Cover-crop, cash-crop rotations: saving the environment and your checkbook

I’ve mentioned before that on my small scale, and given my commute to farm, all the time and machinery and fuel and labor adds a considerable cost per pound to my grain. I’d really like to be able to make it more affordable so more people could enjoy it and I’d get some more economy of scale. So I’ve been looking into the thirty years of research at Rodale Institute on organic cropping systems…specifically no-till. That is a system where you plant your cash crop into an existing mulch or living cover crop. No-till production of corn and soybeans has been well established in that time, but it relied on herbicides to kill the cover crop and any weeds. Rodale has been working on the organic side of that using a roller to kill the cover crop, but their research is oriented to the wetter climate of the Midwest and East. In California it’s not clear how well their system works because there have been some anecdotal failures.

Recently, a video was placed on the ATTRA (Appropriate Technology Transfer to Rural Areas) website showing research done in North Dakota aiming at continuous organic no-till that has me excited. You can watch it if you want, but be warned that it’s an hour long:

A local Soil Conservation District has done extensive work with local ranchers on improving soil health with cover crops there, based on the idea that it was all native prairie at one time which had huge stores of organic matter and perennial plants that sustained it for thousands of years and fed the seemingly limitless herds of buffalo. the farmA prinicipal part of that health would seem to be the microbiological life of the soil, as I mentioned in my previous post on tillage. The soils there are sandy loams without high fertility and they only get about 16 inches of water a year. Plowing up the soil loses a lot of the soil moisture and makes it hard for fungus, bacteria, and nematodes to survive. Since they help extract plant nutrients from the mineral soil it’s vital to support them.

Their research has been based on always having cover on the soil, avoiding tillage (plowing, disking, or otherwise turning over the soil), and using grazing animals to process the cover crops so planting of cash crops can be done. They use as many as fourteen species of plants in the cover crop mix, attempting to replicate the diversity of native prairie. The grazing down of the cover crop avoids driving heavy tractors over the soil and ads food for the microbiological life in the form of manure, hair, and saliva [1]. They did side-by-side trials at their Menokan Farm test site with compost and compost tea on one side and nothing but the cover on the other. The corn in both plots outyielded the county average and, even without compost or tea, had yields within a few bushels of the composted side. The idea is that from here on they will plant a cover crop into the corn stubble after grazing, graze that down, plant a cash crop into the cover crop stubble, and so on. No messing with the soil. Now that’s exciting.

the tractor and the disked cover cropThe Land Institute in Salina, Kansas has been working towards restoring the prairie while producing grain for many years. On their website you can see photos of soil cross sections of native prairie soil and soils that have been tilled since settlement. The native soils are about three feet deeper! The Land Institute has been trying to breed perennial wheat varieties that could be harvested and never disturb the soil, but success there is still decades away. What excites me about the North Dakota trials is that it’s something that can be done now to rebuild soil and, by the way, sequester carbon. Living plants all hold carbon that is released in the atmosphere when they are killed and decay. Soil organic matter holds twice as much carbon as plants and while soil organic matter comprised six to ten percent of untilled soil, today’s typical fields only hold one to three percent. Rodale Institute has done thirty years of research on the subject and concludes that with soil organic matter returned to the levels they achieved in their test fields, the 434 million acres of farmland in the U.S. would sequester carbon dioxide to the equivalent of taking one car off the road for every two acres. That’s only their research but it holds great promise.

Admittedly, North Dakota has a different climate and soil than California Central Valley and foothills. For one thing, we have soils very deficient in calcium, as I explained in the last post. But they are worse off for organic matter so the comparisons are not entirely inappropriate. One concern for the long-term future that I have when looking at my soils and most agricultural land is that our supplies of mined gypsum and lime are finite just as petroleum is. I need to add a lot of both of those two but somehow I have to avoid doing it forever. I think that’s where the microbiology will come in.

the combine at work in the fieldI am planning to do some of my own trials to see if I can use continuous cover crop/cash crop rotations. There is a cattle farmer who is renting land where I’m farming and he has divided my thirty acres into three plots. I’m hoping to put in a multi-species cover crop on the grain stubble in the fall of this year and have him put his cattle on it in late winter, taking soil tests before and after the grazing to see what happens. I will be plowing down my legume cover crop on the plot where I’ll plant grain this coming fall so that I can get some serious increase in organic matter. The soil tests on the grazed plot will guide what I do in coming years. If I can get good increase in organic matter and balance the minerals with surface applications of lime and gypsum, I hope that one day I can put away the disc and just plant into stubble. That would not only save lots of carbon dioxide emissions but would save me a lot of money in fuel, tractor repairs, commuting, and sitting on the tractor. My grain would become much more affordable as a result. That’s my project for the next few years. I’ll keep you posted on the results.

[1] The tests aren’t entirely organic because some of the fields started out with heavy weed pressure so they wanted to give the cover crop a running start with herbicides to suppress the weeds. After the one application of herbicide, though, they just grew a cover, grazed it down, and planted corn right into the stubble.

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