing so into the grain-fill stage. Stopping too soon can cause significant yield loss, a company report says.

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