This is Part 2 of a three-part series. In Part 1 we talked about the folks that provided very detailed diagrams of many plant roots to the depth needed to get the complete picture. In this part, we’ll talk about perennial plant roots, and in Part 3 will be about annual crop plants.
- Read more: Getting to the root of the matter
Thomas K. Pavlychenko from the University of Saskatchewan left a legacy of root mounts second to none in the world. You can see a silent movie of his work on the Internet on YouTube. (Go to YouTube and search “Pavlychenko Roots in the Ground”.)
John E. Weaver from the University of Nebraska made a life’s work of Prairie plant ecology including many root diagrams and publications. A quick Google search of J.E. Weaver, Nebraska reveals his complete works in PDF format from the University of Nebraska. The link is: http://digitalcommons.unl.edu/agronweaver/.
The Prairie sod
Let us begin by taking a peek underground at the root systems that were in place when our grandfathers arrived in the early 1900s to a raw new land. Figure 1 (top of page) shows the dense mat in a True Prairie (Black) soil. When we consider the biology and microbiology associated with that root system it is easy to see the huge transformation that took place when Grandpa came along with his breaking plough (see image below).
Weaver recognized three main rooting layers: zero to two feet, very dense; two to five feet, slightly less dense; and three to eight feet, only a few plants motored on to reach eight feet Such a plant community is well set to deal with the challenges of dry and wet periods.
It is not surprising that trouble arose when the dry years came. The wind blew, the grass roots were long gone and away it went in a cloud of dust. My Mother (as did many) oft repeated the Dirty 30s story of setting the table with plates upside down to keep the dust off the business side until dinner was ready.
It also drives home the common sense of folks that are pioneering work on multi-cropping and intensive short term grazing of broadly mixed stands. Kevin Elmy of Yorkton area, Colin Rosengren of Weyburn area, and the famous Gabe Brown at Minot, North Dakota come to mind. The current interest in “soil health” comes into sharp focus when we look at the root diagrams of Weaver.
Root growth and soil conditions
A plant ecology type gets all agog about what an individual or group of plant species can do. A soil scientist gets excited about a rich Black soil and what it can grow. But Mother Nature has to deal with the hand that is dealt. A plant capable of sending roots several metres into the ground may not always be able to do that. Sending roots deep looking for moisture does not work unless the moisture is there in the first place. Alfalfa is a good plant to illustrate.
In a situation of a rich lowland soil with a water table at 12 feet alfalfa roots reached a depth of 10 feet in only two years (Figure 3 below). With our recent wet years I have come to appreciate the profound influence that a water table within reach of plant roots has on what we grow. A shallow water table has also played a big role in determining the soil that formed from the parent material the glaciers and meltwaters left behind.
Weaver also examined two year old alfalfa at a dry site at Burlington, Colorado (Figure 4 below). At the two-foot depth the soil had a “hardpan” but closer examination showed that the hardpan was really just dry soil. In wet periods roots do penetrate the hardpan. The conclusion was that the hardpan itself was no barrier to plant roots when moist.
The granddaddy I have found for root depth is 17 feet for a herb (false boneset, Figure 5 below). Of interest with that deep-rooted herb is the reaction of roots to the soil/water conditions. The clay layers at eight and 12 feet allowed roots to branch out to make use of the extra water the soil provided.
A special example – curled dock
The final example is an “alien species from Europe.” It is not native here but the USDA map shows it from Florida to Alaska and all points between, including all of Canada. It likes wet spots and we see have all seen it on our farms. Amazing how a “foreigner” adapted so well to such diverse conditions. I had assumed it was native.
With a root system that reaches to three metres (Figure 6 below) and the numerous seeds that we have all seen, curled dock has settled in well. The example is from central Europe but our German was not good enough to pinpoint it exactly.
It is amazing that the plant has adapted to all of North America. It is considered a noxious weed in some U.S. states but not that I have found in Canada. Readers can enlighten me if I am wrong.
Stay tuned for Roots 3, which will deal with annual crop plants that we use to pay the bills.