When I first heard of keyline plowing, and that it could build 8 or more inches of topsoil in a year, my “Believe-It-Or-Not-O-Meter” went off. Decades of studying soil, its chemical properties, the complicated ins and outs of how soil changes and supports plant growth, combined to tell me “This just isn’t possible.”
To find out if it was true, I had to find out: What is keyline plowing?
Keyline plowing is a form of subsoiling. Subsoilers are implements used to loosen and break up soils to double the 6 to 8 inch depths that a traditional disk harrow reaches. The tool used for keyline plowing is the Yeoman’s plow, a subsoiler with very thin shanks. Created in the 1950s by P.A. Yeoman, an Australian mining engineer and farmer, it was designed to lift and aerate the soil while limiting soil disturbance to minimize oxidation of organic matter.
Yeoman used his plow as part of a landscape design with an emphasis on addressing conservation issues facing Australian farmland where erosion and drought are major challenges. His idea was to capture water and move it across the landscape using “Keylines.” The keyline is like a contour line, in that it follows the topography of the land. It is based off the keypoint, described by practitioners as “the highest point on the landscape where one can cost effectively hold water.” That’s where the slope changes from convex, where it sheds water, to concave, where it collects water. Following the line of that point around the landscape produces a kind of topographical etching of the land. The keyline plowing pattern, following the keyline across the landscape, creates a drainage or water flow system to move water from wet areas to dry areas.
Where’s the Data?
Proponents of the Yeoman’s plow and keyline design cite a number of benefits. They say it reduces compaction, and can build up to a foot of topsoil per year. It is also touted as a method for increasing carbon sequestration. It seemed strange to me that simply ripping thin lines through a pasture could do all that. As a soil scientist, I look for data and so I began the search. I found nothing online, in journals, or from farmers who had tried it.
I attended a two-day course on keyline plowing with Darren Doherty, an expert on Keyline plowing from Down Under. I asked him for some data. He said that in one case, soil was tested before and after keyline plowing, and its CEC (capability to hold nutrients) went from 6 cmolc/kg to 12 cmolc/kg. But they also limed the soil while they keylined it. We all know that when soil pH goes up, the CEC goes up too. So the change was likely a result of the lime and his data were meaningless.
Here’s where I start turning into one of the two grumpy Muppets in the box seat. The buzzing from my Believe-It-Or-Not-O-Meter is going off like a smoke detector. Deep breaths, and we’ll get to the bottom of this.
I decided to study the practice myself and got together with a team from University of Vermont, including fellow soil scientist Josef Gorres and graduate student Bridgett Hilshey. In Vermont, four dairy farmers agreed to let us keyline plow their pastures. We partnered with Mark Krawcyk of Keyline Vermont. Mark is a wonderful guy, with a soft, clear way of explaining things. He worked with each of the farmers, showing them how he found the keyline in their pastures. He also keyline plowed each of the target pastures four times over two summers, following the recommended protocol for keyline plowing.
Even with Mark’s conservative pricing structure, it cost approximately $160/acre to plow the recommended four times. Add to that the cost of running the tractor pulling the plow, and the total cost for the treatment was $280/acre.
To measure the effects of keyline plowing, we collected soil and forage samples from the keyline plowed pastures and from similar adjacent pastures. For good measure, we also tested penetrometer resistance and rated the pastures conditions. We sampled before, during, and after the two years of plowing.
With thousands of soil samples, and hundreds of readings and scores, we found nothing; no increased organic matter, no changes in penetrometer resistance, no change whatsoever, unless you measure in worms. We did find more worms in our treated pastures.
There are folks out there, who are very nice people, who believe in the use of the keyline plow, who will be alarmed at these results. So next week, we’ll describe more about this trial and its results. We’ll even tell you more about worms and why more of them may not be as positive a result as you might think. Down the road we’ll also share some results from a study on the use of keyline plowing to enhance carbon sequestration. In the meantime, if you have experience with keyline plowing, and you have any data, please share it with us!