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Manual 6 • Reprinted September 2007 $12.50

MANUAL FOR JUDGING OREGON MANUAL FOR JUDGINGJUDGING OREGON SOILS

OREGON STATE UNIVERSITY EXTENSION SER

VICE Contents i

Chapter l Why Study ? ...... 1

Chapter 2 Factors of Soil Formation ...... 4 The Soil We Study Processes of Soil Formation...... 6 From Rock to Soil ...... 7

Chapter 3 Master Horizons ...... 9 Kinds of Soil Horizons Special Kinds of A, B, and C Horizons ...... 10 Transition Horizons ...... 12 Subdivisions of Thick Horizons ...... 13 More Than One Kind of Parent Material...... 13 Typical Horizon Sequences ...... 14 Locating Boundaries Between Horizons ...... 14

Chapter 4 Color of the Soil Matrix ...... 15 Properties of Soil Horizons Mottling ...... 17 Texture ...... 18 Coarse Fragments ...... 23 ...... 25 Soil Consistence ...... 28 Horizon Boundaries ...... 29 Special Features of Soil Horizons ...... 30

Chapter 5 Effective Depth of Rooting ...... 33 Properties of the Whole Soil Available Water-Holding Capacity ...... 34 Permeability ...... 36 Water Hazard ...... 39 Wind Erosion Hazard ...... 41 Internal Soil Drainage ...... 42 Color Plates ...... 47

Chapter 6 Landform ...... 51 Site Characteristics Parent Materials ...... 54 Stoniness and Rockiness ...... 57 Slope...... 58 Aspect ...... 59

Chapter 7 Feasibility of Artificial Drainage ...... 61 Management Interpretations Suitability for Irrigation ...... 63 Most Intensive Crop ...... 64 Practice ...... 70 Reaction Correction ...... 73 Limitation for Septic Tank Drainfields ...... 74

Appendixes A. How to Use Interpretation Guides ...... 79 B. How to Set Up and Run a Soil Judging Contest ...... 81 C. Horizon Names Used Before 1983...... 85 Glossary ...... 87 Scorecard...... 95 Interpretation Guide ...... 97 ii Foreword

oil judging has been part of the important aspects of soil behavior, vocational agriculture curriculum in such as effective depth, water-holding SOregon high schools for more than capacity, susceptibility to erosion, and 40 years. Since 1956, the OSU Extension internal drainage class. Service and the Oregon Association of 4. We explain why soil properties and Districts have worked behavior are important to soil manage- together to organize and operate the State ment. Soil Judging Contest. 5. We develop keys for students to use to The Extension Service also has pro- relate soil properties to important vided educational materials for the stu- decisions about irrigation suitability, dents and conducted training sessions for crop choices, erosion control, and the instructors. For many years, Exten- other questions. sion Bulletin 769, Soil Judging from the We don’t expect students to memorize Ground Up, was used as the primary text all the factors and interactions that enter for the program. into a management decision. We do hope, As we learned more about Oregon soils, however, that they will learn how to use however, and as alterna- the keys to translate their evaluations of tives became more complicated, we profile data into solutions to real prob- realized that just revising EB 769 would lems facing modern agriculturalists and not do the job. Instead a completely new environmental scientists. manual was needed. Above all, we view soil judging prima- We began writing a new soil judging rily as an educational program. Contests manual, and developing a new format for certainly add a dimension of challenge judging soils, in 1978, when we introduced and fun, but they are not the primary several new ideas to a group of about 20 objective of the program. Instead, the Vo-Ag instructors. They liked the new main objective is to encourage students format, and their comments were very to investigate this fascinating resource we helpful as we wrote a draft of a new call soil, to discover how soils are orga- manual. We used this draft for 4 years while nized into horizons, to learn both how to we tested new ideas and revised the text. describe a few key properties of soil Publication of this manual would not horizons and to interpret them in terms of have been possible without numerous management practices—and to develop a suggestions from many soil scientists and sense of stewardship for the soils that Vo-Ag instructors who have been very support them. closely associated with the soil judging Nothing would make us happier than program for a number of years. To each of for a student to challenge some of the them, we express our sincere apprecia- generalized management interpretations tion. we describe in this manual in terms of There are several major changes in this their relevance to his or her own soil new Manual. conditions—and for the instructor to 1. We encourage students to study the seize that opportunity to do some real whole soil profile and evaluate each of teaching about the kinds of interactions the natural soil horizons present. one must consider when deciding how 2. We stress gathering primary data on best to use the soil resources available on just a few important properties that a given farm. When this happens, the students can determine in the field— Manual for Judging Oregon Soils will have color, texture, and structure. accomplished its real purpose. 3. We show students how to use these basic properties to discover some Chapter 1 1

Why Study Soil?

oil is an essential natural resource. alfalfa hay and range grasses, we process Without a doubt, that is the most through livestock first. Even the fish we S important reason for studying the eat depend on plants that grow in the sea soil. Nathaniel Shaler put it this way: “Soil, using nutrients that have been washed out ever slipping away in streams to the sea, of the soil and carried to the sea in rivers is a kind of placenta that enables living and streams. things to feed upon the earth.” We study the soil, then, to increase our The sketch in Figure 1 illustrates our understanding of this resource that sup- dependence on the soil. Unlike plant life, ports us. we human beings can’t manufacture our Another important reason for studying own food from the four primary resources soil is that soils are different. Oregon alone of soil, air, water, and sunlight. Instead, we has nearly 2,000 different kinds of soils, depend completely on green plants, which ranging from deep to shallow, clayey to take nutrients and water from the soil and sandy, wet to dry, nearly level to steeply combine them with air and sunlight to sloping. These differences are important, provide our food supply. because different soils require different Some of those plants, such as wheat kinds of management practices. and corn, we eat directly. Others, such as Wet soils, for example, are essential components of wetland ecosystems. Proper management of wet soils depends 1Shaler, N.S., Man and the Earth (Chautauqua, on recognizing the imprint of saturated NY: The Chautauqua Press, 1915).

Figure 1.—All of our food resources can be traced directly back to the soil. 2 Chapter 1 • Why Study Soil?

conditions on soils and maintaining water morphology. Some properties, such as tables at desired levels. color and abundance, can be deter- Many soils require irrigation for maxi- mined by eye. Others, such as texture and mum productivity. Both the amount of structure, require a keen sense of touch. irrigation water needed and the proper You, too, can learn how to determine method of applying it depend on a soil’s the important properties of soil horizons. permeability rate and water-holding Then you will be able to make a number of capacity. important decisions about drainage, Still other soils have a very serious irrigation, crop selection, erosion con- erosion hazard. The proper choice of trol—and much, much more. conservation practices depends in part on At the beginning of this chapter, we the texture of the surface horizon and the talked about how all human life depends steepness of the slope. on our soil resources. Knowing that, we Only by studying soils can we learn how must study the soil so that we can learn to tailor management practices to the how to protect it for others to use. There’s specific needs of each of the many differ- plenty of good soil on this planet—as long ent kinds of soils we depend on. as we take care of it properly. But if we let Some of us study soil because we’re just it erode, or compact it, or mine it, it will plain curious about this unique and fail to support us. fascinating natural resource. When you Farmers are the primary stewards of the dig a hole or scrape off a road cut, you soil, for they are the tillers of the land. All discover right away that there’s a whole of us, however, share the responsibility to lot more to the soil than just the top 8 or protect this valuable resource. If we 10 inches. manage our soil properly, it will continue Soil scientists, in fact, study the soil to a to nourish us for generations to come. If depth of about 5 feet. They see several we don’t, our very civilization is threat- different layers, or horizons, in the soil. ened. Together, these horizons make a soil So study the soil, learn about its proper- profile. ties and behavior, manage it wisely, and We describe the horizons in a soil do your part as a steward of the land. profile in terms of their properties, or Chapter 2 3

The Soil We Study

oil has been defined by lots of differ- the winter to very dry in the summer. ent people in lots of different ways. Even under irrigation, the amount of S Here’s a very basic definition: water in the soil can vary widely. Soil increases when crop SOIL—the natural medium in residues are worked in, and decreases as which plants grow. fresh plant materials decay. Soil nutrients This definition, however, may be a little increase as soil minerals break down. too simple. Here’s a better one: They decrease as water moving through the soil carries them away. Even soil SOIL—a natural body that devel- acidity, or pH, changes seasonally. ops in profile form from a mix- The word system says that all parts of ture of minerals and organic the soil work together to make up the matter. It covers the earth in a dynamic whole. A change in one part may very thin layer and supplies cause changes in many other parts. plants with air, water, nutrients, Suppose, for example, we add water and mechanical support. until the soil is very wet. That reduces the Our definition is, of course, the one we amount of air available to plant . It prefer: makes the soil colder, and the activity of SOIL—a living, dynamic system at roots and soil microbes (very small plants the interface between air and and animals) slows down. The wet soil is rock. Soil forms in response to stickier and cannot bear as much weight. forces of climate and organisms that act on parent material in a specific landscape over a long period of time. We like this definition because each key word says something important about the soil. Why living? Because the soil is full of living organisms: roots large and small, animals and insects, millions of micro- scopic fungi and . Equally important are the decaying remains of plants and animals after they die. They form , or , which is vitally impor- tant for good soil tilth and productivity. Dynamic says that the soil changes all the time. Oregon Figure 2.—Living, dynamic soil. The microscopic worm shown is called a soils change from very wet in nematode. The lower part of the nematode is being attacked and invaded by a . 4 Chapter 2 • The Soil We Study

Now let’s remove the excess water. The topography, and time, are called passive whole system changes to a warmer and factors. They respond to the forces drier soil that is better for plants to grow exerted by climate and organisms. in and easier for farmers to manage. Together, the interactions between the The word interface stresses the idea force factors and the response factors that soil is indeed a very thin rind at the result in a new product, a unique natural earth’s surface. When air meets rock, resource, which we call soil. especially if the air is warm and the rock is moist, the rock begins to change. Some Climate changes are physical. They break rocks Climate affects soil most directly down into smaller pieces. Other changes through temperature and rainfall. In are chemical. They destroy some of the warm, moist climates, rocks and minerals original minerals and create new ones. weather very quickly. The soil that forms These physical and chemical changes often has a reddish color. Most of the red are called . Weathering occurs soils in western Oregon are red because only within the first few feet of the earth’s they formed when the climate was surface. Plate 5 illustrates a strongly warmer than it is now. weathered soil. The light-colored parts of High rainfall also causes —the the BC horizon are highly weathered removal of soil materials by water flowing remnants not yet fully changed through the soil. Free lime is completely into soil. leached from western Oregon soils. These Now consider the size of the earth. The soils are acid. Free lime is still present in distance from the surface to the center of many eastern Oregon soils because there the earth is about 4,000 miles. Thus, 10 feet of weathered rock out of isn’t enough rain to leach the soil com- 4,000 miles is something less than pletely. .00005 percent. Soil does indeed occur at Warm, moist climates encourage lots of the point of contact between earth and plant growth, and that means lots of soil atmosphere! organic matter. The opposite is true in hot, dry climates. Soils in the Willamette Valley are dark-colored because they have Factors of Soil Formation plenty of organic matter. Soils in the The rest of the key words in our defini- Ontario area are light-colored because tion of soil tell us something about how they have very little organic matter. soil forms. We think in terms of five soil-forming factors. Two of them, climate Organisms and organisms, are called active factors. Organisms are of three general types: They provide the forces that cause soil to large plants, tiny plants (microbes), and form. The other three, parent material, animals. Roots of large plants help break rocks apart and mix soil particles. Root channels provide pathways for water and Five Soil-forming Factors air movement through the soil. Above- ground plant parts die and decay, thereby Climate building up the organic matter in the soil. Organisms Microscopic organisms, or microbes, Parent Material are an extremely important part of the Topography soil. They are the primary decomposers. They change raw plant material into a Time complex black substance called humus. At the same time they release soil nitrogen, Factors of Soil Formation 5

an essential nutrient that plants need in large quantities. Thus, rich, fertile are rich and fertile because they are well supplied with humus (see Plates 3, 4, and 8). Even the earthy smell of moist, rich, is caused by a microorganism. Microbes and the humus they produce also act as a kind of glue to hold soil particles together in aggregates. Well- aggregated soil is ideal for providing the right combination of air and water to plant roots. Without microbes, therefore, soil would be a virtually inert (lifeless) body. With them, soil is truly a living, dynamic sys- tem. Soil animals include large burrowing Figure 3.—Humus formation. Strands of fungus surround a animals, small and insects, freshly clipped blade of grass. Decomposition is beginning and microscopic worms called nema- and will soon convert the clipping to soil organic matter. todes. All are important because they help mix soil. Animal mixing carries raw plant debris that lies on the soil surface down influence of parent material is not as into the topsoil. Only then can the evident. microbes do their job of changing plant As soils age, many original minerals are material to humus. destroyed. Many new ones are formed. Soils become more leached, more acid, Parent material and more clayey. In short, the soil becomes more strongly developed with Parent material is the original geologic the passage of time. material that has been changed into the soil we see today. Parent material is Topography passive because it simply responds to the changes brought about by weathering and Topography, or landscape position, biological activity. causes localized changes in moisture, Many parent materials are some kind of temperature, and parent material. When bedrock, like or basalt. Others rain falls on a hillslope, for example, water are deposits of carried by runs away from the top of the hill. Excess water, wind, or ice. Volcanic ash, lake-laid water collects at the bottom of the hill. , dune , and glacial all are Soils at the top of the hill are relatively examples of transported parent materials. dry and often show the effects of erosion on the soil profile. Soils at the bottom of Time the hill not only are wetter but often are formed in materials transported down Time is the great equalizer. Young soils slope and deposited in lower landscape inherit the properties of their parent positions. materials. They tend to have the same Another effect of topography is due to color, texture, and chemical composition the direction that a slope faces. Soils on as their parent materials. Later on, the north-facing slopes, for example, tend to be cooler and wetter than soils on south- facing slopes. 6 Chapter 2 • The Soil We Study

Processes of Soil Formation Many fertilizers, especially nitrogen fertilizers, also are quite soluble. They, Our definition of soil has identified five too, are readily lost by leaching, either by factors of soil formation. We also can think natural rainfall or by irrigation water. in terms of four major processes that Other minerals, such as and change parent material into life-sustaining sand grains, dissolve very slowly. They soil. They are additions, losses, transloca- remain in the soil until it is very old and tions, and transformations. highly weathered. Losses also occur as gases or solids. Oxygen and water vapor are lost from soil Processes of Soil Formation as fresh organic matter decays. And when soils are very wet, nitrogen can be Additions changed to a gas and lost to the atmo- Losses sphere. Solids are lost by erosion, which removes both mineral and organic soil Translocations particles. Such losses are very serious, for Transformations the soil lost by erosion usually is the most productive part of the soil profile. Additions Translocations The most obvious addition is organic Translocation means movement from matter. As soon as plant life begins to one place to another. Usually we think of grow in fresh parent material, organic movement out of a horizon near the soil matter begins to accumulate. Organic surface and into another horizon that is matter gives a black or dark brown color deeper in the soil. to surface soils. This is why even very In low rainfall areas, leaching often is young soils usually have a dark-colored incomplete. Water starts moving down surface layer. through the soil, dissolving soluble miner- Other additions come with rainfall. On als as it goes. But there isn’t enough water the average, rainfall adds about five to move all the way through the soil. pounds of nitrogen each year to every When the water stops moving, then acre of soil. Rainfall also can be acid, evaporates, the salts are left behind. especially downwind from industrial That’s how accumulations of free areas. Acid rain may change the rate of lime are formed (Plate 9). Many some soil processes. Rainfall, by causing in soils of dry areas form this way, too rivers to flood, is indirectly responsible (Plate 10). for the addition of new sediments to the Upward translocation also is possible. soil on a river’s floodplain. Even in the dry areas of eastern Oregon, there are some wet soils that have high Losses water tables. Evaporation at the surface causes water to move upward continu- Most losses occur by leaching. Water ously. Salts are dissolved on the way, and moving through the soil dissolves certain left behind as the water evaporates minerals and carries them out of the soil. (Figure 4). Salty soils are difficult to Some minerals, especially salt and lime, manage, and they are not very productive. are readily soluble. They are removed Another kind of translocation involves very early in the history of a soil’s forma- very thin particles. Water moving tion. That’s why soils in humid regions through the soil can carry these particles don’t contain free lime. from one horizon to another, or from place to place within a horizon. When the From Rock to Soil 7

water stops moving, clay particles are of the soil is gray because of loss of iron, deposited on the surface of soil aggre- and part is yellow-brown where the iron gates. We call these coatings clay skins, oxides have accumulated in localized and they have a dark, waxy appearance areas. (Plate 15). From Rock to Soil Transformations How do all these processes work These are changes that take place in the together to form soil? Let’s start with a soil. Microorganisms that live in the soil fresh parent material. Climate starts acting feed on fresh organic matter and change it on it immediately. Weathering begins to into humus. Chemical weathering changes change minerals. Leaching removes salts, the original minerals of parent materials. then free lime. Some minerals are destroyed completely. As soon as plants begin growing, they Others are changed into new minerals. add organic matter to the soil. Biological Many of the clay particles in soils are activity increases, and humus forms. Soon actually new minerals that form during a dark-colored surface horizon is present. soil development. Weathering and leaching continue to Still other transformations change the change soil minerals and remove soluble form of certain elements. Iron components. More horizons develop usually gives soils a yellowish-brown or beneath the surface. The soil becomes reddish-brown color. In waterlogged soils, more acid. Clay minerals begin to form. however, iron oxide changes to a different Clay is translocated and clay skins become form that we call reduced. Reduced iron visible. oxide is lost quite easily from the soil by As the amount of clay in subsoil hori- leaching. After the iron is gone, the soil zons increases, the rate of water move- has a gray or white color. ment through the soil decreases. Weather- Repeated cycles of wetting and drying ing continues, but leaching isn’t as rapid. create mottled soil (Plates 7 and 16). Part After a while, further change is very slow, and the whole soil-plant- landscape system is in a kind of steady state. How do we know that all this has happened? First, we dug a hole to reveal a soil profile. Next, we studied the soil carefully, located the horizons, and determined their proper- ties. Then we interpreted the information from the profile in terms of the factors and processes of soil formation. You, too, can learn how to describe and interpret soil Figure 4.—Upward translocation. The white areas, called profiles. That’s what the rest of slick spots, are accumulations of salts left on the soil this Manual is all about. surface after water moving up through the soil evaporated at the surface. Chapter 3 9

Kinds of Soil Horizons

soil horizon is a layer of soil paral- Gradual changes from one master hori- lel to the earth’s surface. It has a zon to another give rise to transition A unique set of physical, chemical, horizons. These are named with two and biological properties. The properties letters, for example, AB, BA, BC. Special of soil horizons are the results of soil- kinds of master horizons are named by forming processes, and they distinguish adding lower case letters—for example Ap, each horizon from other horizons above Bt, Cr. Thick horizons may be subdivided and below. using Arabic numbers, as in Al, A2, or Bw1, Soil horizons are named using combina- Bw2, Bw3. tions of letters and numbers. Six general A single soil profile never has all the kinds of horizons may occur in soil pro- horizons that are possible. Most Oregon files (Figure 5), and they are named with soils have A, B, C, and one or two transi- capital letters: O, A, E, B, C, R. These are tion horizons. Other Oregon soils may called master horizons. have an A horizon resting directly on a C horizon, or an A-E-B-C horizon sequence, or even an O-E-B-C sequence. Litter layer Because all six master horizons occur somewhere in Oregon, we need to know Mineral surface horizon, dark- what each one is and how it differs from colored, granular structure the others.

Strongly leached horizon, Master Horizons light-colored, platy structure Each master horizon has a distinct set of properties. Subsoil horizon of maximum development, “brown,” blocky O horizon structure The O stands for organic. O horizons don’t have to be 100 percent organic Weathered “parent material,” material, but most are nearly so. Forest “brown,” massive structure soils usually have thin organic horizons at the surface. They consist of leaves and twigs in various stages of decay (Plate 1). Wet soils in bogs or drained swamps often have O horizons of or muck. Hard bedrock Soils in Lake Labish, Waldo Lake, and Lower Klamath Lake all have O horizons of this kind. Other than these, very few agricultural or rangeland soils in Oregon have O horizons. Figure 5.—Generalized soil profile. Each master horizon is shown in the relative position in which it occurs in a soil profile. All six master horizons are shown, even though any one soil usually has only three or four. 10 Chapter 3 • Kinds of Soil Horizons

A horizon horizon, and you may be able to see clay skins (Plates 3, 5, 6, and 9). Each of these The A horizon is the surface horizon of major kinds of B horizons is discussed mineral soil. Its unique characteristic is a more fully in the next section, “Special dark color formed by addition of humus Kinds of A, B, and C Horizons.” (Plates 3, 4, 5, 6, 8, and 12). Granular or fine blocky structure (aggregate shape) C horizon and friable consistence (ease of crushing) also are typical. The C horizon is weathered geologic The thickness of A horizons ranges material below the A or B horizon. Any- from a few inches in dry, rangeland soils thing that you can dig with a spade but to over 20 inches (50 cm) in some which has not been changed very much Willamette Valley soils. Every cultivated by soil-forming processes is considered agricultural soil has an A horizon. C horizon (Plates 1, 2, 3, 4, 9, and 13). A horizons are extremely important in maintaining and providing a R horizon favorable environment for root growth. R stands for rock. It refers to hard They should be protected from damage by bedrock that you can’t easily dig with a erosion or compaction. spade. Depending on the depth to bed- E horizon rock, the R horizon may occur directly beneath any of the other master horizons This horizon has a light gray or white (Plate 12). color. It’s not present in all Oregon soils, To judge an R horizon, mark its color, but when it is, it usually occurs immedi- and check none for mottles and NA for ately beneath an O or an A horizon texture. Bedrock essentially is 100 percent (Plates 1, 5, 6, and 11). coarse fragments, so check more than E horizons are light-colored because 60 percent. The structure type is massive nearly all the iron and organic matter has and the grade is structureless. been removed. You can think of the E as meaning exit or leaching. Special Kinds E horizons occur in several of the sandy soils along the Oregon coast. They also of A, B, and C Horizons occur in some wet, silty soils that have Many horizons are the result of unique dense, clayey . In the wet soils, processes that leave a distinct mark on the E horizon also has noticeably less clay the horizon. We identify these horizons than the B horizon beneath it. with a lower-case letter immediately following the master horizon symbol. B horizon Over 25 letters and combinations of The B horizon is the subsoil layer that letters are possible. We’ll discuss only changes the most because of soil-forming nine that you are most likely to encounter processes. Several kinds of changes are in Oregon soils. possible. In some soils, the B horizon has the Ap horizon brightest yellowish-brown or reddish- The surface horizon of any soil that has brown color (Plates 1, 2, 4, 5, 9, and 12). In been plowed or cultivated is called the others, it has the most evident blocky or plow layer (Plates 2, 6, 9, and 12). That’s prismatic structure (Plates 2 and 3). Many what the p stands for. Cultivation thor- B horizons have more clay than any other oughly mixes the upper 8 to 12 inches Special Kinds of A, B, and C Horizons 11

(20 to 30 cm) of the soil and destroys any Bs horizon natural horizons that may have been present. We call this horizon a spodic horizon. If the original A was very thick, plowing It’s common only in some of the sandy converts the upper part into an Ap, and soils on marine terraces along the Oregon the lower part remains simply as a second coast. A few soils at very high elevations A horizon. If the original A was very thin, in the Cascades and the Blue Mountains then the Ap could rest on a B, a C, or a also have spodic horizons. transition horizon. The color of a spodic horizon is quite Even when a soil has been severely distinctive. It’s usually bright yellowish- eroded, such that all the original A is gone, brown or reddish-brown, and it fades with plowing an exposed B or C horizon would depth (Plate 1). Often there’s a thin black automatically make the surface horizon an Ap. layer at the top. The spodic horizon forms when iron, aluminum, and organic matter Bt horizon all are leached out of surface horizons, carried downward, and deposited in the The t stands for texture. Textural B subsoil. horizons have distinctly more clay in them than the horizons above or below. Bw horizon You can feel the difference. Some of the clay comes from the soil Think of the w as meaning weathered. above the Bt. Water moving down through Bw horizons have been changed by weath- the soil carries very fine clay particles ering, but not enough to form a Bt, Bg, or with it. When the downward movement Bs. In Oregon soils, the Bw differs from the stops, the clays are deposited, building up C by having weak or moderate blocky the waxy coatings we call clay skins. Some structure (see page 25). The Bw also may of the clay also comes from the weather- have a little brighter color (Plates 2, 4, 11, ing of original minerals in the Bt. and 12), and it may be more leached than Bt horizons are quite common in the C. Oregon soils. They usually have well- Bw horizons are common in soils of the developed blocky or prismatic structure Cascade and Coast Range Mountains, in (Plates 3, 5, 6, and 9). young soils on river floodplains and low terraces, and in many soils of eastern Bg horizon Oregon. This horizon is gleyed. That means it’s Bx horizon very wet for long periods of time. Iron in the soil is chemically reduced, and much This refers to a special feature called a of it has been leached out of the soil. As a . It is a massive, dense, but not result, gleyed horizons usually are dark cemented, soil horizon. The fragipan is gray in color (Plates 7 and 8). They also often mottled and has streaks of gray may be mottled (see page 17), but not scattered throughout (Plate 11). The necessarily so. fragipan is so dense that neither plant Gleyed horizons almost always tell us roots nor water can penetrate, except in that the soil is poorly or very poorly the gray silt streaks. In Oregon, drained. Gleying is not restricted to the occur only in some of the upland soils of Bg; other gleyed horizons include Ag, BAg, Columbia, Washington, Multnomah, and BCg, Cg. Clackamas counties. 12 Chapter 3 • Kinds of Soil Horizons

Bk horizon Cr horizon This horizon has an accumulation of Weathered bedrock, or rock that is soft calcium carbonate, or free lime. Carbon- enough to slice with a knife or a spade, is ates leached from upper horizons have called Cr (Plate 13). It’s rock material, and been redeposited in the Bk (Plate 9). You you often can see original rock structure, should be able to see white streaks or but it’s not hard enough to be desig- nodules of lime. These will bubble vio- nated R. lently when a drop of hydrochloric acid When judging a Cr, first record its color, (HCl) is placed on them. then check none for mottles, NA for Be careful though. Some soils in eastern texture, and more than 60 percent coarse Oregon have had free lime in them right fragments. The structure type is massive from the beginning. They will react to the and the grade is structureless. acid, too. We use the k only to indicate a horizon enriched in carbonates by trans- Transition Horizons location. A Bk horizon may very well have an ordinary C horizon beneath it that Master horizons rarely change abruptly contains only its original amount of lime. from one to another. Instead, the changes occur gradually throughout a zone that Bkqm horizon may be 5 or 10 inches thick. These zones are called transition horizons. There are This horizon is called a duripan three common ones in Oregon soils. (Plate 10). It is enriched with calcium carbonate (k) and silica (q), and it is AB horizon strongly cemented (m). Duripans are common in several soils of This transition horizon occurs between eastern Oregon. Limited rainfall has the A and the B. It’s dominated by proper- leached lime and silica from the upper 10 ties of the A, but some of the properties of to 20 inches of soil and redeposited them the B are evident. Dark colors associated in the Bkqm. Thin, pinkish coatings of with organic matter are fading because opal may be present on the upper sur- organic matter is decreasing (Plate 4). The faces of duripan fragments. The duripan structure often changes from granular to usually is only 6 to 10 inches thick, but it is subangular blocky (see Chapter 4, “Soil so cemented that plant roots can’t go Structure”). through it. A dense mat of roots spreading horizon- BA horizon tally is a good indicator of a duripan. This horizon also occurs between the A Sometimes, however, there are fractures and the B, but it has more of the charac- in the duripan that will allow some plant teristics of the B. Generally, the structure roots to find a way down. And if the pan is will be the same type as the B, but less only weakly cemented, you can break it strongly expressed. The color may be a up even more by ripping. little darker than the B (Plate 3), or the For soil judging contests, mark the most clay content may be less than the maxi- appropriate color. Check none for mot- mum in the B. tling, NA for texture, and more than 60 percent coarse fragments. The struc- BC horizon ture type is massive and the grade is struc- tureless. This is a transition from B to C. Proper- ties of the B are dominant, but some influence of the C horizon is evident Subdivisions of Thick Horizons 13

(Plates 2 and 3). Often the clay content If soil horizons are developed in more will be less than the maximum in the B, than one material, we place a number in but more than in the C. Or the color will front of the horizon name to indicate its be fading. If the C is massive, the BC has position from the top down. structure, but it may have larger units and The geologic material at the surface is be more weakly expressed than in the B. always assumed to be the first one, and the number 1 is never used. Subdivisions The second geologic material is indi- cated by a 2, the third by a 3, and so on. of Thick Horizons Thus a soil developed in silt over Sometimes one or two of the horizons could have the following set of in a soil are so thick that they need to be horizons: A-AB-B-2BC-2C. subdivided. Small changes in texture, color, or structure commonly are used to make the subdivision. Subdivisions, or vertical sequences within any single kind of horizon, always are indicated by a number immediately following the letter symbol(s). Here are a few examples of some thick soil horizons that could be subdivided: Thick A horizon—Al, A2 (Plate 8) Thick Bg horizon—Bg1, Bg2 (Plate 7) Thick Bt horizon—Bt1, Bt2 (Plate 5) Thick Bw horizon—Bw1, Bw2 (Plate 2) Thick C horizon—C1, C2 (Plates 3 and 4) More Than One Kind of Parent Material Parent material is the geologic stuff from which soils form. It may be a river deposit, volcanic ash, clays weathered from rock in place, or one of many other kinds of materials. When all the horizons of a soil have formed in a single kind of parent material, we simply use the ordi- nary A, B, and C designations. Some soils, however, have formed in more that one kind of parent material. A Figure 6.—Multiple parent materials. The gray material is flooding river, for example, may deposit recent volcanic ash resting on older, more weathered soil fresh silts on top of older and material. Notice the abrupt contact between the two contrast- gravels. Or volcanic ash may be deposited ing materials. on top of weathered bedrock. 14 Chapter 3 • Kinds of Soil Horizons

Typical Horizon Sequences 1. Look for color changes. Where there is an obvious color change there also is a Several common Oregon soils are listed horizon change. Color alone, however, is below, followed by the names of the not sufficient to separate all horizons. horizons in a typical profile. Nearly all Several soils in Oregon have nearly geographic areas of Oregon are repre- uniform colors extending all the way sented by the soils on this list. through the B and into the C. Alicel Ap-A-BA-Bw-2C 2. Take a knife and gently poke the soil Bandon O-E-Bs1-Bs2-Bs3-Bs4-C every few inches from the surface down Brenner Ap-A-Bg1-Bg2-BCg-Cg to the lower part of the pit. Often you Carney A1-A2-AB-C-2R can “feel” the firmer consistence of Cascade A-Bw1-Bw2-2Bx1-2Bx2-2Bx3 subsoils and restrictive layers. You may Dayton Ap-E-2Bt-2BCt-3C even be able to locate a contact Deschutes A-BA-Bw-2C-3R between B and C this way. Fordney Ap-C1-C2 3. Starting at the top, check the soil tex- Gem Al-A2-BAt-Bt1-Bt2-BCt-BCtk-R ture with your fingers every 2 to Hoopal A1-A2-Bw-Bkqm-C 4 inches. If there is a marked increase in Josephine O-A-BA-Bt1-Bt2-Bt3-C-Cr clay from A to B, you should detect it Malabon Ap-AB-Bt1-Bt2-BCt-2C this way. A decrease in clay from B to C Nehalem Ap-A-Bw-C also should be evident. Nyssa Ap-Bw-Bkq-Bkqm1-Bkqm2 4. With your knife, remove a handful of soil Oakland A1-A2-Bt1-Bt2-Bt3-BCt-Cr from the upper 4 inches of soil. Carefully Quincy C1-C2 break it apart and observe the size, Ritzville Ap-BA-Bw-Bk-C1-C2 shape, and strength of structural aggre- Salem Ap-Bt-BCt-2C gates. Repeat this process every 4 to Simas A-2Bt1-2Bt2-2BCk1-2BCk2 6 inches down through the profile. Walla Walla Ap-A-BA-Bw-BCk1-BCk2 Structural changes may be a good clue to boundaries between horizons and to the presence of transition horizons. Locating Boundaries 5. Each time you locate a tentative bound- Between Horizons ary, mark it with a nail, twig, or some other convenient marker. As you con- The most useful thing you can do to sider more and more characteristics, help yourself find and name soil horizons you may want to adjust some of the is to prepare a good exposure of the soil boundaries up or down. profile. Either a good pit or a road cut will 6. When you have settled on an initial set do, but in either case you should clean up of horizon boundaries, start looking the face of the vertical cut. Use your knife more carefully at the color, texture, to pick off any soil that may have fallen structure, pores, clay skins, etc. of each down from the surface or that was horizon. With a complete set of informa- smeared by a shovel or a backhoe. After tion, you may wish to make a final you have a good, fresh surface, try each of adjustment in your horizon boundaries. the following techniques.