In addition to exposing soil to wind and water erosion, tillage can alter the physical structure, distribution of organic matter and biological activity of soil. At the depth where the plow impacts the soil, a layer of soil compaction can develop (a plow pan), limiting water infiltration and plant rooting depth. Under tillage, crop residues, roots and root hairs and their associated fungal hyphae are disturbed and more decomposed in the plow layer. By contrast, when roots, fine roots, and fungal hyphae are not disturbed and decomposed as rapidly, there are more channels that water, air, earthworms, and roots can move through, and soil aggregation is enhanced. Below is a schematic comparing the root zone profile of a conventionally tilled soil to a no-till soil.
Figure 7.2.1.: Steps Toward a Successful Transition to No-Till. Credit: S. W. Duiker and J.C. Myers. 2005 Penn State University.
Watch the three videos below, from USDA NRCS about soil tillage and soil health.
Video: The Science of Soil Health: What Happens When You Till? USDA NRCS (3:05)
- Click for a transcript of the what happens when you till video.
Interviewer: When we use tillage, the soil ecosystem is disturbed on a massive scale. Purdue's Dr. Eileen Kladivko contrasted natural ecosystems with tilled systems, and what we stand to lose when soils are tilled. Eileen: If you think about natural ecosystems, they don't have a tillage implement running through them once a year or a couple of times a year, but nutrients get recycled and trees grow or grasses grow and what's recycling the nutrients are the organisms. And so, part of what we're saying with a with a no-till system, is that if you don't take an implement through there, and you allow the system to kind of come back, that there will be organisms that will do that job for you. They do it differently, obviously than a piece of metal would do it, but they can be very effective. And besides loosening the soil or making burrows, they do some of these other things, like convert nutrients, ok, recycle nutrients, have pathways where roots can grow and then those pathways stay there. You know, if you think about a tillage implement, any root channel from last year in the topsoil, is going to be totally broken up by a tillage implement the next year. If you have a nightcrawler channel, or even if you have a red worm channel, that's part of the red worm channel, it's there and then the roots can follow that and so you can have channel built upon channel, built upon channel. And the nightcrawler channel, you know, maybe a root, maybe a corn root, maybe a cover crop root, will go down that, and the next year another nightcrawler, and so on. So it builds upon itself. Interviewer: Will you explain to us why organic matter decomposes faster because of tillage? Eileen: A tillage operation does a couple things, number one is it opens up aggregates that were otherwise protected. So you're opening up more surfaces for the bacteria to decompose the organic material faster. That's probably the main reason. Sometimes people say well you're putting oxygen in the soil. It's not really so much that, as by breaking up aggregates, you expose the organic matter in the soil to decomposition. Whereas when it's in an aggregated state in the soil, some of that's protected and the bacteria that decompose that organic matter can't get to it. Interviewer: So the tillage actually favors then, say bacteria, that would live in that environment. And that may be what causes the flush of carbon dioxide and nitrates into the soil as well. Eileen: Oh yes, yes, the flush of carbon dioxide is very much related to the tillage, right.
2. Video: The Science of Soil Health: Nightcrawlers and Soil Water Flow. USDA NRCS (3:05)
- Click for a transcript of the nightcrawlers and soil water flow video.
Interviewer: When we get to those dry summer months, good soil hydrologic function is critical. We visited with Purdue University's Dr. Eilieen Kladviko to talk about the remarkable effect that nightcrawlers have on aiding water flow into and through soils. Interviewer: Well you’re a soil physicist Eileen, so we better talk about. Eileen: We better talk about water flow. Interviewer: Let’s talk about that water flow, because obviously water is a free resource to the farmer. Eileen: Right, in general our soils are excessively wet in the spring and that's more of our issue and that's why we use tile drainage (yes) and things like that. But what I'm getting at really is that the nightcrawlers, in particular, can be very important for getting infiltration of water into the soil during the growing season. So when we get those quick thunderstorms in the middle of the summer, we usually want all that water to go in, because that's not when we have excess water. So we want the water to go into the soil, but, but especially with soils that are high silt, sometimes you can get crusting (yes). You have less crusting of course, if you're in no-till (yes). But if you have a lot of nightcrawlers, those deep channels that the night crawlers make can really help get water into the soil profile, where you have a chance for your crop to use it, as opposed to having it run off. You know an extra inch or two of water in a lot of our summers makes a big difference (okay) in yield (yes, yes). And I happen to have a few demonstrations of some night crawlers, if you'd like to see, nightcrawler channels, if you'd like to see. Interviewer: I would love to see. Eileen: So this is, my technician a number of years ago, went out and poured the liquid rubber, latex basically, that you use in in biology classes, on an area where there were some nightcrawler middens (yes). And then he came back a couple days later, after it had hardened, and he carefully dug it out. And you can see, these were nightcrawler channels, all in in this one square foot area Interviewer: one square foot, yeah. Eileen: And you can see that basically those channels are going down, they've broken a little bit now in the meantime, but some of these channels were down three feet deep (okay). And just imagine water flowing across the surface and into these channels, how much water can flow down those big and deep channels (right), and they're very vertical. You can see that there, Interviewer: So you’ve got the vertical flow and then they have the chance to flow laterally as well? Eileen: Oh yes, yes, right. Once the water is down in the soil, it's going to move out from those. Interviewer: This is a fantastic illustration and this was taken on a farm field? Eileen: Yes Interviewer: WelI, I love this, it’s great. Eileen: Yeah right, yes, I think it's a great demonstration of nightcrawler channels.
3. Video: The Science of Soil Health: Compaction USDA NRCS (4:26)
- Click for a transcript of the compaction USDA NRCS video.
Interviewer: You know the plow seems to be symbolic of that can-do spirit that you find in American farmers. And so when you say that there may be better alternatives to tillage for compaction relief, that seems somehow counter-intuitive and almost un-American. I met two guys from Ohio State who use science to put conventional wisdom on its head. Alan Sundermeier: We're trying to tell the farmers that you cannot solve your problems with steel. You know, steel is shiny, you can put your hand on it. You can spend a lot of money on steel. And even with the subsoiler that may have minimal surface disturbance, it's really not solving the problem. You know, we're seeing that soil structure can be better solved by using natural rooting systems to their cover crops or continuous no-till from the cropping systems. And we have some other experiments here that are proving that. We have some compaction plots, comparing subsoil steel versus living cover crops. We're purposely compacting these plots in the fall, under moist soil conditions, by using a grain cart and going back and forth over the plots and forcing that compaction. And then the cover crops are planted, and then we're comparing that to using a subsoiler and our yields are showing better better results with the cover crops. And of course, when you get some heavy rains, you can see standing water problems, you know, that show up between the compaction levels of the plots, also that way. And the cover crops are outdoing the steel. Interviwer: So what's the explanation for these rather surprising results? Jim Hoorman: When, when you look at a soil, you have to look at the components. And the major component of most soil is sand, silt, and clay. Now that makes up about 45% of a really good soil. The other part of the soil, what we tend to forget about, is it should be pore space. Almost 50 percent of a really good soil is pore space. But then the most important part of a soil is the organic matter, that's like your head and your brains. That controls most of the chemical reactions and most of the life is with that organic matter. You know when you start to till a soil, what you do is you burn up the organic matter. So in the last 100 to 150 years, through tillage, we've lost probably at least 60% of our organic matter. Some studies say as much as 80 percent of the organic matter is going right up into the atmosphere. And this is a good area because this was the black swamp in in Northwest Ohio. When the first settlers came here, they said our soil was as black as midnight. And when you look at the soil now, you'll see that it's not as black. It's actually kind of a brown. It's lost its color, so it's lost a lot of its organic matter. I like to tell farmers that a lot of times, when you till the soil, you turn it into cement mix, okay, and so the soil gets very hard and dense. And one of the things that we've learned is, that if I was going to drill into cement, I would start with a small drill and then use a bigger drill to go through it. And so that's what we do with the cover crops. The cover crops actually have very fine roots and they form a small hole and then we follow that with corn and soybeans and those corn and soybeans will follow those same channels down through the soil. And they also follow earthworm holes, because earthworms are fairly big and they're also enriched with nutrients. And so those roots just really proliferate around those earthworm holes and that's how we then can actually loosen the soil up. Is it's the roots that loosen the soil up and give that carbon to the soil and also is a storehouse for all the nutrients in the water. Alan Sundermeier: So a lot of innovation is happening It's really an exciting time because farmers are seeing that there's different ways we can improve our soils by adding cover crops, you know, by not going to steel, by reducing our tillage. A lot of good innovative thinking I think has happened.