Manual for Juding Oregon Soils
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Manual 6 • Reprinted September 2007 $12.50 MANUAL FOR JUDGING OREGON SOILS MANUAL FOR JUDGINJUDGINGG OREGON SOILS OREGON STATE UNIVERSITY EXTENSION SER OREGON STATE VICE Contents i Chapter l Why Study Soil? ............................................................................................... 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 Soil Structure ..................................................................... 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 Erosion 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 Erosion Control 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 soil Conservation 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 soil management 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 root 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