IS TILLAGE (PLOWING) BAD FOR THE SOIL?
Farmers and gardeners have been taught to tillage the ground, but tillage destroys soil structure and mycorrhizal fungi, a vital element in the soil ecosystem.
A conversation with geologist and soil scientist Dr. David R. Montgomery of the University of Washington. For the entire interview, please click on the link.
HART HAGAN: Is plowing bad? We have been taught to think well of the plow. The farmer plows. The farm yields food for us. So we have positive associations and feelings about plowing. But is plowing bad?
DAVID MONTGOMERY: That's a great question. It's a little bit like the answer I gave you on fertilizers where it kind of depends. But in general, yes, tillage is bad for soil health.
And how is that? Well, if you have things like mycorrhizal fungi in the soil, fungi that are beneficial to crops because they serve as root extensions for plants, they will go out and actually get things like phosphorus or zinc out of the soil, bring it back and give it to the plant in exchange for root drippings, root exudates, which are things like sugars or fats and proteins. Sounds a lot like food.
Plants will trade food for minerals that they need to build enzymes to help their bodily functions, and fungi are a big connection.
What happens when you run a plow through a field that has a fairly dense fungal network, you chop up those fungal networks and those root extensions for the plants. This disrupts those symbiotic relationships between soil life and crops.
But there are some advantages to plowing. It’s great weed control. That's one of the really big reasons that farmers will use it. It's great if the field that's full of either last year's crop or a weed, and you want a blank slate to plant in. Plow it up, and you've got fresh ground to work with.
The problem happens if it rains right after you’ve plowed. You've probably seen examples of that, where you get the brown runoff coming off fields.
The ground is no longer clothed in plants. Nature tends to clothe herself in plants. It greatly reduces erosion, and it also helps produce organic matter, which makes the soil more fertile, which means you can grow more plants. There's a positive feedback there.
So, tillage or plowing is one of those things where if it's done infrequently--because it's needed on a particular year or particular application--it might be okay. You might have a perennial weed that's gotten established and you need to wipe it out in a field. Plowing once isn't going to do that much damage but it's the regular application of routine tillage that does a real number on soil organic matter.
But, again, if you have, say, a small organic farm, and you have a neighbor that has a dairy, and you're using a whole lot of livestock manure from that dairy to replenish the organic matter on your small farm, you can probably get away with plowing regularly and not damage the soil organic matter because you're adding it back in.
That's really hard to do at large scale and especially if they don't have a convenient source of organic matter to draw upon. That's where frequent routine tillage can really do a number on soil health by both changing the composition of the community of life in the soil, and accelerating the decay of soil organic matter, which can leave farmers even more dependent on chemical fertilizers, because they have burned through their supply of soil organic matter.
Tillage is one of those things that it's not to be avoided at all costs, where at all times it’s bad, but it is the kind of thing that we probably don't want to rely on all that frequently.
In that respect it's kind of like alcohol.
HART HAGAN: Right. In moderation.
DAVID MONTGOMERY: Moderation is probably fine. A little bit every now and then it helps people socialize. But a whole lot all the time is completely dysfunctional.
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To hear the entire conversation with Dr. David Montgomery, please click on the link.