FOR HIGH YIELDS corn and soybean plants need to get as much light as possible into the canopy during critical growth periods

FOR HIGH YIELDS, corn and soybean plants need to get as much light as possible into the canopy during critical growth periods.

Sunlight is a major key to high corn, soybean yields

If a farmer can get light to the bottom of the canopy during critical grain fill, he can increase seed weight and you can increase yield significantly. Soybean plants can store sugar from photosynthesis for later use. Future efforts to increase and sustain grain crop yields in the Southeast must include a good pest management program.

When David Hula grew 429 bushels of corn per acre on a small contest plot near Charles City, Va., he made international news and created a nationwide quest to find out how he did it.

Likewise, Kip Culler in Missouri set off a chain reaction of research when he recorded a record 161 bushels of soybeans per acre. 

Since those lofty yield records, farmers, university researchers and industry scientists have been on a quest to figure out how to consistently produce these ultra-high yields.

One of those in the hunt is North Carolina State University Extension Specialist Ronnie Heiniger.

Last year, Heiniger planted a test he called, appropriately, Hula 400. His quest to grow 400 bushels per acre corn fell a bit short, despite using an expensive array of chemicals that he called The Cadillac Treatment.

Despite failing to notch 400 bushels per acre, the North Carolina State scientist did manage to average better than 300 bushels per acre across the large test site, including many plots that had much less expensive treatments than the Cadillac Treatment.

From a practical standpoint the 2012 Hula 400 tests at the Northeast Ag Expo were a big success. Growers got some good insights on how to grow 300 bushel per acre corn.

But, the 400 bushels per acre eluded the North Carolina State researchers, much as it has eluded others in the Midwest.

At the 2013 Northeast Ag Expo, Heiniger tried his hand at producing ultra-high soybean yields, working with North Carolina State Soybean Specialist Jim Dunphy.  

As with the Hula 400 tests, the North Carolina State researchers got good results, but don’t expect record breaking yields in soybean tests this year.

How to grow 400 bushels of corn, 100 bushels of soybeans per acre?

So, what does it take to grow 400 bushels of corn and 100 bushels of soybeans per acre in North Carolina?

“It’s all about light. If you can get light to the bottom of the canopy, especially during critical grain fill periods of growth in corn or soybeans, you can increase seed weight and you can increase yield significantly,” he says

He adds that one reason Kip Cullers is able to consistently grow 100 bushel per acre soybeans is that he knocks out the center bud of the soybean plant.

His soybean plants don’t get so tall and more sunlight filters down through the plant and builds seed weight. He also plants on twin rows, which also allows more light between the rows.

Getting the right amount of light isn’t nearly as easy as it may sound. In two years of testing, Heiniger’s research team has found more things not to do, than things to do to maximize light and to increase seed weight and overall yield.

Joe Oakes, a graduate assistant working with Heiniger, is finishing a two-year test in which he used different techniques to try and maximize light filtration through the canopy of soybeans.

“We know that the R3 and R4 growth stages are critical in seed set, and by R5, the plant begins getting seed into the pod. So, we focused our work on the R5 stage, “ Oakes says.

In one test he looked at high soybean plant populations and defoliated a percentage of the plants. The end result was to slow photosynthesis, reduce seed weight and ultimately hurt yields, more than helping.

He also tried shading soybean plants to simulate a loss of foliage. By shading plants from R1 through R5 growth stages, he didn’t adversely affect yield, but he didn’t stimulate seed weight nor increase yields.

However, by shading soybean plants from R5 until maturity, he again restricted photosynthesis and reduced seed weight and yield.

His research did show an increase in pod weight when he went into his test plots and removed soybean plants to get down to a plant per acre rate of 20,000.

However, the increased seed weight did not compensate for loss of plants and ultimately, this plot proved to be one of the lower yielding in the tests.

Soybean test plots at this year’s Northeast Ag Expo were harvested in late October and complete data will be available at winter grower production meetings.

Can we get plant populations up and still build seed weight?

The obvious question, Heiniger points out, is can we get plant populations up and still build seed weight?

The answer is yes, he says.

Soybean plants have the capability to translocate carbons and don’t have to depend solely on nutrients fixed by leaves during the R1 through R5 growth stages. Soybean plants can store sugar from photosynthesis for later use.

“Ideally, we want all the sugar possible to go to the seed to produce higher seed weights. To get this extra energy to the plant, we have to find a way to store sugar, in the form of starch, then get it to the plant when it gets to the R4 to R5 stage and begins pod development,” Heiniger says.

To get consistently high yields, whether it be in corn or soybeans, early growth is important to set the stage for translocation of nutrients to seed development.

And, getting as much light into the canopy during these critical growth periods is essential to improving yields, the North Carolina State researcher adds.

It appears it will be critical to begin fixing and storing sugars before the R1 growth stage. By increasing leaf surface early in the season, it can produce more than is needed by the plant. It can then store it for future use at the R1-R5 seed development stage of growth.

Light is the key, Heiniger says.

“One of the problems with getting adequate light into the canopy of grain crops is the tendency to grow big plants.

“In many cases bigger is not better when it comes to high yielding grain crops. Obviously, if plants get too tall and/or foliage is too dense to allow light penetration, there will be limitations on how much the plant can build seed weight and thus produce ultra-high yields.”

There are other limiting factors to grain yields.

Insects are a significant factor. Damage from insects or diseases can damage foliage and significantly impact seed weight in a negative way. 

Clearly, Heiniger says, future efforts to increase and sustain grain crop yields in the Southeast must include a good pest management program.

Some of the strobilurin fungicides labeled for use on corn and soybeans have shown some capabilities to increase photosynthesis.

Finding the optimum use for fungicides on soybeans is an ongoing hot research topic for researchers across the country.

North Carolina typically produces about 1.5 million acres of soybeans annually. Last year growers set a statewide yield record of 39 bushels per acre.

The 2013 crop has been plagued by historic rainfall and was planted a month to six weeks late, especially double-crop beans that make up about half the state’s acreage.

Yields will likely take a big hit from the prolonged cool, wet weather, but the future is bright.

“We are getting translocation of sugars in our soybeans in North Carolina, which means we do have a means of building seed weights and to produce ultra-high yields of soybeans comparable to those being grown by Kip Cullers in Missouri,” Heiniger says.

TAGS: Soybeans
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