 My name is Eugene Kelly. I'm a professor of pedology in the Department of Soil and Crop Sciences at Colorado State University. And our discussion today is going to center on soils and more specifically soil landscape relationships. What I'd like to do is to present this topic through the eyes of a pedologist. And our pedologist is somebody who studies soils and soil formation under different types of environmental conditions. And by doing so, in other words, understanding how soils form, we develop the capacity to predict how soils will behave when environmental conditions change. More specifically, I'll be looking at soil formation and soil properties as a function of landscape and topographic variations. Now, based on years of research in pedology and soil science, there are two fundamental things we know about soils. That soils first reflect environmental conditions and they also affect environmental conditions. This is called the duality of soil science. In other words, a soil reflects the environmental conditions under which it evolved. And that includes the climatological, geological, biological, and topographical conditions that generally define the state of the soil system. Secondly, soils affect the environment through the properties that are intrinsically native to the soil, again resulting from soil formation. These properties mitigate things like gas exchange, water content, and nutrient status and have a profound influence on the development of the soil and the ecosystem, and ultimately the productivity in natural and agricultural settings. So the soils of any region reflect environmental conditions, but they also affect environmental conditions. Now, as a pedologist, what we're going to do, we're going to study three basic components of pedology that will allow us to make this assessment of soils and environmental conditions as a function of topographic variations. What we're going to talk about first are the factors of soil formation, and then secondly, we'll talk about soil forming processes, or we refer to them as soil processes, and then finally we'll touch on some of the key soil properties. So we'll be talking about factors, processes, and properties. Understanding the relationship among the three of those groups is critical to evaluating soils through the eyes of a pedologist. First, we're going to discuss soil formation and the factors of soil formation. The factors of soil formation were first formalized by Han Jenny in his text in 1941. The text was entitled The Factors of Soil Formation. Now in this text, what Jenny did was he conceptually evaluated the mathematical relationships between soil properties and soils and what he considered to be controlling variables or conditioning variables. He later referred to these as state factors. He developed mathematical expressions that allowed any scientist or any person for that matter to evaluate soil properties in the context of these conditioning variables. In the text, Jenny expresses a mathematical relationship between soil and what he considers to be the state factors of soil formation. There is follows. The soil is a function of the climate, the organisms, the relief, the parent material, and time. And they're all symbolically expressed in this equation. The equation allows us to assess the variation in any of these conditioning variables and its impact on any specific soil property or ecosystem property for that matter. Now the application of the state factor theory is something we're going to address in the first part of this lecture. And what I would like to do is to kind of explain how this approach works. Essentially what you need to do is you need to assess a soil or soil property as a function of one of the conditioning variables. For example, climatological variables might be something like precipitation or temperature. Biological variables might be grasslands versus forests. So the equation allows one to assess the impact of any of these conditioning variables on a single soil property. So for the example that I'm going to use in this discussion, we'll be looking at soil, organic, carbon content. And we'll be looking at soil, organic, carbon content as a function of each of these conditioning variables basically to assess what the state of the soil system is. Now the first example I'm going to run through is looking at soil, organic, carbon, or what's just for that matter, let's just say soil as a function of climatic conditions. In the equation we see soil as a function of climate. And you'll note that the other variables are held inactive or relatively constant. Essentially what you need to do is you need to isolate the climatic variable, evaluate a soil property, and then vary climate to see what the impact of climate is on a specific soil property. For the examples, again, what I'll be doing is I'll be going through an evaluation of soil, organic, carbon accumulation as a function of each of the state factors. This equation expresses the soil, carbon, as a function of climatic variations. This is referred to as a climosequence. Now the first schematic shows us soil, organic, carbon content as a function of mean annual precipitation. And there are three platelets dealing with different soil textures. You'll note the platelet to the left looks at clay soils, the middle platelet looks at loam soils, and the platelet to the right looks at sandy soils. The relationships that are important here are as follows. If you'll note that organic, carbon content increases with increasing mean annual precipitation. In the first platelet, the clay soil, we see increasing carbon content with increasing mean annual precipitation. In a similar fashion, we see the same relationship with loam soils and with the sandy soils, increasing carbon content with increasing mean annual precipitation. Now in order to do this assessment, what you would need to do was to find soils within the same climatic region that varied as a function of texture and then move across precipitation gradients and evaluate the carbon content of these systems. Another observation of these data is that we look at rangelands versus cultivated in the same climatic regimes. In other words, evaluating clay soils that are under rangeland conditions versus clay soils that are under cultivated conditions. What you'll note is that both, in both systems, carbon content increases as a function of increasing precipitation. What's interesting to note is that this relationship occurs in the clay soils, the loam soils and in the sandy soils, but there appears to be a difference between rangeland systems and cultivated systems. This is an assessment of human impacts on soil formation and that is generally understood that cultivation induces carbon loss in most natural systems. So to note, we see the same increase in carbon content regardless of soil texture. This is an example of how climate conditions carbon content of soil. Again, all the other state factors in this example have been kept constant and these are data that are adapted from Burke in 1989. The other thing to note is that you'll see that the sandy soil has the lowest carbon content overall and the clay soils have the highest carbon content. The next example from Yanny's model is to look at a bio sequence. In this particular example, what we'll be looking at is the variations in vegetation type and the properties that they impart on the system, specifically again looking at soil carbon. On the Y axis, what we see is soil depth in centimeters and on the X axis, we see organic carbon content again in kilograms per square meter for three different systems. You'll note that the system to the left deals with short grass step vegetation and has about 5.7 kilograms per cubic meter of carbon. The Lodge pole pine system, the second platelet, has 4.8 kilograms per cubic meter and the alpine tundra has 18.1 kilograms per cubic meter. A very large difference in the amount of carbon stored in each of these systems as produced by different vegetation types. This is referred to as a bio sequence. In other words, the vegetation has a specific role in determining how much carbon is stored in the system. Now, if we take a closer look at these data, we see that the carbon content in the alpine tundra system is very high in a near surface environment and this is very typical of soils that we see worldwide. Carbon content generally decreases with increasing depth in the soil. The differences within the soil profiles in the short grass step and Lodge pole are not as dramatic. What we also notice is that the differences in the vegetation types impart very large differences in the total carbon stored. Much of this is related to the morphology of the plants. For example, in a short grass step ecosystem, we understand that at least half of the biomass is below ground, which would allow us to have more carbon storage in that particular system. In contrast, the system in Lodge pole pine has much of the biomass above ground, again resulting in lower carbon content in the soil, a relationship that's pretty clearly understood in Colorado for that matter. But the alpine tundra system is very, very different and that most of the biomass in this system is below ground, thus resulting in increased carbon content relative to most of the systems we observe in the Rocky Mountain region. The next example of any state factor approach we'll be looking at what we refer to as a lithosequence. In this particular case, we vary the parent material or the geologic substrate under which soil formation occurred and again we're going to evaluate soil carbon content. Now in this example, adapted from Aguilar in 1984, we evaluate three different parent material types sandstone, siltstone, and shales. And generally what we're doing is we're keeping all the other state factors inactive or constant. In other words, topographic variations are minimized, climatic variations are minimized, vegetation variations are minimized, and the time of soil formation is minimized. So what we're evaluating is the influence of parent material on soil organic carbon storage for three sites. What you'll note is that the shale site has the most organic carbon relative to the siltstone and the sandstone sites. You'll notice again that there's variation in carbon content within the soil profiles as a function of depth. In each and every system carbon content is highest near the surface and decreases with increasing depth. What you'll note and what's interesting in these particular data is that our most productive rangeland sites are actually the sandstone sites and they have the lowest amount of carbon storage. These types of relationships will be discussed later when we talk about processes that are important to carbon storage and systems. Another example of any state factor approach will be to evaluate time and its influence on soil formation. This is referred to as a chrono sequence where we look at a soil property again organic carbon as a function of increasing soil age. In this particular example adapted from merits in 1991 we have depth on the y-axis and organic carbon on the x-axis. We see five platelets that show us different age soils and the amount of carbon stored within each. What you'll note in terms of the general pattern is that the carbon content increases with increasing age going from 3,900 years old to 240,000 year old soils. Again carbon content increasing with increasing age in soil. Again this is an example of how time conditions organic carbon content similar to the fashion in which we evaluated climate, biota, and geological substrate. The final example that I'll show you of any state factor approach is to evaluate the influence of topographic variations on soil organic carbon content. These data adapted again from Aguilar in 1984 demonstrate variations in carbon storage within grassland systems as a function of differences in topography. In this particular example we see the summit which is the upland soils to the foot slope which is the lowland soils. Large variations in the total carbon stored. We see other landscape elements the shoulder and back slope are also increasing in carbon relative to the summit. In this particular case we see the same relationship that we see in other soils with organic carbon content. Organic carbon content highest in the near surface environment decreasing with increasing depth in the soil. What's interesting to note is that we have a gradual increase in the carbon content as a function of topographic variation going from the summit landscape position increasing slowly to the shoulder, back slope, and finally the highest amounts of carbon stored in the foot slope position. Now the topographic factor is important because it modifies other soil forming factors. In other words when we look at topographic variations we have an understanding that there are key processes that occur within the landscape that modify sediment movement, moisture movement, and in effect change the climatic conditions at each point along the hill slope. So what I'd like to do is to delve a little bit further into the topographic variations that we see along different gradients. Now using a model of the state factor approach we can evaluate topography by looking at differences in elements of landscapes. The model presented by Rui and Walker in 1968 demonstrates that we have different elements of landscape units that essentially are delineated based on discordance and slope. In this particular example we see the summit, shoulder, back slope, foot slope, and toe slope landscape elements. Each of these will be discussed in detail. The components of the hill slope are evaluated based on discordance and slope but also on the configuration of the slope. In other words the summit landscape position generally possesses linear slopes, has vertical water movement, uniform soil material, and is generally well-drained relative to other components within the hill slope. The shoulder is the more steeping convex component of the landscape where we have maximum runoff, soil, and subsurface water movement are very evident. The back slope are the more linear landscape positions within this hill slope and they have both surface and subsurface transport of water and some sediment movement as well. The foot slope is considered to be the more concave component of the landscape and it generally receives additions of moisture and sediment from upland positions. And finally the toe slope is the concave to linear portion of the landscape that is characteristic of depositional landscape elements in any region with accumulations of both organic and inorganic materials. Now the next schematic shows how topography modifies climatic conditions. In this particular example we see a hill slope cross section that looks at the summit, shoulder, back slope, foot slope, and toe slope landscape elements. Essentially this example adapted from Birkeland in 1991 shows us how the hydrologic regime at each of these landscape elements is different as a function of topography modifying precipitation. In other words each of the landscape elements receives the same amount of precipitation but topographic variations that induce runoff and runon conditions generally modify the effective precipitation that each of these soils will see. This is an example of how topography modifies precipitation. We understand that water movement on landscapes is governed by many fundamental controls. The water movement on landscapes integrates soils in different parts of the landscape through process and through property. The major variables that govern water flow on landscapes deal with extrinsic and intrinsic properties of the system. The extrinsic properties deal with things like rainfall duration and intensity and the intrinsic properties deal with things like soil texture, vegetation type, slope form and angle. What this tells us is how much topography and to what extent topography modifies other soil properties. So to summarize the state factors what we understand is that the properties of the total system or its component parts, the soil for that matter, are dependent on related to or conditioned by the state factors. In this particular case we're going to take a closer look at how topography conditions soil properties across different environmental gradients. The beauty of the state factor approach is that it provides a conceptual framework that allows us to evaluate natural and agricultural systems and the changes in conditions of soil formation and how these influence soil properties. Next what I'd like to talk about are soil forming processes. Soil forming processes can be lumped in the four categories. The first category are considered to be additions to the soil. The second category are considered to be removals from the soil. The third category of soil forming processes are translocations within the soils. And the final category of soil forming processes deal with transformations. So again we have four general categories in which we lump soil forming processes. Those processes which are additions, those processes which are removals, those processes which result in translocations and those processes which result in transformations within the soil system. So let's take a closer look at additions to the soil system. Additions to the soil system encompass both organic and inorganic materials. Organic additions to the soils are primarily the result of the death and decomposition of plant and animal remains. These are adding mass to the soil volume. Inorganic materials can be deposited both in wet and dry deposition and as a result of depositional processes within a hill slope. Removals from the soil are both in the form of solids, liquids and gases. Again solids would be both organic and inorganic materials and removals primarily consist of erosional processes. Liquids can be removed by leaching the soil through evaporation and transpiration processes and gases generally leave by diffusion. In other words in most soils concentrations of gases are higher than atmospheric conditions. CO2 for example, where the concentration is anywhere from 10 times to 100 times more than in the atmosphere. This results in the diffusion of CO2 out of the soil, again a loss of gaseous material from the soil. Translocations within the soil result in differences within a soil profile. Again this could be both with solid materials which encompass both the organic and inorganic compounds within the soil and also liquids in which dissolved salts are transported from one part of the soil profile and deposited in the other. Again translocations removing materials from one part of the soil depositing them in another. Organic and inorganic as well as dissolved constituents. The final general category of soil forming processes is encompasses transformations within the soil. These are both again organic and inorganic in nature. For example the transformation of organic compounds for example nitrogen which is 98 percent of which is in an organic form is transformed to the inorganic form through the process of nitrification. Again a transformation of organic to inorganic material mediated by microbial activity. Other types of transformations that occur in soil are weathering processes in other words taking a primary mineral like a feldspar weathering that transforming that to a kaolinitic mineral or a smectitic mineral depending on the environmental conditions. We also see transformations in the soil that are related to hydrological conditions and these are specifically mitigated by oxidation and reduction reactions. What I'd like to do now is to present the key soil and ecosystem properties that vary as a function of topographic position. Plant production, soil organic matter decomposition, erosion, deposition and leaching. These are all key soil forming processes that result in differentiation of soils across topographic gradients. In the first example on the platelet to the left these are data adapted from Schimel in 1985. We're looking at plant production as a function of distance from the summit. In other words on the y-axis plant production is in kilograms per hectare. On the x-axis we're looking at distance from the summit. We note that both above and below ground biomass increase with increasing distance from the summit. In other words when we go from the uplands to the lowlands we see generally an increase in the amount of above ground biomass that's produced as well as below ground biomass. Along with this relationship of a above ground and a below ground biomass what we note is an increase in the platelet to the right in the nitrogen mineralization along the same hill slope. In other words the uplands have lower mineralizable nitrogen than the lowlands. So key processes that are vital to ecosystems are varying across this topographic gradient. The following schematic shows the differences in leaching erosion and deposition across a hill slope. What you'll note from this example is that the soils in the uplands are generally immature, possess lower amounts of clay, have less leaching and less redoxomorphic features. As we move down the hill slope to the lower slope in the mid slope position what we note is that these soils have much more pedagogical development, higher amounts of clay accumulation, the possess greater amounts of redoxomorphic features, greater amounts of clay, suggesting that the weathering gradient is increasing from top to bottom along this hill slope. These are data adapted from Gerard in 1981. What we see is that the weathering process encompasses all of these leaching deposition and erosional processes. So the hill slope expresses differences in soil formation as a function of topographic position. Now what I'd like to do is focus a bit on key soil properties and how these vary as a function of topography. We have physical, chemical and hydrological properties that are basically conditioned by soil forming factors. What we're going to do is evaluate how topography conditions physical, chemical and hydrological properties within soils. Soil physical properties that are important to the management and sustenance of ecosystems are as follows. Soil texture provides a general information regarding the amounts of the sand, soil and clay size particles. We know that soil texture is conditioned by things like parent material and weathering. It is also conditioned by topography due to the result of erosional and depositional processes. A second property that's important to ecosystems is the soil bulk density which is just a measurement of the dry mass of the soil per unit volume. It integrates other key soil properties such as organic carbon, texture, organic matter, nitrogen and roots. All of these are important to determining what the bulk density of a soil is. Again, these types of properties are conditioned by these state factors. Depth to bedrock influences the depth to which roots can penetrate the soil. Again, topographic variations, parent material type have a profound influence on the depth to bedrock. Other soil physical properties that are important relate to the aggregate stability within the system which generally affects the soil by allowing water and air to move through the system freely. Soil color is also an important property of the soil that's related directly to topographic variations. We evaluate soil color looking at the U value in chroma utilizing one cell color charts and we know that the soil color reflects differences in organic matter content, salt content, oxidizing and reducing conditions. Again, each of these properties is intrinsically tied to topographic variations within systems. Soil chemical properties also suggest that topography has an enormous influence on soil formation and soil properties within a landscape element. Organic matter content as we suggested earlier is related to each of the conditioning variables of soil formation and tied intimately to topographic variations within a hill slope. We understand that organic carbon accumulation is the result of opposing processes, primary production and decomposition, the balance of which varies as a function of topographic variations as we pointed out in that Schimmel example earlier. Soil pH is another soil property that varies as a function of topographic variations. It gives us an indication of the acidity or alkalinity of the soil. It also gives us an assessment of the nutrient status since it's considered to be a master variable in terms of evaluating plant growth. Other chemical and properties that are important are the soil salinity which gives us an indication of the amount of salts that have accumulated in the soil. It links to processes of leaching, evaporation and transport and is related intimately with hill slope position. Cation exchange capacity gives us some indication of the nutrient retention capacity of the soil and is intimately related to weathering processes which again vary as a function of topographic variation. Not only is it weathering variations but also the transformations are primary to secondary minerals. Finally soil hydrological properties vary considerably as a function of topographic variations. Things like plant available water content which is just an index of the amount of water that's available to plant growth vary systematically along hill slopes. Infiltration rates again vary as a function of hill slope but other soil properties such as texture, coarse fragments and vegetative cover. Other hydrological properties that are important in evaluating hill slopes are permeability which is just the ability of the soil to transmit water and then water table depth which influences the redox relationships within a soil profile. So what we understand is that landscapes and landscape components display systematic differences in soil properties as a function of soil forming processes and we understand that the soil forming processes are modified by topographic variations. In other words topographic variations modify soil forming factors and result in unique properties within systems. The first example is to evaluate the position in the landscape and how this influences three key properties of the soil. In this particular example taken from Birkeland in 1999 we note soil depth on the y-axis and slope gradient on the x-axis. What we note is that the steeper the slope the less soil development. These data suggest that B horizon thickness is maximized where we have the lowest gradient of slope. We see similar relationships with the accumulation of bases in the soil noting that the depth to 80 percent base saturation is much deeper in the topographic position that has no runoff versus the landscape position that has maximal runoff that would be the back slope in this example. We also note that the organic carbon distribution in the soil is very different as a function of topographic variation. Increasing slopes generally result in lower water infiltration, more runoff and less carbon accumulating deeper in the profile. In this particular example the summit displays the greatest depth to one percent organic carbon among the three landscape elements because it possesses the lowest gradient of slope. Another example of a soil property that varies as a function of topography would be available water holding capacity. And what we note is a variation in this particular example between the summit and the foot slope. Along the x-axis we see the mean annual precipitation or the monthly precipitation as produced by Hannah in 1982. We note that in every case the foot slope possesses greater amounts of available soil water relative to the summit regardless of what the meteoric water conditions are. The next example of soil properties that vary systematically as a function of topography would be something like pH which again just gives us an index of the acidity or the alkalinity of the system. In this particular example we have a comparison of calcareous soils which are soils that possess calcium carbonate versus acidic soils which are generally soils that have low pH's and are depleted in base cations. What we note is in the calcareous soil that with increased gradient the pH of the system rises suggesting that we get less water infiltration, less weathering within each of these systems. In the acidic environment increased gradient results in a decrease in pH where we have less weathering the natural acidity of the system is not augmented by leaching or weathering processes. So in two different systems a calcareous system or an alkaline system versus an acidic system we see that the effect of gradient or slope gradient on the property is very very different. The next example from the literature suggests from Birkeland in 1999 suggests that water flow in the system determines the accumulations of basic cations and anions within the soil. In this particular example what we're noting is a soil solution concentration in milligrams per liter on the y-axis and then each of the anions and cations are grouped on the x-axis and what we note is that in each and every case the lower landscape positions maintain higher amounts of anions and monovalent and divalent cations suggesting preferential flow and water accumulation in these systems. Again you'll note that the back slope is actually lower than the summit or foot slope and the back slope is the more sloping landscape element higher gradients with regard to slope and thus more runoff. So in this particular schematic we see the foot slope accumulates most of the anions and cations the summit is actually intermediate and the back slope with a more sloping topographic position has the lowest amounts of anions and cations. In summary the degree to which soils and soil properties vary within landscapes is predictable and it's based on an understanding of the fundamental factors and processes of soil formation. Again the relationship between factors process and property and now what I would like to do is I'd like to take it four examples from the literature that look at soil formation and how conditioning variables affect topographic influences on soils. The first example is from a hot wet climatic condition in the southeast in the United States with a mean annual temperature of 66 degrees Fahrenheit and a mean annual precipitation of 45 inches. In this particular example what we note is variations in soil formation and soil properties as a function of topographic variations. In this particular example the upland soils which are plinthic candy udults in both cases, this is denoted by the blue and the gray outline on this particular figure, show that the soils are well developed and well drained. As we follow along the hill slope what we note is that the aqueous happily udults and the tippic candy udults are further downslope and receive moisture from the upland positions. Thus the aqueous subgroup suggests that these soils are wetter than the soils in the upland position. You'll note the depositional nature of this environment by the presence of the tippic quartzy salmons down in the lower landscape position. Again differentiation in soils and soil properties as a function of topographic variations. The upland soils possess soils that are well developed, well drained. The intermediate soils that are receiving moisture from the uplands are generally less well drained, in fact poorly drained with the presence of an aqueous subgroup and the lowest part of the landscape position we see depositional soils. Now if we look at topographic relationships under different soil forming conditions in this particular case a cold wet environment where mean annual temperature is about 50 degrees Fahrenheit, mean annual precipitation is about 120 inches. What we note are systematic differences in the soil properties as denoted in this cross-sectional figure. The bell grade, gloster and Paxton soils are all upland soils well drained, well developed. What we notice the bell grade is actually intermediate between the uplands and the lowlands and has an aqueous subgroup suggesting that this particular soil is affected by water table or sublateral flow from the upland positions. The sun, cook, awanda and winds of soils are all lowland soils. They possess weakly developed soil profiles suggesting that deposition of material from the upland positions. Again weakly developed soils in the depositional landscape positions well developed soils in the upland more stable positions topography imparting its influence on soil properties across a very large area in this particular case again a cold wet environment. The next example from the literature looks at the depositional nature of landscapes looking at a cold dry environment and this is an example from the Bitterroot Valley in Montana. Mean annual temperature is 46 degrees Fahrenheit, mean annual precipitation is 15 inches. What we note is that there are fundamental differences in the soil properties as a function of landscape position. You'll note that the calcic haplocryols, the xerolic nature arches and the calcic haplocryols all occur in the lower landscape positions. Each of these soils accumulates key soil components for example the xerolic nature arches accumulate large amounts of sodium whereas the calcic subgroups and the haplocryols accumulate calcium carbonate. These landscape elements receive material from the upland positions which are the tippic cryocreps and the tippic haplocryols as well as the mountain lands. In each and every case the low lying positions in this particular region are more well developed because this region is limited by precipitation. In other words topography imparts its influence by looking at differences in soil age as a function of topographic variation not necessarily the distribution of water. We can have dry input of calcium carbonate, sodium and other salts which again would impart differences in soil properties. The final example that I'm going to show you is from a hot dry environment in New Mexico with mean annual temperature of 62 degrees Fahrenheit and the mean annual precipitation 12 inches. In this particular case what we note is large variations in soil properties as a function of topographic variations. The Simona, Potter and Bipus soils are all located in what we would consider to be upland positions. In each and every case these soils are the most well developed. In other words they're unstable uplands and possess horizons that are solidified. For example the Simona is a tippic petrocalcid which suggests that the soil has been stable for many thousands of years. The Potter and Bipus soils are the same. We note that the Largo and Pajardo soils or the tippic capital canvads are located in the lower landscape position. In each case these soils are weakly developed and possess no diagnostic features that suggest that topography modifies soil formation. Again in hot dry environments it's not necessarily the modification of water across these landscapes what we're looking at is different soil ages as a function of topographic position. The older landscapes possess soils that are well developed, the younger landscape possess soils that are weakly developed. In summary the need to understand the distribution of soil properties and soil behavior is indeed imperative to the management of both natural and agricultural systems. Landscape units display systematic variations in soil properties as a function of relief modifying other soil forming processes for any individual reason. So now you're viewing the soil as a pedologist and as a pedologist what we understand is that we try to relate soil forming factors to soil forming processes to soil forming to soil properties. Again factors condition processes which result in unique properties. What I hope to cover today was to show you that topographic variations have a profound influence on soil properties and the influence varies as a function of the other conditioning variables. For example climatic variables, geological variables and biological variables. Thank you.