Review soybean production basics

Many farmers in the Southeast have grown soybeans in the past, but they haven't grown them in the recent past. All the more reason, says Auburn University Extension soybean specialist Dennis Delaney, that they review the production basics.

“In Alabama, we went from about 200,000 acres of soybeans down to about 150,000 acres when Asian soybean rust first hit. But we're gradually climbing back up,” says Delaney.

The limitation on soybean planting this year, particularly this year, has been the availability of seed, he adds. “Those high temperatures we experienced last year also were seen throughout the Midwest, killing the germination and the vigor of a lot of soybean seed grown under irrigation. Arkansas, Missouri and other states had 100-degree temperatures just as we did in 2007,” he says.

Growers who do plan on planting soybeans this year need to remember the basics, says Delaney. “These include soil testing and liming,” he says.

“Soybeans are very sensitive to low pH in the soil. Potentially, the rhizobia will fix the nitrogen for you. But if pH is too low, they just won't be able to do the job.”

In fields in which soybeans haven't been grown for awhile, Delaney says the standard recommendation is that growers inoculate. “This means if soybeans haven't been grown for two years or more. The new inoculants that are coming out are of a much higher efficiency than what may be in the soil — the native bacteria that has been there from year to year.

“But make sure the inoculant is soybean specific. Just like with all other legumes, there's a particular kind of rhizobia for soybeans. At $1.25 to $1.50 per acre, it's fairly cheap insurance compared to having to go back in and top-dress with expensive nitrogen, and a few farmers had to do that this past year,” he says.

Researchers looked at inoculants in three tests in Alabama last year, says Delaney, and two of those had not been in soybeans for five years. “Even where we didn't inoculate, there was no significant difference, so there was enough of the natural bacteria present in the soil. Again, it's pretty cheap insurance considering the price of nitrogen today,” he says.

There have been a lot of advertisements in farm publications about seed-applied insecticides such as Cruiser, he says.

“Some research has been conducted in the South on these insecticides. Basically, from what I've seen, we get a yield response to those only in the very early planted soybeans — such as Group IV beans planted in early April. If we plant in late April or into May, there probably will be no response,” says Delaney.

Soybeans, he says, are a very poor rotational crop if you're growing peanuts. The two crops share several diseases, including white mold and cylindrocladium black rot.

“We had a variety test in north Alabama where white mold came into soybeans following peanuts under irrigation. It came in at about the middle of July and killed about one-third of the field while stunting the remainder of the soybeans. We made about 30 to 35 bushels under irrigation.”

Nematode resistance, says Delaney, is another important consideration in soybean production, especially for root-knot nematodes. “Particularly as we get into the Group IV's, we find that we don't have a lot of resistance to nematodes. Most of the Group V's have some resistance, but it varies. Look at the charts from the seed companies and see where a variety falls in terms of resistance. You may want to move to a different field or try and find another variety. Very few varieties are resistant to reniform nematodes — there are just a handful, so watch out for that.”

A lot of disease resistance — to both foliar and soil-borne — can be “bought in the bag,” says Delaney.

He recommends that growers spread out their soybean maturities, from early to late, insuring that the beans are planted on time.

“If you have late-planted corn and you can't get it out on time, along with early soybeans, many times they'll be on top of one another in August. Corn may wait a little while, but these early planted Group IV soybeans will wait only a week or so.”

Like cotton, says Delaney, soybeans can be forgiving when it comes to plant populations. “Usually, about 150,000 plants is optimum. That gives a quick shading of the ground and translates to about 12 seed per foot on 36-inch rows and about 10 seed per foot on 30-inch rows. In tough conditions or when drilling or no-tilling beans, you can bump up that number.”

If farmers are fortunate enough to receive ample rainfall this year, they also are likely to see Asian soybean rust, he says. Alabama has about 25 sentinel plots located throughout the state, and these will be checked weekly during the production season, says Delaney.

“If we do get a wet, rainy summer, our research over the years has shown an average yield increase of about six bushels per acre whenever we use one of the new fungicides like Headline and Stratego, even if we don't have heavy disease pressure.”

Soybeans, says the agronomist, don't respond well to deep tillage. “If you plant after wheat and you've subsoiled or deep-tilled the wheat, just drop and no-till plant soybeans. There's no need in losing that moisture and straw.”

Traditionally, Alabama growers have planted Group V soybeans in the northern part of the state, Groups V and IV in the central region, and Groups VI and VII in the south, says Delaney.

“Over the years, we've moved to an earlier maturity group throughout the state.

“Normally, we planted from May through mid-June after we had done everything else and we tried to harvest in September and October. In the last few years, the Group IV Early Soybean Production System (ESPS) has been used by some growers. With each planting system, there's different management with different pest problems for each one. With ESPS, we're trying to move it back to earlier in the year.

“This system shifts Group IV planting to mid-April, and then you have seed fill in July and maybe early August. Before we run out of moisture, we get them out in mid August.

“ Normally, there's a lot less worm pressure with this system, but you need to watch for stinkbugs. In 2005, some growers saved themselves one fungicide spray with the early production system.”

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