Irrigating dry beans 2008 style

Nebraska

It's June, and dry edible bean producers find themselves faced with a familiar question: "When should I use my irrigation water?"

Normally, the first irrigation would take place during the last week in June, says Dean Yonts, irrigation specialist at the University of Nebraska Panhandle Research and Extension Center. But since the beginning of the drought, farmers have learned that they cannot count on spring rains to water the crop until then.

And even after the drought ends, some growers' water still might be limited by regulations, as NRDs and the state try to bring water consumption into compliance with LB962 and interstate compacts.

Luckily, the knowledge base of how dry edible beans react to water stress at different points in the growing season has grown in recent years, and will continue to grow. Yonts and his colleagues at UNL have been conducting research for more than a decade about the effect that water stress has on bean yields.

Based on the data to date, Yonts' advice is: "Don't let that first irrigation be delayed too long because that is when the most damage to your potential yield can occur."

Yonts notes that many irrigation practices have changed, as bean growers have adapted their methods in recent years in response to water shortages and other factors. In the process, they have discovered that they can have some water stress, yet still end the season with very respectable yields.

One factor in this adaptation is the influx of center pivots to the North Platte Valley, which allow growers to time irrigations differently and control the amount of water applied. Furrow irrigators have determined that shorter set times are necessary to stretch their water allocation, although labor is still a concern. Outside the valley, many growers are faced with pumping restrictions.

Just as growers have learned and adapted, research has also been progressing. In fact, research on the impact of water stress on dry beans began in the mid-1990s. As a result, there are more than 12 years of data.

One of Yonts's first experiments studied how water stress affects dry beans early in the season--specifically, the importance of the first irrigation. His research indicates that delaying irrigation by even one week when the crop needs water can reduce yield by 5 percent (based on a normal first irrigation of around the last week of June). Delay two weeks and that number doubles. And it can get even worse, up to a 20 percent reduction--especially if the irrigation system cannot keep up with crop demand as the beans move to the greater water use period of growth. Yonts points out that this would be the case with many center-pivot systems that have capacity limitations.

Research on late-season water stress showed similar results. Shutting water off around Aug. 10 could reduce yields by 5 to 10 percent. Because crop growth is near the end of the season, yield reductions weren't much greater than 10 percent.

So in these two cases, Yonts said, the higher risk of having additional water stress at the beginning of the season points to early-season irrigation being much more important than late-season.

Delaying irrigation also affected the rate of plant maturity, the irrigation specialist said. Early in the season, it resulted in a delay in plant maturity by as much as 3-4 days. Water stress at the end of the season also delayed maturity, but it was not as pronounced.

A delay of a couple days in rate of plant maturity may not seem important--until a storm comes along.

Currently, research at the Panhandle Center is focused on the impact of water stress during the middle of the growing season, when the plants are blooming and pods are setting and filling. In that experiment, water was withheld for periods of nine and 18 days.

With one year of research left, results to date indicate that a nine-day water stress period affects yields similar to delaying the first irrigation by two weeks. However, an 18-day stress period had a much more pronounced effect, according to Yonts, especially for center pivots compared to furrow, because of the inability to keep up with crop water demand.

Starting in 2009, dry bean water stress research will focus on water stress that will extend over the entire growing season.

The Panhandle Research and Extension Center is on the World Wide Web at www.panhandle.unl.edu.

7/14/08
4 Star NE\12-B

Date: 7/10/08

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