Tillage with a Purpose

March 20, 2023

Occasionally, there is hot debate about tillage versus no-till. In my opinion, both of them have their place. I certainly believe that no-till is beneficial to the soil and is the goal to strive for but I also recognize some of the limitations that is keeping farmers from doing that, especially organic farmers.

I have personally tried no-till vegetables in an effort to build soil health and limit disturbance to mycorrhizal fungi and other soil biology. Unfortunately, the soil I tried it on was 34% magnesium, which is very high, so I did not have the best experience.

My conclusion from the experiment is that soils need to be prepared for no-till. We should be using cover crops. We should try to balance soil chemistry, especially calcium to magnesium ratios. And we can use tillage to level the field as desired, to subsoil the hardpans, to terminate stubborn weeds, and to loosen the soil to get the process started.

However, when we use tillage, we need to be aware of the potential downsides. As a consultant, I was taught that tillage has the potential to destroy soil structure, but when it really hit me was when I was listening to a podcast where John Kempf was interviewing a farmer who was a long-term no-till advocate. The farmer got his soil in awesome condition using no-till; the soil was loose, lots of pore space, and good aggregation. Then he hosted a field day, and to demonstrate the soil structure, he dug a soil pit.

Now here is what struck me: After the field day was over, they filled the hole back up with the soil. Only, the problem was that it didn’t actually fill the hole. In other words, imagine a giant soil sponge that was then compressed to such a degree that it didn’t fill the hole from which it was originally taken.

To me, that is a remarkable story and example of how soil disturbance can cause soil structure to collapse. Normally after you have dug a hole and are ready to fill it back up, the soil will not all fit back into the hole – probably because we really had compacted soils to begin with. But in the soil pit example, the soil actually took up less space because the soil had not been compacted to begin with.

So if we till, we need to recognize that there are negative side-effects of using tillage that we need to understand, and to avoid if possible. In short, that excessive tillage destroys soil structure. After tillage, the first rain that comes along will usually create a crust, which then alters soil breathability, which will make weeds grow (because they generally thrive in low gas-exchange environments) and crops will not grow as fast because they need the carbon dioxide that is now being trapped because of the crust, not to mention that the right microbes won’t thrive either. And very importantly, excessive tillage will disturb mycorrhizal fungi, which then leads to less nutrient uptake because your plants no longer have extensions to their plant roots. And, plowing or disking specifically can create a hard pan from the sideway movement of steel.

The number of challenges that can potentially come from excessive tillage are so large that they can hardly be discussed here in detail. But what I wanted to point out is this: if you till, use gentle tillage. Avoid beating the soil to death or pulverizing it to a fine powder. Avoid the rototiller. Use a subsoiler if needed. Avoid tilling all the land if possible. If you need to plow, do it as gently as possible, and then go over it with a roller basket harrow the minimum possible while still getting a firm bed. And of course, avoid going into your fields when it is too wet.  And then get another living crop in as soon as possible.