Challenges of No-Till Organic Corn Can Be Overcome

3/23/2013 7:00 AM
By Chris Torres Staff Writer

It’s no secret Roundup Ready corn has been good for the advent of no-till farming.

You can spray the herbicide right on the plant and not worry about its potential negative effects, effectively eliminating the need for tillage.

And while the overall adoption of no-till has continued — more than 50 percent of Pennsylvania’s fields are no-till — you likely won’t see much of that adoption in organic fields.

But Steven Mirsky, a research ecologist with the USDA’s Agricultural Research Service and Hanna Poffenbarger, a graduate assistant at the University of Maryland, think widespread adoption of organic no-till corn could be a reality with some different approaches.

The two talked about optimizing weed suppression and nutrient use in organic no-till corn during a webinar Monday.

With the demand for organic corn outstripping supply and organic feed shortages becoming chronic, growing organic no-till corn could open up an attractive market for certain producers, Mirsky said.

“A lot of those producers are also soil-conservation minded and are very concerned about returning to tilled systems,” Mirsky said. “So if we can develop reduced tillage or no-till, this might be a way to increase production.”

Growing organic no-till corn comes with many challenges. Not only are the weeds difficult to deal with since there aren’t many spray options that organic growers can turn to, the tight window of killing an overwintering cover crop, planting corn and making sure corn gets the nitrogen it needs are also significant challenges.

Mirsky said one way of possibly reducing weed pressures in organic no-till corn is including a perennial grass cover crop, such as perennial ryegrass, in the traditional three-year organic corn crop rotation.

Hairy vetch is a popular choice for producers wanting plenty of nitrogen for their corn, since it can fixate nitrogen itself. But that also creates a hardy environment for weeds, he said.

Mirsky said mixing or even replacing hairy vetch with ryegrass can help control weeds come spring, since the crop can literally get rolled down using a roller crimper machine, leaving behind a weed suppressing mulch that a grower can plant corn right into.

Poffenbarger said cover crop mixtures generally add between 7,000 and 8,000 pounds of biomass per acre.

“In general, adding some grass along with vetch did increase biomass production,” she said.

The decomposition and persistence of a cover crop in corn, she said, can also play a factor in weed suppression during the season.

In a study she did last June, Poffenbarger measured the amount of weed emergence in fields planted with either a rye cover crop, hairy vetch cover crop or 50/50 mix of the two.

The first samples were taken in early June, which showed the amount of weeds pretty consistent across all three systems. But as time went on, weeds increased more dramatically in the straight vetch planting compared with the rye and mix plantings, Poffenbarger said.

She and Mirsky also looked at nitrogen content and the timing of its release for corn.

Corn nitrogen uptake is most critical at sidedress all the way to silking, which usually occurs in early July.

In general, and probably not surprising, hairy vetch releases more nitrogen and has more available for corn than the rye or 50/50 mix, especially in a tillage system, when residue is turned under ground for the corn to uptake.

In a no-till system, nitrogen release is delayed, mostly because the residue is on the surface and drying, and wetting of the cover-crop residue leads to slower decomposition, Mirsky said.

He said the delay was most pronounced in the rye and mixed systems, which he actually supplemented with poultry litter to get the amount of nitrogen the corn needed for good growth.

“Once you get to sidedress, that’s when corn is really taking its nitrogen,” he said.

The minimum amount of poultry litter needed was 1.5 tons per acre to get a respectable corn yield, he said. Poultry litter adds more costs since the litter has to be trucked in. Mirsky also said you don’t want to add too much litter since it could result in too much phosphorus being applied.

As far as impacts on yield, Mirsky said vetch alone will result in a higher yield, but again the weed issues are the main problem. Once you add a grass, nitrogen has to be applied to get growth.

“We could pretty much get away with adding only 1.5 tons of poultry litter per acre,” he said.


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