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Pioneer: Controlling plant growth in high-yield soybeans

In 2006, Kip Cullers grew 130-bushel soybeans. That gaudy number was followed in 2007 with a yield of over 154 bushels.

To accomplish such yields, Cullers starts with proper variety selection.

“Not only does he want a variety that yields high, but one that can take the kind of management he puts them in and still stand,” said Greg Luce, at the recent field day at Cullers' Stark City, Mo., farm. “That's a challenge.”

Luce, a Pioneer area agronomist in Missouri, picked up a container of soil and showed it to those on the tour.

“This soil I got from a research field around Miami, Mo. It's very black and, for Missouri, has pretty high organic matter. It's a very productive silt loam.”

Luce then picked up shovel full of paler soil.

“This is Kip's soil and the color is different. A lot of people think, ‘Hey, how are these record yields coming from down here in southwest Missouri?’ We're not very far from Branson.

“But the soil is more productive than you'd think. It was formed in prairie vegetation and even in rather wet conditions, it'll crumble up. It has a deep profile and drains well. That's important considering the amount of water Kip is putting on his beans.”

Cullers also utilizes poultry litter.

“The county we're in, Newton, has the highest agricultural income of any in the state. That's largely because of poultry production and Kip makes use of readily available poultry litter. His fertility levels have been built up to a good base level.”

Cullers treats his soybeans much like the green beans he grows. He waters the crops regularly — low water volume, but frequent irrigations.

“He also protects the plant in several ways. He adds optimized seed treatments to increase nodulation and also uses insecticide and fungicide seed treatments.”

By doing all this, “Kip grows big plant factories — big tall beans. That can create some real challenges.”

Because of the things Cullers is doing fertility-wise and to protect his plants, “they grow continuously,” said Scott Dickey, a Pioneer area agronomist based in Odessa, Mo. Even some of the determinate soybeans in trials are continuing to bloom and grow.

“When we started doing (yield) contest beans here a couple of years ago, Kip had about 300,000 plants per acre. Those populations have been dropped down a bit in an attempt to reduce lodging. Having that many plants in a small area, they tend to want to grow up for light. They're competitive for light.”

By reducing the populations, shorter plants are produced that tend to bush more.

“We have switched to twin-row for the contest fields. By maintaining that, we're still getting light penetration later into the season. That helps out before they lap over and cover the rows. “We'll see how that works versus, say, a drilled, equal population.

“We'll probably drop down closer to 200,000 plants per acre hoping to squat-down the plants a bit more.”

Typically, the researchers find a larger diameter stem at a lower population with a few more branches. However, on Cullers' operation, “even under the higher populations, the stems are still about thumb-sized. So, I don't know if that will do us a lot of good. We're trying to think about other alternatives to get the plants to squat down.”

Dickey pointed at an adjacent soybean plot. “That's what we're looking at here. On this side, we've done several plant hormone and herbicide treatments to try and stop the main bud in the plant — either by stopping it from growing (basically killing it) or cutting it out. By taking those out, you allow for a bushier plant.”

Luce held up several plants he'd pulled. “What I have here are some plants we've trimmed rather low to the ground. You can see the ends that have been clipped. We just took a battery-powered hedge trimmer and trimmed the tops out. That isn't practical on lots of acres.”

But typically, on plant populations like Cullers' “there will be one main stem. By cutting that out, the plant branches all over.

“The goal has been achieved. However, we cut the plants way too late. We need to be cutting the tops out at V-5, V-6, so there are two or three nodes to branch out from. If we cut them too low, we'll kill them.”

As for plant hormones, “Apogee is used in apple crops,” said Luce. “The cotton version is Pentia. The products keep the plant from growing so much. We applied those, as well as Cobra, at 2X and 1X rates. I'm more of a fan of the ‘burners’ than the plant growth regulators.”

Dickey prefers those that are contact only. “Those whack the plant and then it recovers. If you get the wrong rate with the plant growth regulators and hormones, the effects can be too long lasting.

“That's why, for the contest, we're leaning more towards the clippers. Just take a hedge trimmer out, cut the tops out and let them go. The damage is quick and there isn't a lasting effect.”

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