- -   AGRICULTURE CORE CURRICULUM  - -


(CLF7000)  Advanced Core Cluster:  PLANT AND SOIL SCIENCE

  (CLF7400)   Unit Title:  SOILS

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  (CLF7401)   Topic:  INTRODUCTION             Time      Taught in Year(s) 
                      TO SOILS                1 hour          3 AND 4    
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         Topic Objectives:  Upon completion of this lesson the student will 
         be able to:

         Learning Outcome #:

           (G-5)  -  List four functions the soil provides for the growing 
                     plants.

           (G-2)  -  Define soil in terms of its functions; relationship to 
                     earth, economic uses, and components.

         Special Materials and Equipment: 

         References: Nyle C. Brady.  THE NATURE AND PROPERTIES OF SOILS.
                         10th Edition.  Pages 2 and 690 to 693.

         Evaluation: Quiz by instructor

TOPIC PRESENTATION:  INTRODUCTION TO SOILS

A.  Soil serves the functions of supplying nutrients, water, air and 
    providing anchorage for plants.

    1.  People are dependent on soils to provide them with food, fiber, 
        shelter and feed for their animals.

    2.  History reminds us to manage our soils wisely. 

    3.  Worldwide arable land is not distributed evenly with population. 

B.  Soil provides four functions for growing plants.

    1.  One of these functions is the supplying of plant nutrients.

        a.  At present, 17 chemical elements (these are discussed in a later 
            unit) are known to be essential for plant growth.  Soil is the 
            source of 15 of these.  (Note:  Ni has recently been added to 
            the list of essential elements.)


        b.  Thirteen of these 15 originate in the parent rock from which the 
            soils developed.  Nitrogen, the exception, comes basically from 
            organic matter.  N actually originates in the atmosphere and is 
            fixed by nitrogen fixation in organic matter.

        c.  Plants and soils, ultimately are derived from the parent rock, 
            but reside mostly in the organic matter in the soil.

    2.  Water is also provided by the soil. 

        a.  Water enters the plant through the roots.

        b.  Water is an essential compound in the plant as it is involved in 
            nutrient transport, enters important chemical reactions, and 
            helps to keep the plant cool.

    3.  Air and water occupy the pore spaces in the soil. 

        a.  Air replaces the space between the particles as water is 
            evaporated or transpired. 

        b.  Air supplies the oxygen which is necessary for the respiration 
            of plant roots and other living organisms in the soil.

    4.  Soil also serves as anchorage for plants.

        a.  It provides each plant with its "place in the sun".

        b.  The roots of plants comprise 30 to 50 percent of a 
            plant's total mass. 

        c.  These roots penetrate the soil and provide anchorage for the 
            plant as they absorb oxygen, water, and nutrients.

C.  People are dependent on soils; soils are dependent on people.

    1.  People can, depending on practices, keep soils as they are, improve 
        them, or let them deteriorate. 

    2.  Soils are the natural bodies on which plants grow. 

    3.  Standards of living are often determined by the quality of soils or 
        soil management and the quality of plants and animals grown on them. 

    4.  Soils also underlie the foundations of our houses and businesses. 

    5.  They serve as the bed for our roads and highways and influence the 
        quality and life of these structures. 

    6.  Soils are used to absorb our domestic wastes.

    7.  Soils and their management are of broad concern for our society.

D.  History has given us several examples of soil mismanagement. 

    1.  Mismanagement and excessive cutting of timber in specific watersheds 
        has increased erosion in some places.


    2.  Drainage systems were not maintained in the Tigris and Euphrates 
        valleys resulting in accumulation of harmful salts.  The once 
        productive soil has become barren and useless. 

    3.  The history of our own Dustbowl era is an example of not fully 
        understanding the long term significance of soils.

E.  There are more than 13 billion hectares of land on the continents of our 
    earth. 

    1.  Most of it is not suited for cultivation.  About one half of it is 
        nonarable, being mountainous, too cold, too wet, or too dry.

    2.  About one fourth of the land supports enough plant life to provide 
        grazing for animals, but cannot be cultivated. 

    3.  The remaining 25 percent of the land has the physical potential 
        for cultivation.

    a.  Only one half of this is actually under cultivation. 

    b.  The percent being cultivated varies considerably from continent to 
        continent.

        1.  In Asia and Europe almost all arable land is being used. 

        2.  In Australia and New Zealand only 12 percent of arable land is 
            cultivated. 

        3.  In North America 58 percent of our arable land is being 
            cultivated. 

    4.  Unfortunately the distribution of arable land is not related to 
        population densities.  Cultivated land per person varies from a high 
        of 0.75 hectares in North America to a low of 0.20 hectares in Asia.

7/25/90 sg 

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