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Plan early for double-crop soybeans

Wheat acreage is up across the upper Southeast, indicating an increase in double-crop soybeans in the 2008 season. By making some critical management decisions now, growers can increase their chances of a top crop this fall.

In South Carolina some growers have had great success growing early maturity group soybeans, but drought, timing of harvest and other production practices are likely to keep that trend on the decline. The vast majority of soybeans planted in the state are likely to follow this year’s big wheat crop.

It just makes sense to double-crop beans behind wheat, says Clemson University Agronomist Pawel Wiatrak. From an agronomic standpoint, full-season beans will usually do better, but from a risk standpoint, having two crops makes a lot more sense than depending on one, he adds.

One of the first management decisions South Carolina soybean growers need to make is variety selection and buying seed. The drought last year created some problems for supply, but more importantly for seed quality.

“Growers may have some difficulty in getting soybean seed, especially finding a specific variety,” Wiatrak warns. Making variety decisions and buying soybean seed early may provide big benefits later on in the season, he adds.

In fields with a history of nematode problems, growers should take special care to take good soil samples and identify the type of nematodes. In these situations the first criteria for seed selection should be nematode resistance and second should be yield potential.

Growers, Wiatrak says, should look at local results and compare these to statewide soybean variety results and make their variety choice based on yield potential. In South Carolina, growers can find the county and replicated variety results at Or, they can contact their county Extension office.

Getting double-crop beans planted by July 1 is critical, because research has demonstrated yield goes down approximately a half bushel per day for every day past mid-June. Of course, this is highly influenced by the weather, Wiatrak points out, but is still a good reason to get double-crop beans planted on time, and if at all possible, no later than July 1 in South Carolina.

If planted past July 10, he strongly recommends beans be planted with a grain drill, using narrow (7-10-inch) rows. This gives soybean plants a better chance to overlap and to make better yields, despite the late planting.

Regardless of when soybeans are planted, planting in optimum moisture is critical, as is good seed to soil contact. Using disk coulters to open up and clean up the row and row packers to press the seed into the soil is good insurance for good seed to soil contact, Wiatrak says.

If growers have problems with hardpan, they should use deep tillage prior to planting wheat, and do not need to use tillage prior to planting soybeans. Soybeans are also good scavengers of nutrients and will be able to find adequate nutrients.

A big problem in late June and early July for planting soybeans in the upper Southeast is drought. No-till and minimum-tillage systems typically help hold moisture in the soil, hence a majority of growers have gone to these tillage practices.

“If we get really hot weather and no rain in late June, despite the yield loss from later planting, I would still wait for adequate moisture,” Wiatrak says.

“Under these hot, dry conditions the seed germination will be lower. There is a risk to waiting after July 1 to plant soybeans, because even under ideal conditions soybeans just don’t have the yield potential.”

How many seed to plant is also a major decision and one that directly affects the bottom line. Long-time North Carolina State University Soybean Specialist Jim Dunphy says in most cases less is better. Over the last five years, North Carolina soybean growers have been putting fewer seeds in the ground yet harvesting roughly the same amount of soybeans.

As a result of Dunphy’s pioneering efforts, it is estimated that North Carolina soybean growers saved over $25 million dollars in 2007 planting less seed, compared to the seeding practices recommended in the early 1990s.

Using funding from the North Carolina Soybean Growers Association, Dunphy says 96 on-farm tests of seeding rates were done across North Carolina between 2002 and 2005. Those tests compared seeding rates ranging from 25,000 seeds per acre to 200,000 seeds per acre.

The on-farm tests showed growers could cut the number of seeds they put in the ground roughly in half without diminishing yield.

Typically, Wiatrak says growers will increase seeding rate in soils with heavy residual matter on the surface by 10-15 percent to insure a better stand.

Making many of these management decisions now, will allow growers to get a jump start on soybean production. Too often double-crop beans are planted during critical production periods for corn, cotton and other crops, and by making decision now, growers can position themselves to make better crop of soybeans.


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