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Cover crops gaining popularity with farmers

Sept. 6, 2013 | 0 comments


In many areas of Wisconsin today, cover crops are "cool."

Farmers are trying these secondary crops to prevent erosion, build soil nitrogen or produce an extra forage crop during the growing season. Sometimes all three can be accomplished.

Matt Ruark, with the University of Wisconsin-Madison Soil Science Department, said cover crops can build nitrogen if they are legumes or they can scavenge nitrogen and trap it in the soil profile – meaning the nutrient will stay put and will be there for the next crop in the rotation.

University research on cover crops includes plots at the 2,037-acre Arlington Agricultural Research Station on the Empire Prairie just north of DeForest as well as on farms in various parts of the state.

Ruark talked about the results of some of this ongoing research during the annual Arlington Agronomy Field Day, Aug. 28.

There’s growing evidence, he said, that there are many benefits from the use of cover crops.

In some cases the benefit is obvious – like protecting soil from erosion or a reduction in the need to purchase commercial nitrogen fertilizer.

But in other cases the benefits of a cover crop are less well understood scientifically.

"It’s almost like a bit of agronomic alchemy," he told Wisconsin State Farmer with a smile.

"There are some concepts related to crop rotation that aren’t well understood or documented by research."

Cover crops being used by farmers these days are generally radishes, grasses or legumes.

Legumes are popular after winter wheat. The nitrogen they can fix in the soil is of great benefit to the corn crop that will be next in the rotation.

The research is looking into some basic questions on cover crops, he said. "What will grow in Wisconsin? Will it prevent erosion? Will there be any extra benefits from it?"

Clovers, it is well known, will fix nitrogen and that can benefit the next crop planted, what agronomists call leaving a nitrogen credit.

A legume crop that can fix nitrogen reduces the cost of fertility for the crop that follows it.

In on-farm trials in Rock County, red clover (a perennial) was frost-seeded into a stand of winter wheat – broadcast onto the dry soils in March.

"The clover just kind of hangs out in the wheat stand until the harvest. We found a tremendous benefit from the nitrogen that the clover puts in the soil."

There was a 55-pound nitrogen credit that was available to the corn that followed the clover in that "rotation" but there is also an herbicide issue, he added, "because now you have a grass and a legume growing together."

Some of the farmers and crop consultants asked questions about that issue during the field day.

More research will have to be done on that part of the cover crop program.

In addition to its value in fixing nitrogen, clover has other attributes.

Clover, he said, has a tap root that works itself down into the soil profile doing a bit of what’s called "bio-tillage" in addition to fixing nitrogen. "It’s not as aggressive as radishes but it busts through some soil particles."

In the rotation that features perennial clover growing with winter wheat and then covering the field after the wheat is harvested, Ruark recommends that farmers consider killing it in the fall.

"That way there’s no timing problem in the spring. Sometimes weather or other field work in the spring means farmers can’t get the timing right to kill it off then."

The clover doesn’t provide as much soil cover as a cover crop of winter rye but it has the advantage of fixing nitrogen and if it gets a good start and grows aggressively it may be able to prevent some other weeds from taking hold.

Other clovers that can be used as cover crops – Berseem and Crimson clovers – will winterkill and die out before spring so that is another option for farmers to consider, he said.

In the trial that featured winter wheat and red clover followed by corn, Ruark said some fields produced over 200 bushels of corn.

"Corn is the logical crop to plant after the clover because it has the highest nitrogen need. In this trial we applied less N to get those yields."



Other trials are looking at the value of winter rye after corn silage.

Ruark said it’s a great cover crop to scavenge nitrogen and reduce erosion especially in corn silage fields where there is little or no crop residue left.

In fields where the rye was allowed to grow up and was harvested as forage, it held back tonnages on the corn that followed it.

"There’s concern that harvesting rye as forage holds back the corn and it never catches up."

But for farmers, this is a tradeoff they may be willing to make. He documented seven ton-per-acre harvests on rye silage and eight tons per acre of corn silage in one trial.

But, he added, the caveat on this research is that it documented what happened in 2012, a year featuring the worst drought in a generation.

For his money, Ruark said killing off the rye early is the best choice. That way it has served its purpose of preventing soil erosion and sopping up nitrogen, but it doesn’t get in the way of future corn yields.

"As early as you can be in the field - the minute you can get out there in the spring is when I recommend killing that rye cover crop."

In trials on farm fields in Rock, Sheboygan and Washington counties, Ruark said agronomists are looking at radishes following winter wheat.

"We want to find out how much N it’s sucking up. We’re also looking at how the use of cover crops like radishes may affect soil nematodes."

The research is also aimed at documenting what the use of various cover crops does to soil moisture, soil temperature and soil surface compaction.

"We want to look at what it’s really doing to the whole soil profile.

Some of the trials Ruark documented were supported by the Wisconsin Fertilizer Research Council, a group whose funding is derived from tonnage assessments on fertilizers and soil amendments sold in the state.

At the Arlington station, Ruark showed visitors some novel cover crops that are being experimented with, including sun hemp with radishes, sorghum-sudangrass and others.

More information on cover crops is available at the web site of the Midwest Cover Crops Council at www.mccc.msu.edu. There is a page on that site specifically dealing with each Midwestern state, including Wisconsin.


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