Soils Primer Part 4 Transcription PDF

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Soils Primer Part 4 Transcription Slide 1: Soil physical properties, as opposed to soil chemical properties, is coming up in the next segment. We've got some terms here. I'm going to list them, and then we'll go through and we’ll define them. The different properties are texture, structure, color, permeability, and of these, the most important in terms of growing turf, maintaining turf, is texture, structure and permeability. Color, an indicator oftentimes of the para material that was the soil that it is being formed from, and/or the amount of organic matter, and/or the amount of clay that's in the soil. Slide 2: Soil texture. That's relative amounts of the following soil particles, and there's only three types of mineral particles found in soil, and we're going to classify them by size. There's sand, sand being two millimeters in diameter down to five hundredths millimeter in diameter. Anything above sand would be gravel. Then you have silt. Silt picks up where the size of sand, it gets too small to be calling it silt, from 0.05 hundredths down to two thousandths of a millimeter in diameter. So, we're getting very small here. Then finally, clay. Clay particles are extremely small. There's really an increase in magnitude here from this difference here. Okay. I'll give you a little analogy here that is used. I'll give you two of them. The first one I'll give you, because many times you visit Washington, D.C., and say you're in your car, and you have a little brochure, a map how to get around, and say you’re driving around the U.S. Capitol Building. Well, the Capitol Building you could think would be analogous to a grain of sand. Then the car, relative to the size of the sand, the car could represent a silt particle. So, you can see a big difference there. Then, on the dash might be this little, thin map or brochure, and that would be analogous to a clay particle. Think how many brochures you could pack into your car and then how many cars you could fill into the Capital Building. You get an appreciation for the extreme differences in size of these three soils, mineral particles that we have, sand, silt and clay. Now, there's another analogy that I learned later on, since I came to MSU. You have a room, say your classroom or the room that you're in. Okay, the room you're watching this in. And you fill it with beach balls. Okay, fill it completely full of beach balls, and that would be as much sand as you could get in this room or this unit area, this unit volume, rather. So, you've got it packed full of beach balls. And then you take golf balls, or maybe ping pong balls, something that size, and then you pack them in there, and they work their way down, and you try to pack it all through with ping pong balls or golf balls, whatever it is. Pack 'em in there, and there'll be a lot that can fit between these beach balls. Okay, and those would be silt particles. Then if you were to take very small bb’s or

very, very small anything, really. And then if you put that in there, set it down in there, that would be your clay. So, that'd be a relative way to appreciate the relative size differences among soil particle classification types. So, let's go back and look at that further in the slides. Slide 3: As far as this goes, just need for you to know which is the largest, which is the smallest, and the fact that there's great differences between these sizes. Extreme differences. Slide 4: Now, here's something that everybody with a soils class has ever seen. This is what we kind of use. We'll talk about different types of soils, but just to maybe give you just kind of a talking point here. This is a soil triangle. You would get an analysis of the amount of sand, silt and clay in a percent basis on the bottom of the triangle, moving from greatest, from least to greatest across here. Silt, the next order to size coming down, and clay going up. So, say you have, maybe we've all heard about a loam, a loam being a very, it's friable, desirable soil that contains sand, silt and clay. This right here, we look right in the middle of the loam would be 60% sand. And that comes down and then you have percent silt that goes up here to 40% like this. This loam here, actually how you read this thing is off the angle here, so this would have 40% sand, 40% silt and 20% clay. So, that adds up to a hundred. So, that would be a loam, and the more you increase clay content, you get to have a clay loam. Increase silt, silty clay loam, and differentiation soil types here. Any time really, except for the extremes here, you get above 40% and 50% clay, you just call it a clay. Now, we'll talk a lot in here about sandbased systems or high-sand root zones, and these are manufactured, engineered root zones. They use screens and they mix them in different size particles. But we talked about that. We talked about a sand, a sand. Well, a sandy root zone. Well, boy, look here. A sand really starts down here. A true sand at about 84% sand, you'd have to have for this part here, 84% to 90% in here would be a sand. So, when we talk about a highsand root zone, we’re talking about something that has very little silt and clay. I'm not going to ask you to de-place these here, but this is something that you'll run across, and if you were to get a texture analysis, which is you take a soil sample, send it in, and they'll send you back the relative amounts, and they'll also do this classification for you. But this is where it all comes from. Slide 5: Now, soil structure, ... it's the arrangement of aggregates. Well, over time in the weathering process and with the presence of organic matter, these acids and other organic compounds, will help the soil, smaller particles to group together or aggregate. And these aggregates become even much larger than sand particles. Sometimes they don't even contain sand. But that would be like if you were take this room, if this room was a garage, and say you drove two cars into it and then you put in beach balls and ping pong balls and bb's, ... then these aggregates really have a strong influence on

how the arrangement of everything, as it affects porosity, as we're moving too quickly here. So, that's soil structure, and let's look at some examples here. Slide 6: [clumps of soil] Here you see these crevices and things like that, and these clumps of soil here and clump of soil. And maybe here, even here and here. Aggregated together, you're going to see little fissures. And this is an indication of a soil with very good structure. Structure takes a very long time to develop, and it can be destroyed... very quickly with excessive tillage or excessive plowing, or in our case, if you're under an establishment, if you were to rototill this too much into just a fine powder, you'd destroy aeons, or at least centuries of weathering, which creates structure. All right, so soil structure. Slide 8: Soil structure, we talked about porosity. Try and tie this all together. And porosity, the degree to which this soil mass permeated with voids or cavities. Then these things can be occupied by water and air. Remember we said about half the soil is water and air. Well, you have to have spaces for the water and air to occupy. Slide 9: So, what's a soil pore? Well, a skin pore would just be an opening on the skin, and plant leaves have pores. But, with soil, we're talking about holes, or really little spheres, or whatever the shape may be in the soil. The larger ones are called macropores. And macropores are contiguous. It means they border each other. There's that word again. And this provides channels that where water can infiltrate and continue to drain out, and also air can move in there. So, this really lends itself to that 50% air, water model that we saw at the start of this presentation. Versus micropores are relatively small. They're very small, and they're so small that they’re not connected. So, this means that they don't have typically good drainage, but then, on the other hand, because water doesn't drain out of them readily, water can be stored in there, and to a certain extent, this water can be taken up by the root hairs. Slide 10: [micrograph of a soiled pore] Here's a micrograph of a soiled pore. Here you have the one that, you might say, is more spherical in shape. But, right here there's one that's kind of connected here, formed over time. What formed that, freeze, thaw will do it. This may have been a place where a root was growing at one time, and then the root died, decomposed, and left this void here, this very large macropore. Slide 11: [photograph of clay soil] Okay, here you see, this would be a situation where a clay soil, that the shrink, swell of these. We call them smectite clays, where, as they dry out, you'll see these cracks. Hey, the water goes right in there. Air goes right in there.

Slide 12: Back to porosity. Very much affected by soil texture. Sands have the greatest number of macropores. Okay, if we fill this room with just beach balls, think how much of the volume is not occupied by beach balls. Clays have the greatest number of micropores. Okay, we pack this room, instead of with beach balls, we pack it full of golf balls, some of it's going to be isolated and really, and they seal off, and maybe that's not a good analogy, because clays have different shapes. But you'll have these micropores formed. So, sands have the greatest macroporosity, clays have the greatest microporosity. And those are the two extremes, and we’ll build from there. Macroporosity also affected by soil structure, certainly. Structure is what we have to maintain. We're going to do everything we can to increase the soil structure over time. And then we're going to manage the soil. It would be a good soil husbandry to try to keep the greatest amount of macroporosity as we can, and that's a key thing, because if you just get down to all micropores, the soil, they're compacted. Water can't infiltrate. Air can't get in there. They become water log compacted. And they're not good for growing turf. So, when we're managing our soil, we want to increase macroporosity and maintain our structure....