The growers we work with who regenerate soil the most rapidly, and produce the most profitable crops, care for the cover crops as closely as their cash crops. Cover crops are planted with inoculants and nutritional support, and foliar fed. When you calculate the increased efficiency of a cover crop at 60% of it’s photosynthetic capacity as compared to 20%, and realize that it is sequestering three times more carbon in each 24 hour photoperiod, you quickly realize there is no other management practice which can build soil organic matter levels as inexpensively as harnessing the photosynthetic engine of a crop.
These crops can stimulate biology and build a large reserve of plant available nutrients that completely displaces the need for any soil applied fertilizers for following crops.
Here are some thoughts from my discussion with Gary Zimmer on this topic.
John: We’ve been talking about nitrogen management, and a few moments ago you were describing humic substances. One of the pieces that you and I spoke about in our prior conversation was the idea of delivering nutrients much more efficiently and much more effectively using carbon-based fertilizers. I think this ties in directly to our nitrogen management conversation, because what we’re really talking about is the need to have a balanced carbon-to-nitrogen ratio in the soil profile, and to hold that and to stabilize it and to keep it plant available. How does that concept of carbon-stabilizing nutrients transfer to other nutrients, in addition to nitrogen? And how do you utilize that?
Gary: I think this goes back to digestibility. In order to have the biology do its work and break it down, you need trace minerals. How do we make them available? Some of them, like molybdenum, are pretty small additions. How do we take that addition in very small amounts and make sure it’s active and plant available? By burning up carbon, those nutrients get lost. That’s the whole thing with carbon. Let’s say I just put some of this stuff out there and grew a plant and then managed the digestibility of that plant. I’m now going to be more time released, and I’m going to be distributed better. A farmer asked me the other day if he should put trace minerals on his cover crop. A cover crop is not a cover. It’s not covering anything―it’s actually a crop that you’re using to distribute minerals for the next crop, and you need to manage it accordingly. Managing the carbon ratio comes in line in terms of digestibility. If I’m too low on carbon or nitrogen, it’s going to take a long time to break down. I can set myself up for disease and insects, and I don’t get availability of my minerals. I’m a dairy nutritionist. That’s how I got introduced to some of these things forty years ago―to create better feed for cows. When we started, I spent nine years at the university balancing rations based on a set of numbers. If you have more digestible feed and the mineral levels in your feed are higher, that highly digestible feed might have 95 percent of its minerals available to the cow. The stuff you buy in bags might only be 40 percent available. When we started balancing rations for cows―and I think it’s the same thing with soils― once we started using highly mineralized, digestible feeds, we could actually cheat on numbers and cut down what we applied by at least 25 percent. We could back off those ration numbers with a lot of success once they started mixing minerals into highly digestible feeds. In the soil it would work the same way. That’s why it takes several years to really get this going. For us as organic farmers, during that two years in transition from conventional to organic, we remineralized and grew cover crops to build up our soil. Once it was organic it was far from perfect, but we started getting a higher nutrient exchange. It’s all based on first getting out there and building carbon-biological cycles with plants and biology.
John: Essentially, Gary, what you’re describing is that farmers should grow their cover crops as a ration for soil biology―similar to growing a ration for rumen biology. In saying that, do you believe that farmers should manage their cover crops as carefully and as well as they do their actual crops?
Gary: Yes, I think those cover crops are my reserve to hold and release the kind of minerals that I want to release. The other day a guy asked if he could just spray homogenized trace minerals onto his cover crop. I don’t know whether they get absorbed or where they go; I think that’s certainly not a bad idea. Then asked if he could use a cheaper source of those minerals, and I said that they still have to be able to get into the plant. I’m not sure how that would really work. But it starts with the process. The last thing I want them to do is spend money on something and have it just be another stone added to the big pile of stuff that we already have in our soil.
John: We have observed that our most successful growers―those who have regenerated soil health the most rapidly and who have achieved the greatest crop responses―manage their cover crops as carefully as they do their crops. They use foliar sprays and will put on fertilizers; they will manage those crops as well as they do the crops that they’re actually harvesting.
Gary: I’m 100 percent in agreement with that. I was just at some farms that had some really poor stands of alfalfa, and their cover crops were half a stand. They said that they weren’t getting much success. But they didn’t really have a very good cover crop or a very good alfalfa stand to work back into the ground to feed the soil―obviously they’re not going to get all the benefits. I think you’re absolutely right. I think that’s a huge ticket to using cover crops. As a dairy farm, we only leave our alfalfa in one or two years. We like to take that beautiful, lush stand of alfalfa grasses and let it get up to that highly digestible stage and work it back into the soil. And people say, “Oh my gosh―I could be feeding that to my cows!” But I say that I am feeding it―to my soil livestock. They need to be just as well fed as our cows.