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Cut-and-come-again cover-crop experiments

Pearl millet

You may recall that I planted some experimental cover crops this year hoping they'd be cut-and-come-again mulch producers. The ones I was most excited about --- pearl millet and sorghum-sudangrass hybrids --- aren't really living up to their potential. These warm-season grasses remind me of corn in that they grow big stalks that require interim weeding and mulching, but the cover crop versions actually appear to produce less biomass than corn does. As a result, I feel like I would have been better off planting these beds with sweet corn or field corn then using the corn stalks if I wanted to harvest biomass from warm-season grasses. All told, I'm not very impressed by the warm-season grasses, even though sorghum-sudangrass hybrids are reputed to produce more biomass per acre than any other cover crop.

Scything soybeans

On the other hand, soybeans as a cover crop continue to intrigue me. The soybeans we planted on June 10 are just starting to bloom, so I chose one patch to scythe a few inches above the ground in hopes the plants will grow back and let me cut again in a few more weeks. While I was at it, I also scythed the buckwheat growing next door (planted two weeks later) and then I replanted the whole patch with new buckwheat seeds.

Before I go into the results, I should tell you that I'd been out cutting pasture weeds before embarking on this experiment, so my scythe was a little dull. As a result, the tool yanked up (rather than cut down) perhaps 10% of the soybeans. Gathering up the cut tops was easy, but I only got an armload out of this whole patch, which would probably be about enough to mulch 15 square feet in the garden. Lazily, I instead simply tossed the cut tops onto our compost pile.

Corn seedlings in dead soybeans

A perhaps better use of a soybean cover crop (although more expensive since the initial seed investment doesn't go as far) is to pull up entire soybean plants then use the legumes to feed the next crop. I yanked up the soybean plants in the bed pictured above less than a week ago, piling the cover crops in between rows of new sweet corn. The soybeans are so high in nitrogen that they're already disintegrating into the soil six days later, meaning they'll feed the corn plants by the time the roots reach the center of the bed. Whether or not the soybeans produce enough nitrogen to feed an entire bed of corn with no additional amendment remains to be seen. I'll keep an eye on leaf color and report back in a few more weeks.

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I've had luck with broadcasting southern peas during the rainy summer. They can take the heat and seem to fix a lot of nitrogen.

I've also been messing around with really complicated mixes of every kind of seed I can find - photo evidence here:

Some things really pop, some don't. The asjwain has been impressive, as has the sorghum. The castor beans barely managed to pop up a few plants here and there. Keep experimenting!

Comment by David The Good Wed Jul 22 23:11:57 2015

Hi Anna,

We have been growing soy for years now as edamame, to eat. I'm curious why you do not grow the soy until the pods are edible. Does it take too long? Are the plants not as effective at adding nitrogen once they fruit? I'm new to cover crops so please excuse me if my questions seem dumb. I was just surprised tha you did not mention harvesting before you cut down the plants- edamame is so delicious, and a great source of protein, excellent both lightly steamed with a little salt, or frozen and then mixed into winter soups. Thank you!


Comment by Grant Fri Jul 24 14:46:14 2015
Grant --- Great question! In general with legumes, you get the most nitrogen in the soil by killing the plants before they set seed. As soon as they start to develop fruits, the plants start socking away nitrogen there (as protein), so they pull it out of their leaves to do so. Of course, in some cases it's worthwhile to get a lower nitrogen harvest for the soil if you get a human-food harvest too! But I wanted to see what the soybeans would do at their peak.
Comment by anna Fri Jul 24 15:51:23 2015

Hi Anna I have been reading your blog for some time now and have learned so much. Soybeans as a cover crop fascinate me. Where do you find your seed? I'm curious about experimenting with them as a cover crop/ green manure. My "Ranchette' is in zone 9B. I live SW of Houston very near the Gulf of Mexico. I frequently see them as row crops grown commercially here. I am a fellow experimenter and would like to grow them. I enjoy eating them also. I find most legumes grow fantastic here- just poke em in the ground and let the South Texas heat and humidity do its thing. So I look forward to finding a good organic source. Are they heirloom? Thanks - Susie Q

Comment by Susie Sat Sep 26 21:28:36 2015

One very unique homestead, $1,500 per acre, the opportunity of a lifetime