Which does the most damage, tillage, herbicide, or fertilizer?

When growers discuss the damage to soil biology from herbicide applications, and possible alternatives, one of the first questions/justifications is: “Doesn’t tillage harm the soil more than herbicide applications?” Michael McNeill believes applied products often have a bigger negative contribution than tillage.

From the Regenerative Agriculture Podcast with Michael McNeill:

John: You’ve iterated several times that you have to stop doing what inflicted the damage in the first place. What I heard you saying was that it’s really the herbicides and fungicides and the insecticide applications that are causing this degradation of soil health. And I heard you mentioned that these herbicides and these various pesticides that people are applying are actually chelation agents.

Why do you believe that these products are the causal agent for the suppression of soil health? Couldn’t it also be the extensive tillage that we had for a number of decades and some of these other contributing factors?

Michael: Well, I have some farms that I feel are way over-tilled. They’re organic farmers. They really do till excessively, in my mind. But it doesn’t seem to be bothering the soil at all. It isn’t quite as good as I’d like to see it, but as long as they’re keeping their organic matter up, preventing erosion, using cover crops, and that sort of thing, the tillage in itself doesn’t seem to be doing as much damage as I originally thought it would.

Now, having said that, you have to be careful which tillage tools you use. A disc is not a very good tillage tool to be using—it causes compaction, it fractures the soil structure much worse than a tined implement that you could pull through—whether that be a v-ripper or a narrow-pointed field cultivator. These kinds of things do not seem to do the structural damage that I see with things like the disc, or even like a moldboard plow or a field cultivator with sweeps on it.

John: In essence, you’re saying that tillage doesn’t have the damaging effects on soil health that the herbicides do, from your perspective.

Michael: It’s not as bad as the herbicides, not as bad as anhydrous ammonia, and not as bad as the high-salt fertilizers. They tend to be more of an issue. And when you put them all together, it overwhelms the soil-life system.

John: I understand the impact of anhydrous ammonia and salt fertilizers—both of those are very oxidizing and can have the potential to produce a lot of damage to the soil’s microbial community. But I don’t understand how herbicides would have that same effect. You mentioned herbicides being chelating agents. From your perspective, how is it that herbicides and these various pesticides have such a damaging effect on soil health?

Michael: We have not paid a lot of attention to micronutrients in the soil. Micronutrients are extremely important to plant growth. And they are readily and easily chelated by the pesticides that we use. And once you tie them up, you start shutting down significant pathways. That’s where my physiology training and background came into play—when I started seeing a lot of these physiological processes being shut down.

An example people are probably familiar with is that if you chelate manganese and tie it up, you shut down the shikimate pathway. When you shut that down, diseases can move in very quickly, because that’s sort of the plant’s immune system, if you will. If you shut that down, you have to buy fungicides. You put on the fungicides to protect your plant from the disease that’s invaded, and then you start killing more of the fungal life in the soil. And it’s a vicious, vicious cycle that you’ve set up.