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Steve Groff inspects the cover crop mix he grew as a forage crop this summer. He recently planted winter cover crops into the summer mix, which will frost kill. The cover crops are part of Groff's plan to keep living roots in the soil at all times.

What are “greedy beans,” you ask?

That’s simply what some are calling double-cropped soybeans.

Lots of farmers plant soybeans after wheat to get a cash crop harvest ahead of the following year’s corn. The rationale behind this approach makes sense. Legumes like soybeans should do some work to improve the nitrogen in the soil and get it ready for the N-hungry corn crop next season.

Questioning the Practice

I used to plant double crop soybeans until I noticed that something wasn’t adding up. Even though I was supposed to be getting some additional nitrogen from my soybean crops, I didn’t end up being able to lower my N application (and costs) the following year.

I got curious and started studying my corn yields under different conditions, and I found it didn’t matter how much N I added after soybeans. Corn yields were consistently lower than when I used other practices.

Why Double-Crop Beans Didn’t Work

What I found instead was that the best boost for corn yields was — you guessed it — cover crops.

Double cropping soybeans doesn’t leave a good window for planting a winter cover crop after harvest in mid-November, so the fields don’t get the residual benefits of a cover crop ahead of the next cash crop planting, which is usually corn. Also, soybeans are hard on the soil. They don’t build carbon and their post-harvest residue doesn’t provide much soil erosion protection. You are also short-changing yourself on an opportunity to enhance biodiversity.

Cover-cropped fields easily outperformed my bare post-soybean fields, and for me the question was settled with research conducted on my farm.

Corn Yields After “Greedy Beans”

I did replicated plots with five nitrogen rates on corn following three treatments post-wheat harvest which had occurred the summer before.

The control plots were where no double crop soybeans or cover crops were planted. Weeds were sprayed once later in the summer. The two additional treatments were double crop soybeans and cover crops which included a mix of radish, sunn hemp and sorghum sudan grass.

In order to see the true effect of the cover crops and potential yield contribution of the double crop soybeans, zero nitrogen plots were used for each treatment. In the zero N plots, double crop soybeans did push the subsequent corn yield seven bushels higher compared to none, but where the cover crop mix was planted an additional 11-bushel increase over the greedy bean corn yield was measured. Even where we applied 200 pounds of N to the corn the following year — split between at-planting and sidedressing — the corn still yielded 9 bushels more compared to the double crop bean plots. But what may be more compelling is when all other N plots — 50, 100 and 150 pounds per acre — were included and averaged out, we realized a 14-bushel corn yield gain the following year.

What About Profit?

You might be saying yes, all that makes sense: double-cropped soybeans aren’t all they’re cracked up to be and increased subsequent corn profits may be in the ballpark of what you’d make with greedy beans. But don’t forget that pesticide costs may all but be eliminated with the use of a strategic cover crop mix. Overall fertilizer costs may be significantly reduced as well, particularly on the following corn crop. As you can see from the yield results above, and what I’ve clearly discovered over the years, cover crops make fertilizer more efficient.

Forage Opportunity?

Some may be suited to cash in on cover crops planted after wheat. The demand for forage in some regions provides this opportunity. Even though it could be argued that you are taking away some of the soil health benefits by removing biomass from these fields, the net loss is much less than what you’d incur with greedy beans. If manure can be applied, those nutrients are certainly replaced. In fact, some really like the added window of manure application opportunity that a field with cover crops can provide.

Doing a Double Take

Each year I hear of a few more farmers planting less greedy beans and instead using a prime opportunity to maximize the benefits of cover crops. Why not try planting a mixed species cover crop after wheat in a field and see how your corn responds the following season? With the current futures price of soybeans, this may be the year to try something different.

Steve Groff is a farmer and cover crop researcher in Holtwood, Pennsylvania. His website is SteveGroff.com

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