Plant Cover Crops

Learning about the benefits of planting cover crops.

Nitrogen from Cover Crops

Benefits of a Pure Stand of Cover Crop Red Clover

December 28, 2020

by Dustin Johnson

I recently plowed under a successful stand of red clover in an organic wheat field on my farm near Kokomo, Indiana. I have grown alfalfa and mixed stands of hay as a cash crop for my entire career. Five years ago we began experimenting with organic grain production to try something new and take advantage of the synergies between organic grain farming and our existing hay business.

This was my first experience growing a pure stand of red clover. The main goal for the stand was nitrogen fixation for next year’s organic corn crop.

Along the way, I also gained a forage harvest, weed suppression, and soil health benefits. Please read further for a more in-depth discussion of my experience and the benefits that this time-proven practice can bring to your farm.

FROST SEEDING

On February 21st, I broadcasted 15 lbs/acre of red clover seed into my dormant wheat field. Frost seeding should take place near the end of winter when a period of nightly freezing and thawing is anticipated. The ground was frozen enough to hold up the tractor and the field contained a light dusting of snow. This helped me see the spread pattern of the clover seed.

Red clover is my personal first-choice when frost seeding: The seed is relatively inexpensive, clover can thrive underneath a crop canopy, it can be harvested for dry hay, and it works! Red clover seeds are heavy and round with a high level of seedling vigor. They naturally sort through material on top of the soil and fall into the “honeycomb” of soil cracks created by frost. This is the same process by which red clover stands naturally persist on road sides and barn lots.

If grazing is your primary goal, plant an improved species such as Bearcat or Gallant. White and berseem clover can also be successfully frost seeded for forage use. If you plan to exclusively grow it as a cover crop, sweetclover and mammoth red clover are also good choices.

Around the time my wheat broke dormancy, the red clover seedlings emerged. The frost seeded clover scavenged sunlight that filtered through the rows of wheat, but grew more slowly than the wheat and stayed beneath the wheat canopy. The presence of red clover in the wheat field did not interfere with the wheat’s ability to grow or be harvested. From the road, the wheat looked like a normal wheat field. Only after harvest was a carpet of green growing clover revealed.

FORAGE HARVEST

Once the wheat was harvested and the canopy opened to the red clover, it grew very quickly. I mowed the red clover for hay about a month after wheat harvest on August 19th. The clover was nearing full-bloom and the weather was right. The hay was mostly red clover, but also contained a few weeds and about 4” of wheat stubble. This medium-quality hay was the most fragrant, sweet-smelling hay that I have ever baled! Yield was also impressive: 2.3 dry tons/acre in a single harvest. Even priced modestly, this hay harvest was a significant boost to the profitability of my wheat crop.

COVER CROP VALUE

After taking a cutting of hay in August, I let the summer regrowth accumulate for a green manure to plow down. The regrowth was vigorous and thick. Weeds that had been present in the growing wheat were mowed before going to seed by the wheat and hay harvests. Newly germinated weeds could not compete with the established red clover. This certified organic field was nearly weed-free in late summer.

The clover bloomed again in September and was a haven for wildlife and pollinators.

In early December, I moldboard plowed this land and the red clover again showed its value. The clover was still actively growing and removing water from the soil. Areas of the field that did not have a good stand of clover were noticeably wetter. The clover taproots penetrated the plowing depth and prevented the wetter clay soils from “slabbing.” The pictures below show the loose friable soil created by the clover roots compared to an area of shallow-rooted grass sod plowed at the field edge.

Note the difference in the above plowed soil (with clover) vs. the soil below (no clover).

Those same roots will provide a soil health benefit below the plow layer as well. The clover taproots penetrated the soil much deeper than the plowing depth. The roots will help prevent a plow pan from holding water when they decompose this winter and drainage occurs in the old root channels.

The red clover has now begun to decompose within the soil profile and will be releasing nitrogen for my organic corn crop next spring. University sources estimate that a successful stand of red clover that is terminated after blooming can release 70 to 120 lbs of N per acre.

Now is the time to make preparations for frost seeding clover on your farm. Whether your goal is nitrogen fixation, improved pasture quality, or soil health, frost seeding clover this winter is an easy and cost-effective way to achieve big results.

Cover Crops in Wisconsin – Full Speed Ahead!

This cover crop field was ready for harvest in late September 2012.

I took a new management position in May of 2012 with Wisconsin based Legacy Seeds, Inc.

While my main responsibility lies in working with alfalfa and forages I also was pleased to find out that there were several folks in Wisconsin that were using cover crops!  Well, you would figure that I’d get involved more with cover crops in the Badger state, and I have.

Wisconsin Cover Crop Meetings

In February 2012 I conducted two cover crops meetings in the Fox Lake, WI area with over 75 producers present. The purpose of these meetings were to teach farmers about how cover crops can work in their farming operations.  I was very pleased with the outcome of those meetings as over 10,000 acres were planted on farms that were represented at those meetings.

In July I held three more cover crop meetings in Eau Claire, Waupaca, and Brillion, WI. All combined, there were over 150 farmers present and I’m confident that there were at least 30,000 acres of cover crops planted by those farmers.

While I don’t have figures of how many cover crops were planted in Wisconsin, I think there were as many as 250,000. Many of those acres were after wheat was harvested and a surprising number after corn and soybeans.

Cover Crops for Forage & Manure Management

Feed was one reason so many acres were planted. The severe drought has created a forage shortage.

But many farmers planted their cover crops because they want healthier soils and better production.  Still others planted because they want to hold onto the nutrients from their manure.  Whatever the reason, cover cropping is alive and well in Wisconsin – and growing.

You can click on the pictures below to see a larger image of each.

The Oats, Appin Turnip and Cowpea combination should make excellent haylage for the Wisconsin dairy market.

The nodules on the Austrian Winter Peas were multiple and large. This field will be planted to corn next year and it sure appears that a good amount of nitrogen will be in the soil and available for that corn crop.

This field of Austrian Winter Peas and Radish east of Green Bay, WI was planted after wheat in severe drought conditions. Thankfully some later rains came to get the mixture up and going.

Inoculating Cover Crop Legumes Pays Off

Several farmers have asked me why they need to spend an “extra” 4-6 cents per pound to inoculate the legume seed they are planting for producing nitrogen with their cover crops.  I get asked this especially about Austrian Winter Peas and Cowpea.

However, if you are planting Crimson Clover, Berseem Clover, Kura Clover, Alsike, Hairy Vetch, Sunn Hemp, or Medium Red Clover it’s just as important inoculate!  Why?  I’ll list a few reasons below:Inoculated peas are significantly better at producing nitrogen

  • Legumes are planted as cover crops most specifically to produce nitrogen.
  • Legume seed is relatively expensive; if it does NOT produce nitrogen, then it is exceptionally expensive.
  • The inoculant is a species specific bacteria that allows that plant to fix nitrogen.  If there are not enough bacteria there is limited nitrogen production from the legume plants.
  • A healthy legume cover crop can produce nearly 200 units of nitrogen
  • Even if you have produced a similar crop in your field within a two year time period, it still pays to inoculate each year since many of the bacteria prove to be “weak” and unable to perform like a healthy and vigorous bacteria.
  • If inoculating Peas or Cowpea you will need to do a “seedbox” treatment.  There are not yet inoculants that can be pre-applied that will allow you to have healthy bacteria. Therefore, most inoculant companies suggest putting the inoculant on within hours of putting the seed in the ground.

Be sure to get very good coverage on all of the seeds.

Do not hurry. Each seed needs coverage to actually be inoculated. I know that sounds silly, but I have seen many fields and plots where only some of the pea or vetch  plants were performing well.  The ones that looked poor had no nodules.

Many companies sell pre-inoculated clover seed.  If yours does not, then either find another supplier or purchase the correct inoculant from your current seed supplier.  Do not waste a great opportunity to produce as much nitrogen as possible. It is  less expensive to produce nitrogen than it is to purchase it.

A well inoculate Austrian Winter Pea nodule will be pink inside like the one above.

This photo shows a mixture of well inoculated and poorly inoculated Austrian Winter Pea plants. It is important to inoculate each seed with the nitrogen fixing bacteria.

 

 

Cover Crops in the Great Plains – a view from a long time cover crop user- Part 2

In this cover crop post I again quote Paul Conway from Kansas, who is giving his input on cover crops in the Great Plains. In this article, Paul shares his experience with Austrian winter peas, field peas, chickling vetch, and hairy vetch.

Dave,

Austrian Winter Peas: I have limited and disappointing experience with Austrian Winter Peas.  They always winter kill and they must be planted at an inconvenient time.  It seems that the areas where they do well do not follow a simple geographical line.  Austrian Winter Peas do very well about 60 miles south of me in central and southern Kansas.  Ironically, they seem to do fine in the Nebraska panhandle, which is much colder than we are. I think consistent snow cover makes the difference.

Field Peas: also know as Canadian field peas or forage peas. I’ve grown these in early fall with oats and forage radish. I don’t know how much nitrogen they fix but they do winterkill by early winter –  mine haven’t died yet – probably consistent lows in the middle teens will do it.

I also plant them in early spring the same time as oats, killing them for June planted cash crops.  Mowing after flowering will effectively kill peas.  Where peas shine is in mixes and in cool climates.

The pea/oat or pea/triticale is excellent for haylage or silage. These mixes have the same benefits for livestock farmers as the soybean/summer grass mixes.

In much of the Midwest and east, double cropping is possible, oat/peas followed by soybean/milo or sorghum-sudan.  Further north, the oat/pea mixes would mature too late.  In that regard, I think that field peas could be managed as a summer annual (like soybeans) in the Great Lakes states, upstate New York, Pennsylvania, and New England.

Peas can handle routine summer temperatures in the low-mid 80s. Peas can be grazed. Peas aren’t shade tolerant so they don’t do well when sown into row crops.  Frankly outside the mixes I think the clovers may be more versatile.

Chickling Vetch: Also known as “AC Greenfix.” It will fix nitrogen faster both in the fall (it winterkills about the same time as the peas) and in the spring.  AC Greenfix seed is more expensive and harder to plant due to it’s shape.

Hairy Vetch: As you know, hairy vetch is the strongest nitrogen fixer among the annuals.  Hairy vetch easily fits into vegetable rotations. I have seen two foot vine growth and numerous fat nodules on vetch in early-mid April after a mildly wet fall and an early spring.  It will be harder to fit into field crop rotations, especially corn-soybeans.

Here the optimum time to plant hairy vetch is September, but it can be planted as late as mid October.  It needs minimal soil contact which isn’t a problem in a normal fall. A dry September/October, like I had this year, is a problem.

I know that you have some experience with flying in hairy vetch into maturing corn or soybeans.  Another option is to plant it very late (mid-late November) and hope it doesn’t germinate until the soil warms up in late winter-early spring.   I don’t think people realize how versatile hairy vetch can be.  In the northern areas suited for field peas (see above) hairy vetch could be managed as a summer annual. [I have seen hairy vetch flower, drop seed which stays dormant during a hot dry summer – Dave’s EMPHASIS HERE – this is why I caution growers about Hairy Vetch.]  When the weather cools down in late August the vetch seed sprouts.  It is still warm then through September and early October with temperatures similiar to the Great Lakes states and New England in the summer.  So why couldn’t vetch be planted in early summer in these areas?

Years ago I planted hairy vetch in April between wide rows of vegetables just to see what would happen.  I remember lots of growth by July, despite a hot dry summer. The soil under the vetch was cool and moist.  The vetch did not grow enough to fix much nitrogen by May but it may have fixed enough nitrogen for mid-summer planted crops.

In 2012 I will plant hairy vetch and other vetches (purple) in the spring and record how they do.

Finally, new cultivars of hairy vetch come out which may have promise.  I will try a new variety called Purple Bounty, which is supposed to mature two weeks earlier but with less winter hardiness.

 

Nutrient Scavenging Cover Crops – How much good are they doing? It depends.

Meet the Cover Crop Scavengers

Over the years I have worked with cover crops I have recommended that producers use “scavengers” like Annual Ryegrass, turnips, cereal rye,  winter barley, oats,  and cover crop radishes.  These cover crops do a very good job of capturing excess nitrogen and other nutrients and keeping them from reaching the ground water or running off with surface water.  When the nutrients are scavenged they are available for the subsequent crop.

Most of these scavengers are “luxury consumers” of nitrogen and a few of them are also “luxury consumers” of phosphorous.  These are ideal to use on land where manure is applied.  They also work very well when grown with a legume like crimson clover, hairy vetch, chickling vetch, and Austrian winter peas.

However, if  limited amounts of nitrogen are available how will these scavengers perform?

The answer: not as well.

My answer is subjective but based on observations that I will show you via some photos.

 

Observation 1

It is easy to see where the manure was knifed in in this field. But how much more N is being taken up where it is darker green? We'll be doing tissue tests soon to determine that.

The first observation is where hog manure was knifed in after wheat had been harvested. The photo shows that the cover crop (Annual ryegrass and Appin turnips) looks considerably darker where the manure had been applied.  We will soon be taking tissue samples to see what difference there is in the amount of N, P, and K are in the plants.  We also anticipate a future post showing a root pit view of the root growth difference (if any).
 
 
 
 

Observation 2

The "yellow" strips are pretty obvious in the cover crops in this seed corn field. It is not obvious where the corn rows were but I expect the lighter strips are above where the corn row had been.

The next observation comes from a seed corn field in north western Indiana near Demotte in Jasper county.  The main area of difference in N uptake is found where the male corn rows had been cut out this summer after the female rows had pollinated.  The difference is color was not as dramatic as it was in the previous situation but there was a clear difference in color and the amount of growth (considerably more developed) of the cover crop.
 
 
 
 

Observation 3

The left half of this photo had 35#/acre of N but had no legume to feed the radish. The right half of the photo shows the significant color and growth difference when radishes are grown with crimson clover (and the 35# N/acre).

The next field is near Edgerton in NW Ohio.  This field had three different applications being trialed.  One area had a crimson clover and GroundHog radish mixture, another area had an Austrian Winter Pea and GroundHog Radish mixture.  In between these mixtures was a strip of Tillage cover crop radishes with no legume but with around 35 units of nitrogen applied (the ~35 # of N was applied across the whole field).  If you attend many cover crop meetings you will hear speakers tell you to apply 35-50 units of N on radishes if they are sown without a legume or without manure applied.  After seeing this field I believe we are underestimating what kind of N we need to apply for “best” results as the radish only strip had considerably smaller radishes with much less tuber growth and more “yellow leaf”.    The area with the crimson clover/GroundHog Radish Mix was by far the darkest green and had the largest radish growth.  However, even though the peas did not look as impressive as the crimson clover, the radish growth was significant and much darker green than the radish area grown without any legume.

Observation 4

Not only does the crimson clover add nitrogen to the soil it also greatly enhances the soil structure. The soil on the left came from where there was only radishes planted. The soil on the right had crimson clover and radishes mixed together.

Another observation from this field was that where the radishes were grown with the crimson clover the soil had a much improved structure over the soil where only radishes were grown.  The massive amounts of crimson clover roots (with an exceptional amount of nodules on them by the way) gave the soil a much better texture.  See a very descriptive video here.  These soils are “Williams County Clays” or “NW Ohio clays” and are well known for their tightness and poor drainage.  As the farmer Ryan Sanders said after seeing the results of this experiment… “I will never plant radishes alone again.”

 

Photo diary- Corn after a cover crop (after corn)

“Planting this corn field was like planting into a garden” said my friend Dave.   He has been a ‘cover cropper” for six years now.  This year Dave no-tilled approximately 50% of his acres.  Dave is one of the most innovative guys I know…but he’s also “cautious”; he does not want to lose money!  That’s why Dave loves cover crops…using cover crops he has improved his profitability.  In this photo diary we will look at photos from April, May and June where Dave had a cover crop consisting of Oats/GroundHog Cover Crop Radish/AU Robin Crimson Clover.  The previous crop was corn.

An April view of the field with the AU Robin Crimson clover that over wintered. The oats and GroundHog Radishes had died out over the winter as expected.

 

A May photo of Crimson Clover that could not be killed yet because the field (and all other fields in the area) was too wet to spray. Normally by the date the photo was taken the Crimson Clover would have been dead and the corn would have been planted.

 

No-Till Corn on Corn planted into Oats and AU Robin Crimmson Clover

Medium Red Clover as a cover crop

Medium Red Clover frost seeded into wheat provides good nitrogen production and excellent forage/green manure.

Frost seeding clover into wheat has been a standard practice for many years.  Many producers have used “60/40 Plowdown Clover” in their wheat…but in many areas that practice has stopped as double crop soybean plantings have pushed further into northern Ohio, Indiana, and Illinois.  If double crop soybeans are not an option (or not desired) then a great choice for a cover crop in 2011 is Medium Red Clover.  While the 60/40 Mixture generally included 60% Mammoth Red Clover and 40% Yellow Blossom Sweetclover it seems more economical to use VNS Medium Red Clover because of the pricing of the seed this winter.  Be sure to use a pre-inoculated seed when sowing into your wheat so you get much improved clover production and N production.

Below are the advantages and disadvantages of using Medium Red Clover as a cover crop.  (This cover crop will pretty much be used in wheat acres.)

Advantages:

Advantages

  • Produces 75-100# N
  • Good root system-soil builder
  • Easy to frost seed into wheat
  • Often least cost cover crop
  • Easily killed
  • Excellent for forage

Disadvantages:

  • May get too tall in wheat and affect harvest

“Where is my nitrogen?”

Austrian Winter Peas add as much as 100 untis of nitrogen to the soil if they hav egood growth in a good stand.

This question keeps coming up on a regular basis in cover crop meetings….”where is my nitrogen?”

There are a number of things we know:

  • Legumes produce N and some of that N is available for the next crop.
  • Most cover crops scavenge N.  Some of that N is available for the next crop.
  • Some of the N is not available for the next crop.

How do you determine how much N is available for the next crop?

According to Managing Cover Crops Profitably: (p. 22)

 How Nitrogen is Released

How much N will soil really acquire from a legume cover crop? Let’s take it from the point of a freshly killed, annual legume, cut down in its prime at mid-bloom.The management and climatic events following the death of that legume will greatly affect the amount and timing of N release from the legume to the soil. Most soil bacteria will feast on and rapidly decompose green manures such as annual legumes, which contain many simple sugars and proteins as energy sources. Soil bacteria love to party and when there is lots to eat, they do something that no party guest you’ve ever invited can do—they reproduce themselves, rapidly and repeatedly,doubling their population in as little as seven days under field conditions (306). Even a relatively inactive soil can come to life quickly with addition of a delectable green manure. The result can be a very rapid and large release of nitrate into the soil within a week of the green manure’s demise. This N release is more rapid when covers are plowed down than when left on the surface. As much as 140 lb. N/A has been measured 7 to 10 days after plowdown of hairy vetch (363).Green manures that are less proteinrich (N-rich) will take longer to release N. Those that are old and fibrous or woody are generally left for hard-working but somewhat sluggish fungi to convert slowly to humus over the years, gradually releasing small amounts of nutrients. Other factors contribute significantly to how quickly a green manure releases its N.Weather has a huge influence.The soil organisms responsible for decomposition work best at warm temperatures and are less energetic during cool spring months. Soil moisture also has a dramatic effect. Research shows that soil microbial activity peaks when 60 percent of the soil pores are filled with water, and declines significantly when moisture levels are higher or lower (244).This 60 percent water-filled pore space roughly corresponds to field capacity, or the amount of water left in the soil when it is allowed to drain for 24 hours after
a good soaking rain. Microbes are sensitive to soil chemistry as well. Most soil bacteria need a pH of between 6 and 8 to perform at peak; fungi (the slow decomposers) are still active at very low pH.Soil microorganisms also need most of the same nutrients that plants require, so low-fertility soils support smaller populations of primary  decomposers, compared with high-fertility soils.Don’t expect N-release rates or fertilizer replacement values for a given cover crop to be identical in fields of different fertility. Many of these environmental factors are out of your direct control in the near term.Management factors such as fertilization, liming and tillage, however, also influence production and availability of legume N.

So while know that cover crop legumes produce nitrogen we also know that the nitrogen will be released at different times and in different amounts according to the circumstances in individual fields and with different management practices.

In 2010 many producers across the Midwest  shared that they could see a “big difference” in their corn yield where they had a legumes as a cover crop.  While we cannot easily (or maybe not totally) quantify the pounds of N available for the next crop we can count on some level of improved performance.  Can we reduce our inputs?  Maybe.  Can we always get higher yields?  No.  Can we anticipate an improved yield?  Probably.  Some folks will tell you “yes” to those questions!  Some others will have a different experience.

So what do you do?  Plan for success, scout your corn, use a pop-up and/or starter with nitrogen…and scout…oh, yeah, I guess I already said that!

Cover Crop plots in December-What can we tell now? part 2

In this post we look at two more videos of mixes on December 2, 2010.  This first mix in this session is of Austrian Winter Peas and GroundHog Radishes.  The seeding rate is 30# Peas and 5# of Radish per acre.  The main thing we observe in this plot is the larger radishes than we saw with the mixes of annual ryegrass, crimson clover and radishes.  Now, in this mix there are more radishes than in the previous two plots (see previous post).  So we have 2-3#/acre more radishes yet larger radishes.  Again, this is NOT scientific, but it sure appears that the radishes, which are luxury consumers of nitrogen, are much larger…thus I conclude, have been fed more  nitrogen from the peas.  It was quite surprising to me to see how much the peas have grown sine I last saw the plot in early November.  The cooler weather seemed to really allow them to grow at a faster pace.

In the second video on this you will see the plot that appears to have the most nitrogen produced.  This mixture is of 17#/acre of AU Robin Crimson Clover and 5#/acre of GroundHog Radish.  In this plot the radishes are noticeably larger in girth and above ground growth.  In fact as you look across the plot it is obvious that this plot is the most “robust” in its growth. In the spring of 2011 I anticipate that the AU Robin Crimson Clover will still be producing more nitrogen.  From previous cover crop field pits we have dug this fall we have found roots on the crimson clover at 24″ deep.  So we have deep rooted cover crops with both items in this mixture as well.

In both of these plots you have excellent nitrogen production and nutrient scavenging!  Personally I like that for a cover crop.  What do you like?

Cover Crop plots in December-What can we tell now?

The first day of December brought the first day of snow in northern Indiana.  After the inch or so of snow and some Arctic air the cover crops are shutting down.  Over the past three weeks we received around 5″ of rain so the cover crops were actually growing fairly well heading into December.  Now the question is, what can we tell in December as the cover crops are shutting down.  My answer is “plenty”!

Now that the radish tops are wilting and the peas and annual ryegrass are falling closer to the soil surface you can see the radish tubers more easily.  From the radish tubers I believe we can now see how much nitrogen is being produced from the crimson clover and Austrian winter peas.  Now, this is NOT scientific…but it is pretty obvious that the radishes were considerably larger where there was more crimson clover.  I’ll be posting videos so you can make the observation for yourself.

For your information, the Mixes we are looking at on this post have similar species (different varieties) at different rates/species in the mix.  The first video has more annual ryegrass than the mix in the second video.  The second mix has more crimson clover and also one more pound per acre of the radishes,  So the big difference is in the amount of clover in the mixture.

Now, I’m not saying one mix is better than the other.  It really depends on what your goals are.  In mix #1 there are more deeper roots because of the annual ryegrass.  In mix #2 there appears to be quite a but more Nitrogen being produced (therefore larger radishes-even though there are more radishes to feed).  Mix #2 has approximately 10# of Bruiser annual ryegrass, 7# of AU Robin Crimson Clover, and 3# of GroundHog Radish.  Mix #1 has approximately 15# of Bounty Annual Ryegrass, 3# of crimson clover (I don’t know if it is VNS or a variety)  and 2# of Tillage Radish per acre.  Both mixes have outstanding radishes, outstanding annual ryegrass and I know mix #2 has an outstanding crimson clover.  So it’s not like one good mix and one bad mix…both are good.

So, which mix do you want?  Do you want more nitrogen?   Or do you choose less nitrogen but 5# more annual ryegrass for additional deep roots?  Let me know what you are looking for!