Gaining Ground: Digging Deep on the Impacts of Tillage

Gaining Ground 2First, a confession: I love plowing. Growing up, fall plowing was always one of my favourite chores, and I’ve still got the trophies I won in various county plowing matches as a teenager. Even now, few things give me as much satisfaction as an arrow-straight, neatly-turned set of furrows. It makes me a dinosaur, I know – I’m doing my best to reform my practices and maybe even appreciate the beauty of trash (oops, I mean “residue”). So let’s look at tillage from the perspective of soil health and soil biology.

Why Till?
All but the staunchest of no-till advocates will admit that there are benefits to tillage, even with respect to soil health. Tillage incorporates residues into the soil, bringing them in greater contact with soil organisms and reducing nutrient oxidation and/or surface leaching. It also adds oxygen to the soil and releases carbon dioxide, providing a boost to both soil microbes and plant photosynthesis (it’s easy to see this effect after row cultivation or even side-dressing – the nitrogen isn’t the only thing creating a crop response). Carefully-timed tillage can also aid in water management, either by breaking a crust and allowing water to soak in, or by creating a “dust mulch” at the soil surface by disrupting soil pore channels that increase evaporation rate.

Why Not Till?
On the other hand, tillage has been described as a “tsunami” in the microcosm of the soil. It is particularly destructive to the higher levels of the soil food chain and destroys the delicate fungal hyphae networks that contribute to both plant health and soil particle aggregation. No form of cultivation improves soil structure and aggregation. Excessive tillage, particularly in the absence of sufficient organic matter additions, will introduce too much oxygen, “burning up” soil organic matter and “burning out” nutrient-cycling soil microbes. The net result of this, coupled with a lack of surface residue, is soil that is prone to erosion and compaction. Over the long-term, reducing or eliminating tillage will allow a higher diversity of soil life to function and flourish, leading to better nutrient retention and cycling. (For background information on what lives in soil, see this post here.)

Guiding Principles
Our challenge as farmers is to find a method that maximizes the benefits and minimizes the drawbacks of each system. The first step is to admit that there will be no “one answer” that fits all crops, all farms, all regions, all years. Knowing and applying these principles will help balance short-term production goals against the long-term goals of building more resilient, self-sufficient soils.

  1. Stay out of the middle. The greatest diversity of soil microorganisms occurs in the aerobic zone. If you must till, keep it as shallow as possible to minimize disturbance to this middle layer. Or, if compaction is an issue at deeper levels, use a ripper at the correct depth to shatter that pan.
  2. Allow time and space for recovery. Maintaining the middle zone allows soil life to re-colonize disturbed soil above and below it. In the horizontal plane, strip-till methods allow for a similar process to occur – once the seedbed is established, soil life can move back in from the sides.
    Timing is another key concern: late fall is the worst time for tillage because soil life has no opportunity to recover before everything goes dormant over the winter (earthworms are actually most active at soil temperatures of 5 to 8 degrees Celsius).
  3. Keep a lid on it. Food and shelter is just as important for soil microbes as any other form of life. A green roof and living roots is the ideal, but a brown roof is still better than no roof at all. Terminating cover crops and sod can create challenges here, if herbicide use isn’t an option; again, the ideal is to till earlier rather than later, as shallow as practical, to establish another crop as soon as possible, and to leave some residue on top. Some farmers use equipment designed to “undercut” cover crops like clover a couple of inches below the surface while minimizing soil disturbance.
  4. Monitor and measure. Know the effects of your tillage and other soil management practices, both in the short and long-term. Research demonstrates that it’s not always safe to assume that no-till is better than conventional till. Other management practices can have a greater impact than choice of tillage on overall soil health and productivity. I beat myself up for the plowing, tilling, and cultivating I do to grow vegetables, but when I compared soil test results, the organic matter levels on these fields were actually increasing over the course of the crop rotation.
  5. Put biology to work on your side. Perhaps the most important thing to realize is that in a healthy, fully-functioning soil, all of the benefits of tillage can be realized with biology rather than steel. Earthworms and other soil organisms are great at incorporating residues, and tap-rooted cover crops can break up compaction. Soils high in organic matter and biological activity will not be as prone to crusting or erosion and will be well-aerated. In many ways, tillage replaces biology, at a cost to the farmer and the soil.

Smart tillage is using the minimum necessary to create an aerobic soil, eliminate compaction, control weeds and manage residues. If tillage requirements decline over time, soil health is headed in the right direction!

Gaining Ground is a multi-part series on cultural management practices for all management systems with a heavy emphasis on the importance of soil health and productivity. For the entire list of articles, click here.

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