- -   AGRICULTURE CORE CURRICULUM  - -


(CLF7000)  Advanced Core Cluster:  PLANT AND SOIL SCIENCE

  (CLF7450)   Unit Title:  ELEMENTS NECESSARY FOR PLANT GROWTH

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  (CLF7456)   Topic:  USES OF FERTILIZERS     Time      Taught in Year(s) 
                                             1 hour          3 AND 4     
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         Topic Objectives:  Upon completion of this lesson the student will 
         be able to:

         Learning Outcome #:

           (H-10) -  List three advantages of organic and three advantages 
                     of inorganic fertilizer.

           (H-8)  -  Discuss the process of nitrogen fixation and identify 
                     plants with this ability.

         Special Materials and Equipment: None

         References: Interstate Printers and Publishers, Inc.
                     WESTERN FERTILIZER HANDBOOK,.
                     Pages 139-147.

         Evaluation: Quiz by instructor

TOPIC PRESENTATION:  USES OF FERTILIZERS

A.  Fertilizers have probably increased crop yields more than any other 
    single agricultural practice.

    1.  Mineral nutrients are supplied to the soil by applying crop 
        residues, animal manures, synthetic chemical fertilizers, or natural 
        minerals. 

    2.  Some nutrients enter the soil from the atmosphere, irrigation water,
        rainfall and from the elemental nutrients of the soil itself. 

    3.  The actual source of the nutrient, whether organic or inorganic, is 
        unimportant to the plant so long as the mineral nutrients are 
        available in adequate amounts and can be easily assimilated (taken
        chemically into the plant).

B.  Organic matter content of the soil has an extraordinary effect on its 
    biological, chemical and physical properties. 

C.  Crop residues, green manure crops, animal manures and other organic 
    matter can be incorporated into the soil to gain specific advantages.

D.  The principle benefits of soil organic matter are that it: 

    1.  Helps build stable aggregates, thus improves soil texture and tilth. 

    2.  Improves water penetration and soil aeration. 

    3.  Improves moisture holding capacity. 

    4.  Provides a source of many plant nutrients. 

    5.  Swells and shrinks and absorbs nutrient salts. 

    6.  Acts as a storehouse of nutrient bases.

E.  There are some advantages of using organic materials over the use of 
    inorganic fertilizer.

    1.  They help to amend soil.  (See the list shown above, benefits of 
        organic matter.)

    2.  They increase the activity of microorganisms.  (These affect both 
        positively and negatively the availability of mineral nutrients 
        in soils.)

        a)  Positively in that with greater activity of microorganisms their 
            decomposing bodies represent a somewhat larger (hopefully) pool 
            of "available" nutrients. 

        b)  Negatively in that they compete directly with plants for 
            nutrients that are available but are at a positional advantage 
            because they are present almost everywhere throughout the soil.  
            Whereas plant roots are not.

    3.  Provide a continuous supply of nutrients over a long period of time. 
        This is usually a disadvantage for short growing season crops.

F.  Some advantages are gained, however, from the use of inorganic 
    fertilizers.

    1.  Inorganic fertilizers are usually less expensive than organic 
        materials. 

    2.  They are easier to apply.  These commercial materials can be 
        manufactured into many convenient forms (crystals, prills, granules,
        powders). 

    3.  Lesser amounts are needed because they are much more concentrated. 
        This helps keep down the cost and speed of application. 

    4.  Inorganic fertilizers are readily available for plants and can be 
        applied to correspond with the period of greatest plant need.  Thus, 
        providing for greater efficiency of uptake.


G.  Some microorganisms have the ability to increase the nitrogen content of 
    our soils. 

    1.  We call this "nitrogen fixation". 

    2.  Nitrogen in its elemental form (N2) is a colorless inert gas.

    3.  The atmosphere contains approximately 79 percent nitrogen.  (In the 
        N2 form).

    4.  Two groups of bacteria have the ability to "fix" nitrogen from the 
        soil air. 

    5.  Nitrogen fixation, then is changing the free Nitrogen (N2) to a form 
        useable by plants. (Nitrogen compounds, mostly amines - NH2.)

    6.  The two groups of bacteria that accomplish this fixing are symbiotic 
        and nonsymbiotic. 

    7.  The most important group of these bacteria are those that cause the 
        formation of nodules on the roots of legumes. 

        a.  These organisms derive their food and minerals from the legume, 
            and in turn they supply the legume with some or all of its 
            nitrogen. 

        b.  This growing together for a mutual benefit is called "symbiosis" 
            and so these bacteria are called symbiotic nitrogen-fixing 
            bacteria. 

        c.  These bacteria are from the genus, Rhizobium. 

        d.  There are specific species of this type of bacteria for each 
            group of legumes.  All of these crops are involved in nitrogen 
            fixation.

            1)  alfalfa 

            2)  clover

            3)  cowpea

            4)  vetch

            5)  soybean

            6)  bean

            7)  lupine


    8.  The nonsymbiotic bacteria that fix nitrogen live in the soil 
        independently. 

        a.  Two common genera of bacteria involved here are the Azotobacter 
            and Clostridium. 

        b.  Compared to the symbiotic bacteria, these are considerably less 
            important.


7/25/90 sg


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