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Planting green in soybeans shows good results; more data needed

Tractor seeding into lush green cover crop
PLANT GREEN OR BROWN: A three-year study from Penn State shows many benefits from planting cash crops into living cover crops, but there are also many challenges.
3-year study shows the benefits and challenges of planting cash crops into growing cover.

Is “planting green” all it’s cracked up to be? Many farmers think the benefits — better conservation and soil health, better control of slugs — far outweigh the downfalls of this relatively new practice.

But what does the data say? A three-year study in southeast Pennsylvania provides at least some clues for farmers hoping to join the planting green crowd.

The study was done from 2015-17 on nine sites throughout central and southeast Pennsylvania. Heidi Reed, field and forage crops Extension educator for Penn State, says five of the sites evaluated soybeans while four evaluated corn. Cover crops used were rye and triticale.

Research method
The purpose of the study was to evaluate plots where cover crops were killed early to plots where farmers planted green about two weeks later.

“We had farmer cooperators pick a desired cash crop planting date for corn or soybeans and then we backtracked two weeks before,” Reed says. Roundup was used to kill the cover crops in the early plots.

There were four replications at each site. No neonicotinoid treatments were used in order to protect ground beetles and other beneficial insects.

The amount of cover crop grown varied by farm. At Penn State’s research farms, rye was grown at a much higher rate than the rest of the farms.

The farm sites were all long term no-till with cover crops. One site applied manure, she says, while two other sites did not.

“So, we really got a big picture of how planting green worked in central and southeast Pennsylvania,” she says.

Many farms used a roller crimper attached to the planter in the planted green plots, she says. At the university research farms, a ZRX Zone Roller with mini roller crimpers on each row unit was used.

The results
“One of the conclusions of this study is it’s not a one-size-fits-all thing. It’s very adaptable to different farms. That’s what’s making it so hard to get a fact sheet on it, because there are a lot of factors,” she says.

Delaying cover crop termination led to a doubling or tripling of biomass in most of the plots, she says. They also got better cover for conservation purposes and more carbon back in the soils.

But results varied by year and weather conditions. In 2015, a dry year, there wasn’t much difference between treatments. The residue even fizzled out about a month after planting.

In 2016, a year with “perfect” conditions, the residue lasted for most of the growing season. In 2017, a much wetter and colder spring, more biomass accumulated in the plots. Researchers also measured dryer soils when planting green than in the earlier plots, which supported the theory that later-growing covers pull moisture up from the ground.

“It was 2% to 7% dryer,” she says. “That small percentage in soil moisture, though, is the difference between mudding in the seed vs. having nice, crumbly soil to plant with less compaction.”

But having a thick cover also cooled the soil down, leading to delayed growth of the cash crop. In some corn plots tasseling was a week behind in the planting green treatments, leading to shorter corn.

“Soil was cooled between 1 and 4 degrees F depending on just how much biomass was actually there,” she says, adding that plant population in corn showed no improvement in the planting green plots.

One of the benefits of planting green is the ability to attract beneficial insects to control pesky slugs. But Reed says they saw mixed results. In 2016, for example, one site that was planted with a multispecies cover crop mix saw more slug damage than in plots with either rye or triticale, although she added that the multispecies plot also included radishes, which tend to attract more slugs.

The soybean plots saw no significant changes in slug damage, she says.

Better for soybeans than corn
One planting green corn plot saw a yield reduction of 10% while another saw a 5% yield reduction. Reed says only two corn plots showed a significant yield reduction, one of those being the plot with multispecies cover crops.

There was no difference in soybean yields.

“We found that with soybeans, there was no effect on our yield, but we also saw benefits with our soil armor, soil moisture management and a little help with the slug problem,” she says.

Heidi Reed, field and forage crops Extension educator with Penn StateSTART WITH SOYBEANS: Heidi Reed, field and forage crops Extension educator with Penn State, says prospective farmers should start planting green in soybeans before corn as the system is much more forgiving in soybeans.

Lower soybean populations were found in the planting green plots, but Reed says lower soybean populations aren’t a big deal since they can add on branches and pods throughout the growing season.

Corn yield can be limited by a lower population and lesser nitrogen. They used some crimson clover, a legume that fixates nitrogen, in some of the corn plots, but Reed says they saw no significant yield bump and actually had more pests to deal with.

More data needed
Many things weren’t measured in the plots, such as water infiltration, water-holding capacity and amount of organic matter.

“There are so many benefits that we didn’t measure that for many people are much more important for long-term profitability than a single year’s yield,” she says.

Still, Reed says some recommendations can be made. No more than 30 pounds of rye or triticale per acre should be grown unless planting late. Also, in a dry spring, it is recommended that covers are killed early so they don’t draw up too much soil moisture.

If you’re new to planting green, Reed suggests starting with soybeans before corn. She also suggests rolling taller cover crops as sunlight isn’t needed to start young seeds.

A drill can be more effective than a regular planter, especially in corn. She also recommends a nitrogen application at planting and an extra side-dressing later in the season.

If none of this works, talk to a farmer who’s had success.

“Plenty of growers in the area have done better than we did when it comes to planting green,” she says. “So, our suggestion is that you talk to them!”

TAGS: Soybeans Corn
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