Plant Cover Crops

Learning about the benefits of planting cover crops.

cover crop scavengers

Fertilizing Cover Crops & Planting Legumes After Soybeans

If you spend any time at all in cover crop meetings, you may have heard that it’s a good idea to add 20-50# of Nitrogen per acre to your cover crop – if you don’t have a legume in the mix or you don’t have manure available. You also probably heard (or participated in) the grumbling that predictably starts from the crowd. Who wants to fertilize a crop that they will not harvest?

While it’s true that producers will not “harvest” the cover crops, they will have healthier cover crops which should lead to healthier soils and healthier profits.

Manure as the No-Brainer

Obviously if manure is available it is a smart move to put manure where you will have or already have cover crops.  We know from research that cover crops can hold as much as 90% of the nutrients from manure applications.

We have also know that where manure is applied without a cover crop being present (even if worked in) we can lose a significant amount of nutrients into ground water or as surface run-off.

What About Adding Commercial Fertilizer?

The Radishes on the left had manure applied and those on the right did not have any additional nitrogen applied.
The Radishes on the left had manure applied and those on the right did not have any additional nitrogen applied.

But, what if there is no manure to apply and for some reason you do not want to include a legume in your system?

Is it worth applying 50# of nitrogen to produce a cover crop?

Let’s look at what we think we know:

  • Pages 22-24 of Managing Cover Crops Profitably provide formulas to figure out the value of using cover crops as a green manure in a cover crop system –  whether with legumes, manure, or fertilized.

Look especially at the section on “Potential losses” to see that there can be nitrogen losses even in this scenario.

  • Cover crop experts say to count on 50% of the N captured or N produced by a cover crop to be available to the next cash crop.
  • It appears that adding a grass with legumes or brassicas will help “slow down” the release of the N in the spring making it more slowly released to the next crop.

 

Here is a photo of the Ingham County Michigan Cover Crop Plot. Where there was a legume in the mixture there was considerably more growth and earthworm activity
Here is a photo of the Ingham County Michigan Cover Crop Plot. Where there was a legume in the mixture there was considerably more growth and earthworm activity

What can we expect if we plant a cover crop and we don’t add more nitrogen?

How will that cover crop do?

I will utilize work that Dan Hudson did when he was an Extension educator in Ingham County Michigan in cover crop plots he planted back three or four years ago.

  • Radish tubers are considerably smaller and the roots appear to not be as deep  (I have not dug a root pit in this scenario).
  • Grasses have a more shallow root system in forage settings when fertility is lacking.
  • The cover crops were pale green.
  • The “hungry” grass cover crops had less earthworm activity than in the grass + legume mix plots.
  • “Hungry” radishes and turnips had much less tuber and top growth, thus sequestering less nutrients (one of their main functions).
  • Winterhardiness on cover crops is potentially not as good when the cover crop is undernourished.

What can we expect after soybeans?

Do we need a legume in the cover crop mix following the beans or is having a grass and/or brassica to sequester the N from the soybeans good enough?

Let’s investigate the difference between adding a legume to a cover crop mix following soybeans compared to planting scavengers only.  The charts are from our family farm trials.  The charts show the chlorophyll readings of the corn in the year following the soybeans (and then following a cover crop).

It is important to look at the “Y” axis as each chart is slightly different in how it shows the top reading.

When Austrian Winter Peas were added to a scavenger (Radishes) the chlorophyll readings were very favorable compared to the no cover crop check plot and plots with just scavengers.
When Austrian Winter Peas were added to a scavenger (Radishes) the chlorophyll readings were very favorable compared to the no cover crop check plot and plots with just scavengers.
Just like the peas gave us an advantage over the no cover crop check the crimson clover showed very favorably.
Just like the peas gave us an advantage over the no cover crop check  and scavengers, the crimson clover also showed very favorably.

 

While the Oats and Radish showed exceptionally favorable in the early part of the season the plot are "ran out of gas" as the corn was pollinating.
While the Oats and Radish showed exceptionally favorable in the early part of the season the plot “ran out of gas” as the season progressed.
Straight Winter Cereal Rye was impressive early season but also did not fare as well against the check as the mixes with legumes
Straight Winter Cereal Rye was impressive early season but also did not fare as well against the check as the mixes with legumes.

As we looked at the yield of the corn in these plots we saw a considerable difference – suggesting that even after soybeans we might want to add a legume to improve the corn yield the following year.

Yields from the different cover crop plots shown above were:

Check Plot                                    105.24 bu/ac

Winter Cereal Rye                      126.86 bu/ac

Oats and Radish                          138.79 bu/ac

Crimson Clover + Radish           153.99 bu/ac

AW Peas + Radish                        164.82 bu/ac

Conclusion

All indicators seem to point that adding manure, a legume, or additional N might very well pay off when planting a cover crop, even after soybeans.  However, adding a nitrogen source is not necessarily vital to having a successful cover crop system.  I would suggest that you try different scenarios on your own farm and in your own system and see what works best for you.

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.”