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!
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
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.
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!
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.