Paul McDaniel is Professor of Soil Science at the University of Idaho and an expert on what makes the soils of the Palouse so special.
What is it that makes the Palouse soils so special?
It mainly comes down to water holding capacity; and in this region, where we have very dry summers and growing seasons, the productivity is all about how much water the soil can store. These are very silty materials, and because of that, they hold a lot of plant-available water. So when we get some well-timed rains in the spring, the soils are charged up from the winter precipitation and over the course of the growing season they can provide an awful lot of water to the plants.
How did these soils get here? Weren't they blown in from elsewhere?
All this material was brought in a big dust storm, and so it just settles out of the air much the same way snow would fall. So it would be blanketed over the entire area. Some people have this idea of the sand dune type of topography, and it’s really a very different mechanism that has formed these types of hills.
Talking about misconceptions, one of the things you will commonly see in the descriptions of the Palouse is they talk about the dune-like topography; and people get the idea that these are all dunes. If you look at the material that make up the Palouse hills, it’s silt size. It’s down to the point where you can only see the largest silt particles with probably some magnification. They are fairly difficult to distinguish. If you were to do a laboratory analysis of what’s in the soil material, they maybe have 10% or at most 15% sand in most of the soils you would find around here, so very little sand content.
Some people have this idea of the sand dune type of topography, and it’s really a very different mechanism that has formed these types of hills.
But they do tend to be aligned according to the predominating winds. On the northeast side the hills tend to be steep, and then they are much less steep on the south slopes. And a lot of that has to do with what has happened since the material was originally deposited.
How unusual is that?
There are other areas in the world with loess. Probably one of the most famous areas is in China, what they refer to as the Loess Plateau; and that’s larger than the Palouse region. But certainly in North America this is the largest area of this type of a landscape and soils.
Is the soil as deep as some people say?
There are a lot of misconceptions about the soils inthe Palouse, which is interesting because it’s a region that is famous world-wide for the soils here. You see statements like the top soil is hundreds of feet deep, which just simply isn’t true, and particularly after farming, a lot of our top soils are either completely gone or mostly gone.
And the other thing that is real interesting is the way the Palouse landscapes have built up over the last two million years or so, with just successive events of the windblown material being brought in, and soils forming and then another cycle and another cycle. There are places where you can see twenty or thirty of these old soils just stacked up, one on top of the other.
If you went out into the core area in the Palouse and dug from the land surface down until you hit rock, there are places where you certainly could go a couple hundred feet. But I guess the point I was trying to make is that it really represents a stack of soils; and it’s a landscape that has built up over the last two million years or so by these successive depositions of the windblown material, then periods of stabilization where soil forms, and then probably related to the glacial cycles and inter-glacial cycles, and then you get another bunch of material blown in on top of that, just like a layer cake, really.
You say that the strength of this soil is its ability to hold water. Could you amplify on that a bit?
The silt particles are kind of intermediate. They are larger than clay particles and smaller than sands. When you get a soil made out of silt, the way the particles are fit together makes for a very extensive network of pores that can hold water. So typically, a soil like you see around here, maybe 20% of the volume would be water that a plant can access over the course of the growing season, and that’s pretty high. Compared to a real sandy soil, that number might be about 5%.
This soil is also very fertile, isn't it?
It is fertile, and I think the source of it is this ground up rock material from the glacial activity that took place to the north of us. And generally speaking, if you take fairly fresh geologic material, it is going to be fertile.
What has farming done to the Palouse soils?
Probably the biggest effect is that it increases the rate at which they erode. Erosion is a natural process, but when you come in and you disturb the natural vegetative cover, it just speeds up the rate at which the material is going to be removed.
People from the Midwest come out here, and they just can’t believe that people are going up and down these 25%, 30% slopes trying to farm them. That would be unheard of in the corn belt.
Unfortunately, some of the highest documented rates of soil erosion any where in the United States are from right here in the Palouse. I’ve seen estimates of something on the order of 200 tons per acre per year. It’s not that bad now. It really has improved with the adoption of conservation farming techniques and that sort of thing.
Why is erosion so devastating in the Palouse?
We have the silty soils, which are very subject to being eroded. We have very steep slopes which increases erosion; and one of the main crops grown around here is winter wheat. If you ever look at it during the winter time when we get most of our precipitation, it maybe is only a few inches up above the surface. It really doesn’t provide a lot of protection. So those three factors really combine to create a lot of potential for erosion.
And there have been estimates that even around here, some of the ridges may have lowered as much as six feet since settlement and cultivation. That’s probably an extreme case, but you don’t have to look too hard to find some areas where there has been fairly severe erosion.
I think there is much more awareness now of erosion, not just from the standpoint of losing the soil on a site, but the fact that this sediment that is lost ends up somewhere else; and whether it’s in a waterway or behind one of the dams on the Snake River, it’s going to cause environmental problems as well. So there is much greater awareness of it, and I think if you look at erosion rates in the Palouse today, they are considerably less than what they would have been fifty or sixty years ago.
Compare this region to other agricultural regions.
One of the biggest differences is just the slopes. People from the Midwest come out here, and they just can’t believe that people are going up and down these 25%, 30% slopes trying to farm them. That would be unheard of in the corn belt. Just having the kind of equipment to be able to negotiate a steep slope requires some technology that isn’t available in a lot of places.
Do you ever wish you could see what it must have looked like 150 years ago?
I guess when I look at it, you just don’t see areas where there are the deep silty soils that have not been cultivated, and it’s just testament to their productivity. Probably the only place you are going to find soil that approaches its natural state, or native state prior to settlement, would be in a cemetery or some place that has not been cultivated, for whatever reason. And up here, on Paradise Ridge, clearly it’s too rocky for cultivation to be practical. So we do have some very small, isolated areas of native soils, but I think the biggest difference is probably the vegetative cover and the Palouse plant communities.
How unique are these little remnants of Palouse prairie that have not been farmed?
These remnants are really one of the remaining vestiges of what the Palouse looked like. The fact is that most of these remnants were probably unsuitable for farming for one reason or another. They were either too steep or they are too rocky, like up here on Paradise Ridge. As a result, they weren’t cultivated, and even though the areas around them were, these have persisted as little islands of what was originally here. And the estimates are that certainly less than one percent of what was this Palouse prairie exists today, and you see it in these smaller remnants.
But these little remnants seem to matter to people, particularly young people.
I think you are right. It may be simply because of the realization there is so little of it left, and that is certainly one of the driving factors. I think the efforts we see at the community level and just the regional level for awareness of the Palouse prairie, a lot of this has come up within the last five to ten years.
And what about the interest in the giant Palouse earthworm? Does that surprise you?
The interest in the worm is something that has really amazed me. And I have been teaching an introductory level course in soil science, and you get a lot of students from different disciplines in there who really don’t have much interest in soils. But when the subject of the Palouse earthworm comes up, I see a lot of interest that isn’t there the rest of the semester.
It has just amazed me, and, in fact, after the article came out about Yaniria finding the worm over on Smoot hill, a number of students have asked me about it, even before I brought it up. That’s just very unusual for that sort of a course.
I think it’s great. I don’t normally think about an earthworm as being a very charismatic symbol of a region. It doesn’t have fur or brown eyes, but people really seem to have latched on to that.