Learning How to Rotovate a Green Manure Cover Crop

In mid-August we rotovated (shallow-tilled) our sorghum sudangrass and cowpea cover crop.  This post will describe the learning curve we encountered with our first time rotovating and how we got it to work.

Good mix of brown and green plant material

We planted this cover crop at the end of April, let it grow to about 5 feet tall, and mowed it in July.  Our bush hog made a lot of nice mulch.  After a week or so, the sorghum sudan and cowpeas came charging back mean and green and grew about 18 inches.  This is exactly what we wanted.  We wanted to rotovate green plant material “green manure” to feed and jumpstart soil life, and brown mulch material to breakdown and transform into organic matter.  These fields (our neighbor’s) were previously planted in no-till roundup-ready soybeans for at least a decade.  Organic matter is very low, below 2%.  Our goal is to stimulate all the soil critters to grow and multiply and bring life back to the fields.

our 7-foot rotovator

Rotovators are tillage tools, like a very wide garden tiller.  Our rotovator is 7 feet wide.  It has no wheels.  Instead, it skids along the ground like a sleigh, and the tractor’s 3-point hitch keeps it level.  We rotovated 25 acres of sorghum sudan and cowpeas (our neighbor’s fields) and two acres of our own grass fields.  In addition to the rotovator, our tractor was carrying a homemade spray tank on the front.  The spray tank is described here, and the spray mix (beneficial soil microbes and other goodies) is described here.

Why Rotovate?

We want to decrease the time it takes for the fields to get healthy.  Our own fields, which were previously under the same soybean farmer, have been in pasture grass for the past 3 years.  We’ve been mowing 2 or 3 times per year, fertilizing, and applying compost.  Unfortunately, we’ve seen very little improvement in the grass.   After studying biological farming techniques, we’re convinced the soil needs some disturbance to break up the sandy, crusty topsoil and to get a good dose of plant material and biology into the root zone.

Incorporating a green manure crop is essentially chopping plants and feeding them to the soil.  Five percent of a plant’s makeup comes from the soil (ash/minerals), and the remaining 95% comes “free” from photosynthesis of sunlight, water and air.  Incorporating the minerals (now in plant form) and all the free stuff like carbon, vitamins, and plant metabolites, provides a huge benefit to the soil in terms of improved soil structure and energized soil life.  We’re aiming for “chocolate cake” soil:  very dark, loose, and crumbly with high organic matter and a very healthy soil ecology.

Starting Out

Our goal was to rotovate as fast as possible (to decrease time in the tractor) and still be satisfied with the results.  In terms of results, we wanted to see most of the mulch incorporated into the top 4 inches of soil with a good mulch cover left on the surface for protection.  We also wanted to see a relatively smooth seedbed, but not so smooth that our sandy soil was pulverized.

We quickly discovered that getting our desired results would take a lot of trial and error!  On top of taking a large amount of time, rotovating includes many variables:  tractor speed, rpm, soil moisture, rotovator blade depth, vegetation content, row coverage (overlapping), and the position of the rotovator’s back gate.

Rotovating too slowly- powdery soil with little surface mulch

Lesson #1:  Don’t go too slowly.  On the first day, we started rotovating in our tractor’s 2nd lowest gear at about 1900 rpm.  (The rotovator manual said 1900 was the max).  This is moving VERY slowly, about 2 mph.  2nd gear cut the plants off at ground level but left them all on the soil surface.  The blades seemed to be bouncing a little instead of digging down.  Then we tried 1st gear at 1900 rpm.  Going slower allowed the blades to get into the soil, but the rotovator now chopped the soil way too much and turned it into powder.  All of the vegetation was incorporated with hardly any protective mulch on top.  It was getting dark, and we hadn’t even finished two acres.  We decided to sleep on it and try again tomorrow.  That night, it started raining heavily.  I had nightmares recalling the old 1930s TVA movie clips showing drastic soil erosion!  I didn’t feel good about the soil turning to powder.  It felt like a giant step back, and I was worried.

Pile made by rotovator catching mulch from previous row and dragging it.

The next morning, we walked out to look at the fields.  No erosion at all, everything was fine.  Except now in the morning light, we could see all the big piles of soil and mulch the rotovator created.  One side of the rotovator kept catching on the mulch in the previous row and dragging it until it balled up big enough to discharge out the side.  It was discouraging because we didn’t want to bring our tractor back over those nice and fluffy rows to smooth out the piles.  The tractor is heavy and would compact the soil and remove all the air that microbes need when they’re working.  Looked like we’d be pitch forking them by hand!  (We did.)

Lesson #2:  Don’t rotovate bone-dry soil.  We waited a few days for the rains to stop and the soil to dry out.  We knew 1st gear was bad, so we tried 2nd gear again at a little lower rpm, 1800, and we also set the blade depth deeper.  Voila!  It worked!  Most of the mulch was getting incorporated with some left on top.  But the major lesson here was soil moisture.  After the rain, the moisture level was now just right.  The soil’s aggregates stayed together in nice, small clumps.  It was too dry on the first day, and that’s why it got pulverized so easily.

Uneven seedbed from rotovating in 3rd gear with gate up

Lesson #3:  Leave the back gate down if you need a smooth seedbed.  We were still making the big piles though, and we couldn’t figure it out.  We decided to go faster, in 3rd gear, and lift the rotovator’s back gate up so all the mulch could leave without balling up.  This just helped make the piles a little smaller.  Also, keeping the back gate up left the soil surface very uneven.  That was another concern because we didn’t know how the drill (planter) would perform in a seedbed that bumpy.  We put the gate back down.

Lesson #4:  Don’t overlap rows.  It wasn’t too much longer when we discovered what was making the big piles.  I was bringing an iced tea out to my hubby in the tractor.  When he saw me to his far left, he turned his head and waved.  I saw the tractor and rotovator steer to the left far into the previously rotovated row, and a giant pile came out the side!  From then on, we concentrated hard on keeping the rotovator squarely on unrotovated ground.  This was hard to do continuously, but it worked!  We ended up leaving very narrow strips of the cover crop standing just so we’d avoid the piles.  This didn’t look very good, but we’re fine with it because the sorghum sudangrass and cowpeas will both die at frost.

Just right - moist soil, most of plant incorporated with plenty of protective mulch left on top

Lesson #5:  Do lots of test runs on the day you’re rotovating.  We ended up going back down to 2nd gear at 1800 rpm for most of the job.  The cover crop was very lush and thick in some places, and we needed a slower speed for most of it to get incorporated.  However, when we rotovated our 2 acres of pasture grass, we could go back up to 3rd gear.  The density of the vegetation makes a difference.

With all the variables involved, it’s key to test before you start to find the happy medium for that day.  Make sure your soil has some moisture (but not anywhere near wet) and start testing to see what speed and rpm gets most of the plant material below the surface and still leaves a protective mulch cover on top.   And if you start creating big piles, stop overlapping the rows!

Hurricane Irene Side Note:  Irene came two weeks later with 85 mph winds and 10 inches of rain.  The next morning, there was surprisingly little water standing and no sign of erosion.  The large quantity of mulch, both below and above the surface, protected the soil well.

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9 responses to this post.

  1. Posted by Cheyenne on September 4, 2011 at 9:24 am

    I’ve been using a rotovator on our farm since 1996, and it is the perfect tool for mulching in anything. I tend to go 4 to 5 miles an hour with the trailer boards up, partly because we have a lot of rocks and they can pass through the machine with less clunks. We then pick off the rocks and do a second pass at similar speed. It seems to work better than 1 slow pass. I agree, it takes trial and error to figure out what works best on your farm. Sometimes, I put them down and others I leave them up for the next pass. I think the most important thing is to not overwork the soil, as you mentioned about going too slow. I want just enough tillage to make a decent seedbed, and if I’m not seeding down, there is a lot of leeway.

    To limit the piles, make sure the machine is level and not tilting forward at all, and maybe try a shallower depth, but that may mean a second pass. I was rotovating yesterday on an old pasture sod with tons of dense grass and residue on top. As long as I stayed in the top few inches it was fine, but if I tried going deeper, it would gob up on the edge. It is only an issue with a lot of residue.

    It’s great how much rain can soak in and how protected the soil is with the litter on top. I’ve had no water run off my tilled hill, while it poured off my neighbors flat fields. I also find it holds the cows up better than a plowed field would when we graze off the annuals. (oats, turnips, rye, triticale, Japanese millet, sorghum sudan) I’ve grazed in some wet conditions with little pugging because of all the root mass and mulch mixed in.

    Sounds like you need some animals grazing on the fields you are mowing off? I just happened on your blog, looks great BTW. Bovines add so much to the soil improvement cycle, with their microbes, bacterias, etc. in their manure and saliva.

    We’ve been rotational grazing since 1994, and brought a mined out farm back to life, with more to do, so I know what you are dealing with. It is a challenge, but you will learn so much and be able to help others in the future. Think of the millions of acres that have to be converted and brought back to life as we bring life and health back to agriculture! 🙂

    Reply

    • Cheyenne, thanks so much for the rotovating tips and the encouragement! That’s so cool that you’ve brought your farm back to life. The piling depending on the amount of residue makes sense. We did have lots of residue. Sorghum sudan was probably not the best crop for us to start with! Very nice to hear about the rotovating decreasing pugging. I’ve been wondering about that. We do indeed need some grazing animals to really bring back our soil. We are unfortunately both stuck in full-time jobs with long commutes, but hopefully this will end next year.

      Reply

  2. Posted by Rich on September 4, 2011 at 1:57 pm

    Out of curiosity, why did you choose to use a rotovater instead of something like a disc?

    Reply

    • We didn’t think about this as much as we probably should have :), but i was influenced heavily by Gary Zimmer’s books on biological farming. He’s a big proponent of the rotovator for what it can do in one pass, and i found out that Louis Bromfield adopted the rotovator too. Another reason was familiarity. We know what a garden tiller does, and a rotovator seemed like a doable step up from that. We have no experience with discs. Another reason is the rotovator’s size. It takes up much less shed space than a disc.

      Reply

  3. Posted by Cheyenne on September 5, 2011 at 9:33 pm

    When you rotovate something with less “mass” it will flow smoothly and will be much easier, but then you won’t have the amazing amount of organic material either. There are a lot of farmers that would call you crazy for “wasting” such good feed. LOL!! They never think about the livestock we are feeding below the surface, and the long term benefits they will give us.

    A disk will take several passes to do what a rotovator can do, unless you have an offset disk. I’m not sure how a disc would handle sorghum sudan or a massive pasture sod like I just tilled in.

    Reply

    • Posted by Rich on September 6, 2011 at 10:33 pm

      Isn’t feeding livestock one of the purposes of growing these cover crops?

      Locally, there is a small dairy (40 head?) down the road that usually plants winter wheat in the fall and grazes it until about May. Then they run a chisel plow and field cultivator over the field and plant sorghum-sudangrass. When it has grown enough, they usually make enough silage to fill their silos and bale the rest of the field. After it regrows, they turn the cows out on it until early fall, when they run a disc then a chisel plow over it and plant winter wheat again.

      To my mind, they are feeding their livestock and their soil.

      Reply

      • Hi Rich, I agree that they’re feeding both the above and below ground livestock. And the manure is a huge plus. We plan to use many of these cover crops as annual forages for grazing when our perennial grasses hit seasonal slumps or we’re trying to finish a steer and need top quality forage for marbling.

        Have you seen SARE’s cover crop guide? I love that thing, and the chart on page 67 shows that all cover crops can be used for forage, except maybe buckwheat. http://www.sare.org/Learning-Center/Books/Managing-Cover-Crops-Profitably-3rd-Edition

    • @ Cheyenne – Microbes are livestock below ground…nice!

      Reply

  4. Posted by Rich on September 10, 2011 at 3:51 pm

    I have read most of the books offered online by SARE, (I try to read almost everything and anything I can find).

    There is a blog that talks about using cover crops in a no-till setting (I am currently no-tilling on our farm) at:

    http://plantcovercrops.com/

    Another subject that I am interested in and you might or might not be able to apply to your farm is pasture cropping or no-kill cropping. It is basically an Australian developed method of drilling cereals (winter wheat, oats, etc) into existing summer pastures for either grazing, grain, or a a combination.

    I have experimented with no-kill cropping by drilling wheat into a dormant native grass pasture for winter grazing, and drilling wheat into a bermuda pasture for a grain harvest. I’m far from working out all the details, but I only spent about $12 for seed and harvested about $30-40 of wheat per acre during a dry winter (plus the extra organic matter added to the pasture and the possibility of grazing during the winter).

    There is more information at:

    http://pasturecropping.com/

    I think the potential benefits from pasture cropping are high enough that it is usually worth drilling some wheat into existing pastures just to see what it will do.

    Reply

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