- -   AGRICULTURE CORE CURRICULUM  - -


(CLF7000)  Advanced Core Cluster:  PLANT AND SOIL SCIENCE

  (CLF7500)   Unit Title:  SOIL TILLAGE, LAND PREPARATION AND CONSERVATION

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  (CLF7504)   Topic:  ROOT INTERACTION           Time      Taught in Year(s) 
                      WITH THE SOIL             1 hour         3 and 4    
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         Topic Objectives:  Upon completion of this lesson the student will 
         be able to:

         Learning Outcome #:

           (I-8)  -  Explain how roots interact with the soil.

         Special Materials and Equipment: None

         Evaluation: Quiz by instructor

TOPIC PRESENTATION:  ROOTS INTERACTION WITH THE SOIL

A.  Roots are the first organ to emerge from a germinating seed. 

    1.  Root systems are of two types, tap or fibrous. 

    2.  Root systems may be deep or shallow, sparse or dense, 
        depending on plant species and environment.

    3.  The main functions of roots are absorption, anchorage 
        and storage.

    4.  There are other functions and affects of roots that are 
        often overlooked. 

B.  Environmental factors influence the direction and extent of root growth.

    1.  Light, gravity, temperature, salt concentration, soil texture, 
        oxygen supply, moisture and mineral nutrient supply can all
        affect root growth.

    2.  A granular soil structure is probably the most ideal for 
        establishing crops from seed or small plants. 

        a.  The larger pores between aggregates are continuous 
            so roots can explore the soil thoroughly. 

        b.  Water drains well from this soil, yet moisture is 
            held in the aggregates. 

        c.  Roots need to have air as well as water and minerals
            and need it continuously to maintain healthy plants. 

C.  Plant roots grow and die in the soil. 

    1.  Roots in most plants are between 30 to 50 percent of the total plant
        mass. 

        a.  The root system will be in balance with the top and
            be able to supply what is needed. 

        b.  The weight and physical size of the root system 
            need not be equal to the above ground portions of 
            the plant. 

    2.  Dead roots, sloughed materials and exudates influence microbial 
        activity. 

        a.  Exudates include such organic compounds as alkaloids,
            vitamins, nucleotides, flavones, sugars, enzymes,
            auxins and amino acids. 

        b.  Most of these have a positive effect on microbial 
            activity but a few may have a negative effect. 

    3.  Living roots physically modify the soils as they push through cracks 
        and make new openings of their own. 

        a.  Tiny initial channels are increased in size as roots
            swell and grow. 

        b.  As roots die and decompose they provide building
            materials called humus in the soil.

4.  Roots help to reduce erosion. 

    a.  Roots of all plants, but especially grasses help hold
        soil together and prevent it from washing away. 

    b.  Man has made use of this technique in our conservation
        programs in planting grass waterways and in contour
        strip cropping. 

5.  As plants die, their roots decompose in place, leaving channels in the 
    soil.

    a.  These openings help in increasing soil aeration.

    b.  Both water penetration and the rate of water movement 
        is increased by these root channels. 

    c.  It has been suggested by some researchers that cover crops 
        (green manure crops) will give the best results when 
        they are chopped at ground level rather then disced into
        the soil. 


        1)  In this way the root channels that form as the roots
            decay will leave a continuous passage for water and 
            air from soil surface in the subsoil areas. 

        2)  The above ground portion of the crop becomes a mulch.

6/21/90 sg

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