Plant Cover Crops

Learning about the benefits of planting cover crops.

Radish

Cover Crop Turnips – A Good Choice Over Radishes?

Cover Crop Radishes or Turnips as a Cover Crop – or Both?

Cover crop radishes certainly receive a lot of press. I have researched them quite a bit over the past four years. On this blog alone I have over 20 posts about radishes. They are fun to take photos of, dig around in, research, and even play baseball with.

It is hard to pick up a publication that mentions cover crops and not read about radishes and their benefits.  Some industry and university cover crop research leaders like Steve Groff and Dr. Ray Wiel (University of Maryland) have researched radishes for over 10 years.You might say that cover crop radishes are the “Rock Star” of cover crop species these days.

What About Turnips?

The Oats are nearly 30" tall and the turnips are around 18" in this Oactober photo. The Cereal Rye was about 6" tall at this time. This mixture was planted in late August and the photo was taken Oct 22 - approximately 8 weeks after planting. My daughter Grace was the model..
The Oats are nearly 30″ tall and the turnips are around 18″ in this Oactober photo. The Cereal Rye was about 6″ tall at this time. This mixture was planted in late August and the photo was taken Oct 22 – approximately 8 weeks after planting. My daughter Grace was the model..

Why are turnips used as a cover crop so little compared to radishes? Are they the “ugly step-sister” of the Brassica family?

Let’s look at some of the benefits of turnips. Some newer varieties (Appin in particular) provide a bulb that is almost entirely in the soil and a deep root system (though a smaller bulb/tuber than the radish).

Benefits of Turnips

  • Turnips are very palatable for grazing cattle and sheep.
  • Most turnips survive the winter and hold onto nutrients into the spring (longer than radishes).
  • Turnips sequester nutrients in a similar fashion and amount as radishes (see data below).
  • Turnips are easy to kill in the spring.
  • Turnips do not have the odor problems that radishes have (therefore they can be planted more “safely” in areas closer to towns or neighbors).

“Problems” with Turnips

  • Not all turnips are created equal. The old purple top (or that type) turnip and even the tankard type turnips have very little of the bulb in the soil – thus less soil activity.
  • Most turnips survive the winter and then need to be killed in the spring. Yes this can also be a benefit.
  • The turnips “bolt” in the spring and want to produce seed. Kill them as early as possible.

    Turnips will overwinter in the spring. The turnips above flowered out in March 2012 in central Indiana. This is nearly 5 weeks before “normal”

Frequently Asked Questions

  1. If we mix turnips and radishes together, is that okay?  YES – for grazing or for just using as a cover crop.
  2. If we plant turnips instead of radishes is that okay?  Yes – just be aware of the differences and that the turnips will most likely survive the winter.
  3. What if we are just looking to graze and only care some about the cover crop?  Choose turnips.
These three brassica types were collected from a Loundonville, OH farm in the fall. Pasja Hybrid Brassica (L); GroundHog Cover Crop Radish (C); and Appin Turnip (R). Note the difference in tops versus tubers.

 

Nitrogen tested in Radishes/acre from Loudonville, OH dairy farm  averages 200 units of N (data collected November 2010)

Nitrogen tested in Appin Turnip/acre from Loudonville, OH dairy farm showed nearly 300 units of N (data collected November 2010)

The turnip tops had nearly 200 units of N/acre.  This was NOT scientific but it is instructive that turnips are an excellent scavenger of N.

Cover Crops Enhance Water Infiltration/Percolation

In late September of 2011 I was walking in our family corn field in central Indiana–in the pouring rain. Following the wettest spring in the eastern corn belt in 100 years we had a summertime drought that saw less than 2 inches in July and August combined. In that same time period we had 32 days above 90 degrees.

We just had 3 inches of rain yet my soil was dry at 1/2 inch in this area that had been tilled wet in the spring.

On this September day we were having rain…3 inches worth of glorious rain! I threw on my rain coat and Tingley boots, grabbed my shovel and went into the corn field where our cover crop plots had been planted in the fall of 2010 and killed in May 2011. As I walked through the field I noticed that where the soil had been tilled (see previous blog post) I was seeing dry soil underneath my boot track! Now catch the scene here…no rain for much of 60+ straight days…now a 3″ rain and virtually none of the moisture getting into the soil! Literally I had less than 1/2″ of the soil depth that was moist! Dry footprints followed me all the way to the end of the field. I was not happy.

When I reached the area where the cover crop test plot was (that area was not tilled this spring) I dug into the check area that was no-tilled yet did not have a cover crop. In that area I dug into the soil and I found moisture 2 1/2-3 inches deep. This area was now no-tilled for 23 straight years. That made me feel better.

Water was standing (or running off) of the soil that was tilled wet in the spring of 2011. There was very little infiltration from a 3 inch rain

 

In this photo we see infiltration at 2 1/2 - 3 inches deep. This soil has been no-tilled for 23 straight years.

 

Then I dug in the area that had been no-tilled for 23 straight years and had a cover crop the previous winter. I was very pleased when I dug in the areas where we previously had annual ryegrass and cereal rye and found moisture had filtered (penetrated) in 7 (seven) inches deep!

Water infiltrated 7 inches deep where we had corn no-tilled into cover crop rye.

 

 

 

This section of the field had a cereal rye cover crop in 2010-11 and was no-tilled. Note the lack of water standing on top of the soil! Where did the water go? Into the soil!

 

Watch these videos on what I found when digging for earthworms in this sections with cover crops and no-till and where there was tillage without a cover crop. I believe we have an additional answer to why I had so much better infiltration where I had the cover crops..earthworms and roots!

This "rogue" radish provided information that we had a compaction zone at about 3 inches deep in our no-till field; thus reducing water infiltration where we had no cover crop.

Yet, I wondered, why did the moisture stop at 2 1/2-3″ in the no-till plots? I found the answer from a rogue radish. We had a few radishes that came up in the field that had been planted in the fall of 2010 (the fall of 2010 was so dry that many of the radishes did not come up until very late…or not until spring, or in a few cases until mid-summer).  As I previously wrote, Radish does have some hard seed.  I dug around one of the radishes and found a constriction in the radish at 2 1/2-3″ deep! Even after 23 years of no-till I still had a compaction problem! I believe that is one reason why cover crops help producers to transition from conventional tillage to no-till…cover crops penetrate through compaction layers.

Big Radish fed by Crimson Clover

The video below shows the value of Crimson Clover in a cover crop setting.  Crimson clover has been tested and shown to produce as much as 140#/N after it has been planted after wheat.  The plots in this video were planted around July 29, 2010 by the Jasper and Newton County SWCD folks (Thanks Dan and Rose) at the Churchill Farms near Lake Village, IN.  The mix is called Crimson Cover-All sold in the N-Vest(R) line up by CISCO Seeds.  The planting rate was 21#/acre (approximately 16# Crimson Clover and 5# GroundHog Radish).  There was under 3″ of rain at this site from July 25 through Mid-October.  The soil is a sandy loam.  There was no additional fertilizer put on the plot.  The Radish in this video was weighed at Country Acres in Francesville, IN at 12# 14 oz.  It was one heavy radish…full of nutrients and water!  As that radish decomposes the water and nutrients will be released into the soil for the 2011 crop and for building organic matter.

You don’t always get what you want…but often get what you pay for!

This photo is from the Thumb of Michigan where we had great success with the Radishes (these were GroundHog Radishes). The seeding rate was 10#/ac and planted w/o a companion crop.

Over the past number of weeks I’ve noticed quite a difference in radishes growing in farmers fields.  Some are outstanding and consistent; deep and fairly large tubers (tuber girth seems to be related to fertility and age of stand).  In the thumb of Michigan I saw over 300 acres of fields planted at 10#/acre that were just what the farmer wanted.  We found tubers 8-12” deep and we could not really find the real bottom of the roots as we broke them off in the soil.

These VNS Radishes from North Dakota are fully headed out and now a weed for producers. Unfortunately, no one in the Midwest knew there would be a problem...but boy there sure was.

While some varieties have good tubers in other instances I have found real problems.  In a field in NE Indiana a SWCD director brought some radishes from a farmer’s field that did not look good.  The farmers planted around 100 acres of a VNS radish from North Dakota (labeled as “Daikon”) and he was not happy.  I don’t blame him…look at the photo below.

What makes this story even more interesting is that the VNS radish (VNS = Variety Not Stated) from North Dakota cost the farmer 30-40 cents less per pound than the GroundHog.  Unfortunately, he’s unhappy because his radishes are not performing.  I’ll say it again…”VNS could equal Very Nasty Seed”.  The farmer saved $3-4/acre and is frustrated.  Two things…and this is for dealers and producers…#1 –Choose to buy from a trustworthy source #2) IF there is a big price savings…beware there is a reason for that spread!  Saving 15-20% on seed is HUGE!  If there is that much saving ask questions and get good answers!