Answer guide for homework 1 2002


The value of the homework is ten points.  Each correct definition is worth 0.3 points, (19*0.3=5.7 points), question 9 is worth 2.3 points and question 11 is worth two points.  There is no real “right” answer to number 11 so if they show some thinking, give them full credit.


1.  Define the terms.  Note that definitions are found in the glossary. The numbers in parentheses following the answer refers to the portion of the text where the answer can be found.


Mineral.  A mineral is (almost always) a distinct crystalline substance composed of oxygen, silicon, and aluminum.  Additional components may include iron, calcium, potassium, or magnesium. (1.2)


Colloidal.  A particle size range describing the smallest soil particles.  The size ranges from 1 nm (nanometer, 1 x 10-9 meters) to 1 mm (micrometer, 1 x 10-6 meters). (1.2, 2.1.2)


Humus.  Large, complex organic colloids formed in soils by the decay of organic matter, that are resistant to further decomposition by microorganisms. (1.2)


Soil texture.  The particle size distribution of a soil sample. (1.3)


Soil structure.  The arrangement of individual particles into a larger unit. (1.3)


Adsorption.  It is a reaction between the surface of solid particles and the charged ions and neutral molecules in the soil solution that causes the ions or molecules to become attached to the solid surfaces. (1.5)


Leaching.  The removal of ions and molecules from soils by flow of the soil solution out of the soil. (1.5)


Pedon.  A three dimensional body of soil.  A pedon typically is the minimum volume needed to enclose all of the morphological properties of a soil.  Minimum dimensions are 1 meter on a side and a depth sufficient to include all horizons. (1.1, 1.7, and Figures 1-5 and 1-6)


Profile.  A two dimensional slice of soil.  Also, the appearance of a pedon's vertical face or section. (Glossary)


Horizon.  A soil layer approximately parallel to the land surface. (1.7)


Parent material.  The initial unconsolidated or consolidated material from which a soil develops. (1.1.2)


Soil-forming factors.  Parent material, climate, relief, biota and time are the five factors that control the soil forming processes. (1.7)


Soil order.  The highest level of classification in Soil Taxonomy.  A broad grouping of similar soils. (1.9.1)


Soil series.  The most detailed level of classification in Soil Taxonomy, consisting of a central concept, a typical pedon, and a carefully defined range of properties. (1.9.2)


Soil density.  A measure of the relative amount of pores and solid particles in a soil. (1.10)


Soil survey.  The process by which information about the distribution and properties of soils is acquired. (1.10)


Soil compaction.  A process that pushes soil particles together reducing the amount and size of pores. (1.10)


Soil erosion.  The wind, water or gravity processes that remove soil from one place and transport it to another. (1.10)


Salinity.  An increased level of soluble salts that may impair plant growth. (1.10).


9.  What properties do clay and humus share that influence both soil fertility and human health?


Both have high surface area and chemical reactivity that help to retain plant nutrients that humans need and acquire by eating the plants.  The same reactivity helps to clean polluted fluids passing through soil, by sorbing metals and inactivating toxins, thus protecting drinking water.


11.      How would the world be different if there was no soil?


This is an open ended question.  No terrestrial ecosystems important to human existence would function without soils.  Without soil there would be no higher plant or animal life and even life in the sea would be limited because nutrients required for life would not be washing into the oceans from the land at the same rate from rocks as from soils.