More Lessons Learned with Rotovating Sorghum Sudangrass (and a Bright Side)

Our rotovator fought the cover crop, and the cover crop won!  We grew sorghum sudan this summer on our neighbor’s fields as a green manure crop.  We rotovated it in early August to incorporate most of the crop into the topsoil.  We wanted the crop to feed the soil life and turn into organic matter.  Our goal is to move this dusty, sandy soil toward crumbly, black, “chocolate cake” soil that makes plants and animals thrive.

Rotovator Failed to Kill Sorghum Sudan

We also wanted the rotovator to kill the crop so we could plant the next cover crop of cereal rye and vetch for the winter.  We had very limited success here and still can’t tell what we did wrong with the rotovator!

Frosted sorghum sudangrass, 3 feet tall after failed rotovating

You can see the sorghum sudan in this picture taken in mid-November, about two weeks after a killing frost.  The sorghum sudan completely re-grew from the roots after rotovating and is finally starting to die from a cold snap.  Finally!

Rotovating is supposed to easily kill a crop, so we obviously did something wrong.  Perhaps the blades were not set deeply enough.  Perhaps we went too fast.  These scenarios are both perplexing though, because on the last field we set the blades to the deepest possible level, and the crop still grew back just as thick.  And the speed – we were going so slowly, I’m embarrassed to admit how long it took us to cover 20 acres.  Let’s just say days, and I won’t say how many!

I have heard that sorghum sudan easily grows back from the roots, such as after animals eat it down to the ground.  So maybe we just have to take extra steps when rotovating this crop and disturb the roots more?  We rotovated two acres of old grass pasture, and the grass died completely, no problems there.

Fluffy Soil Not Good for Planting

Another problem we need to figure out is extra fluffy soil.  The soil that the rotovator left behind was fluffed up, so much so that our boots would sink down about an inch when we stepped on it.  Turns out this does

our 7-foot rotovator

not bode well for the next crop.  We rented our county’s seed drill to plant the winter cover crop of rye and vetch about three weeks after rotovating, and it germinated very poorly.  I asked our Extension Agent for his opinion, and he said seed with poor soil contact has trouble germinating, and the 10 inches of rain from Tropical Storm Lee that we got right after planting likely made things worse.

So how do we make a good strong seedbed after rotovating?  We had the rotovator’s backboard down most of the way; maybe it should be down all the way.  Also, we can use time.  All the extra air eventually leaves the soil.  The soil needs at least 4 weeks to fully digest plowed down vegetation anyway (especially with no spraying of microbes), so we’ll just wait longer.  Our Extension Agent said our boots shouldn’t sink more than ¼ inch.  Any more than that, and the soil is probably too fluffy for drilling seed.

So far, I’m far from in love with rotovating!  It takes forever, and its performance feels like false advertising, far from the praise rotovators receive for their ability to kill plants, incorporate them, and make a nice seedbed all in one pass.  Surely it’s not too good to be true!  Hopefully it’s something we’re just missing.

Bright Side

Okay, enough of the whining!  There is a bright side.  Sorghum sudan is unrivaled among cover crops it its ability to produce biomass.  It gave us three good growths on zero added nitrogen fertilizer, and the root system below ground probably came close to mirroring the plant above ground.  We mowed twice and rotovated once, so that’s a good sloughing off of roots times three.  As the roots die and break down and form organic matter, the empty spaces will make great tunnels for earthworms.

Sorghum sudan’s other significant contribution is its amazing allelopathic (natural weed killer) effect!  During the 2010 summer season, these soybean fields were inundated with roundup resistant weeds like marestail and water hemp.  I can’t find nary a one now!  When we converted our own fields from GMO soybeans to grass pastures, we had to beat back marestail for 2 years by mowing.  Sorghum sudan is extremely helpful in this area!

Moving On…

We mowed the sorghum sudan for the last time in mid-November, as it was dying from frost.  The clippings made a good mulch for the soil.  The rye and vetch cover crop is growing well here and there, and cool-season weeds, Italian ryegrass volunteers (from previous winter cover crops) and the mulch do a good enough job of covering the soil in the other spots.  For this reason, we’re not going to replant the rye and vetch.  We plan to mow-kill the winter covers in the spring and then plant another summer cover crop like buckwheat.


5 responses to this post.

  1. Posted by Rich on November 17, 2011 at 12:14 am

    I have no experience with using a rotovator (except for using a rototiller in the garden), but I have a few suggestions that might or might not help.

    From your description, it sounds like you drilled your winter rye in early September, which sounds a little early to me (I could be wrong). Why not let your sorghum-sudangrass grow a little longer, rotovate it in mid September, and then drill your rye in early October?

    I grow winter wheat, and our drill is a no-till drill with a coulter setup. This fall, I drilled some wheat into a standing crop of grain sorghum (due to drought, it didn’t have a decent grain fill) about 2 weeks before our first freeze. The coulters chopped up the sorghum, flattening the stalks down on the ground, and incorporating some of the residue into the soil. The freeze killed any of the sorghum that was still growing and the wheat has germinated and is growing right now. Maybe you need to try a different type of drill with coulters, and use nature to freeze and kill your cover crops.

    The press wheels on your drill (if they have them) should be able to compensate for a fluffy soil (i.e. the press wheels should have enough down pressure to give your seed the right amount of seed-soil contact). But that much rain so soon after planting probably played a bigger role in your rye not coming up uniformly.

    I’ve planted smaller garden-sized plots of winter wheat or oats with a rototiller by tilling the area, broadcasting the seed (at a much heavier rate than drilling), then tilling again shallower. I don’t see why that wouldn’t work on a larger scale with your rotovater, and it might do a slightly better job of killing your sorghum-sudangrass.
    Instead of paying to rent a drill, you could just buy more seed with the money you are saving. There is a field just down the road from our farm that was planted this fall to winter wheat by broadcasting wheat (I would guess that about 3 bu./acre was used) into a seedbed, then using a field cultivator to incorporate the seed, so the same idea should work with a rotovator.

    I have also planted a cover crop of grain sorghum in the garden in late summer, then in early fall I broadcast wheat into the standing sorghum (similar to how a cover crop of ryegrass might be aerially broadcast into a corn crop). The wheat germinates, and as soon as a freeze comes, the sorghum dies and the wheat takes off. I’m not sure if that meets the criteria for biological farming, but it is an option.


    • Hi Rich, Thanks for your good advice! We did drill the rye and vetch in early September. We planted early to allow the vetch to really get going. Our extension agent recommended this, and I noticed the difference when i planted rye & vetch in our veggie garden. The vetch looks fantastic in beds where I planted early September. Rye is doing just as well in beds that I planted in early October, but the vetch is very short. Hopefully it will catch up in the spring time. I like your idea though, to do everything later and even let frost kill the cover crops. That is a good strategy, my only twinge is that winter cover crops seem to be especially good for soil (gives the soil critters places to hang out and go dormant during harsh winter weather), so I’m trying to figure out a way to use sorghum sudan and also get the winter cover going like gang busters in early Fall. I plan to try it on the small scale in my veggie garden next season.

      Thanks for the idea of a drill with coulters. The county has another drill, so we’ll check if that one has coulters. We’ve heard from lots of people that the press wheels should have taken care of the fluffy soil problem. I agree – there are so many variables – fluffiness, 10″ of rain, bad soil, sorghum sudan’s weed killing, etc, that the problem might not be the fluffy soil at all.

      For using the rotovator to incorporate seed – we would probably try that if the rotovator was wider. Ours is 7′ wide, and it seems like it takes FOREVER to cover ground. If we end up with extra fluffy soil again, we’ve thought about broadcasting the seed and then dragging a long heavy pipe or log over the soil to bury the seed a little and try to get some of the air out. Have you ever tried something like this?

      I did something similar to your sorghum and wheat in the veggie garden. I had buckwheat growing and let it stay and drop more seed and then lightly raked in rye and vetch. Worked great! the buckwheat is brown now from the frost, and the vetch is climbing up the buckwheat stems. It’s really pretty. That’s what I want to try in the veggie garden next year, but with sorghum sudan. i want to see if SS’s weed killing qualities snuff out rye and vetch. Our extension agent doesn’t think that SS has this effect on large seeds like rye and vetch, and I wanna find out for sure. Thanks again for commenting, Rich!


      • Posted by Rich on November 17, 2011 at 5:33 pm

        For what its worth, I am no-tilling on our farm, so some of my experience and suggestions might have a little bias or more relevance to a no-tilling mindset (although I am always reading about different techniques and am open to any new ideas). I want the ground surface to be covered with living or dead plant material and don’t really want to do any tillage. I also graze our cropland with cattle (sorghum stubble and wheat pasture in the winter, wheat stubble in the summer, etc.).

        I have only planted vetch in the garden, but there is always some growing in our pastures, etc., I have always noticed that the volunteer vetch seems to really start growing in the spring. So, I would assume that that is the growth pattern that the plant “wants” to follow. Planting late shouldn’t really be a problem and might actually be better, if it simply delays most of the growth until spring since volunteer vetch has that same growth pattern (I hope that makes sense).

        I’ve never tried to broadcast seed and incorporate it on a scale larger than a garden, except for one time when I broadcast some a native grass seed mixture on a pasture that had been cleaned up after a tornado. I then drug an old 16′ steel gate over the area with a pickup to cover the seed. You might be able to use a good steel gate covered with something like chainlink fencing and possibly a chain dragging behind the gate (i.e. use something like a 24′ logging chain hooked to the back corners of a 16′ gate) to smooth out your tilled area.

        Better yet, if you could find an old springtooth, you could cultivate your field after rotovating to dry out the SS roots and get a better kill, before you broadcast your next cover crop and springtooth it to incorporate the seed.

      • Tornadoes! Are you in OK by any chance? OK is my home state. We have volunteer vetch in our pastures too, and you’re right, the early planted vetch in our veggie garden is way bigger than the pasture vetch. I’ll see what happens in the spring and compare the two veggie beds. I wonder if giving it a head start will mean any more nitrogen added to the soil when I plow it down in the spring?

        No-till is the norm here. I heard it was promoted extra hard as a way to “save the Bay” from sediment erosion and ag runoff. Since so many farmers here took part in the tobacco buy-out, most acres are planted in no-till GM corn and soy, very few livestock except for Amish farms. We were originally going to keep everything no-till and operate like you describe, but it seemed that our soil needed some big intervention. That’s why i want to plant sorghum sudan again, because it produces so much plant material that we can put right back into the topsoil.

        I’ve got my hubby thinking about your steel gate and logging chain idea – thanks for the idea!

  2. Posted by Rich on November 18, 2011 at 11:38 pm

    That’s right, I live in OK.

    From my little bit of experience with it, I think no-till needs rotations to a variety of crops and cover crops combined with livestock grazing and hay production to work the best (at least in my area).


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