Purdue Agronomy Soil Monoliths Demonstration


We’re actually going to look at some soil monoliths live here. We have a collection of probably 10 or 12 soil monoliths on this cart. What you notice about these monoliths is this range in soil colors that we have. We have black soils, sort of brown soils, we have gray soils, we have red soils, we have white soils horizions. We have a whole range of different colors and soils profiles. I think people have a tendancy to look at the top of the soil. All they see is something that is dark brown or black and they think that all soils are just black or dark brown. When you cut into the soil and see that verticle variability, you are going to see a wonderful array of colors. That is what gets me really excited about soils. I just want to point out a few horizions to you, we talked about it in the PowerPoint presentation, and I thought I’d point them out to you with some real soil profiles. We’re going to start off with a forested profile. Yesterday we talked about forested soils having “A” horizions, “E” horizions, “B” and “C”. What differientiates a forest soil from a prairie soil is the prescence of an “E” horizion. In this particular profile here on the far end, we have an “A” horizion, a nice leach bleached “E” horizion, then an accumulation of the humus and the iron down here in what is called the “BHS” horizion. This horizion right here would be the “BS” horizion and down at the very bottom we are down into the parent material or the “C” horizion. This profile right here, happens to be in my mind one of the pretiest soils that you will ever encounter out in the landscape. We find these types of soils with these really well developed “E” horizions when we go down to Florida. We often think of Florida being beach sand, but when you get into the inland areas a little bit and you dig down into the soils you are going to find wonderful soils that look like this. Now, we also have, if we look at forested soils here in Indiana. Our “E” horizions are not quite as developed as in Florida. So what we find is that we have a nice “A” horizion, we have a very small “E” horizion. Remeber we talked about the Munsell color code system, it has a little higher value. We have an “A” and “E” maybe a transition zone, a “BE” or an “EB” and then down here is the “B” horizion. Remeber yesterday we talked about “T” the accumulation of clay. This is where “BT” would come into play here. Subhorizion designation “T” meaning an accumulation of clay. Down here is the parent material. If we look at a prairie soil, prairie soils are completley different. Prairie soils have no “E” horizions. So we have a nice “A” horizion here, then it transitions into a “B”horizion. You probably do have a transition zone here, could be an “AB” or “BA”, those are transition layers. Then you got down here a “BT” probably and a “C”. Again what differientiats a prairie from a forest soil is the presence of an “E” horizion in a forested type of soil. We also talked about the difference between organic matter and humus. Organic matter is recognizable out in the field. The very top of this soil profile right here, you see this sort of stuble residue type material. That is organic matter. What happens over time, is the microorganisms decompose that organic material. What happens is that you end up with humus. Humus is actually the component of soil that give you tilth, that give you cat ion exchange capacity, gives you water holding capacity, give you nutrient supplying capacity in the soil. We can look at all these monoliths, they are really wonderful to look at and I always really enjoy this at the beginning of class. The first section is soil differences and I have students looking at different profiles. What they see is all these dramatic colors. How you can use colors to help you differentiate soil horizions. Subtitles by the Amara.org community

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