- -   AGRICULTURE CORE CURRICULUM  - -


(CLF7000)  Advanced Core Cluster:  PLANT AND SOIL SCIENCE

  (CLF7450)   Unit Title:  ELEMENTS NECESSARY FOR PLANT GROWTH

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  (CLF7452)   Topic:  SOURCES OF NITROGEN          Time    Taught in Year(s) 
                      PHOSPHORUS AND POTASSIUM    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-2)  -  List a source of each of the primary elements:  N, P, 
                     and K.

         Special Materials and Equipment: None

         References: Interstate Printers and Publishers, Inc.,
                     WESTERN FERTILIZER HANDBOOK.  Pages 84 to 101.

                     Hartman, H., et.al.  PLANT SCIENCE. Pages 206 to 210.

         Evaluation: Quiz by instructor

TOPIC PRESENTATION:  SOURCES OF N, P, K

A.  The earliest of fertilizer materials were animal manures, plant and 
    animal residues, ground bones, and wood ashes.

    1.  To maintain or improve the original soil fertility, nutrients must 
        be added in one form or another in amounts equal to or greater than 
        those removed by the crop.

    2.  Today the necessary elements added to our soil or crops as 
        fertilizers come from a variety of sources.

B.  Nitrogen (N) is available in several forms from several different 
    sources.

    1.  Large amounts of nitrogen (300-1000 pounds of nitrogen per acre per 
        year) are "fixed" by legumes like alfalfa and the clovers through
        the symbiotic association with the bacteria in the nodules on the
        roots which take nitrogen gas from the air and covert it into amino
        acids and proteins.

    2.  Ammonium nitrate is a common form (compound) of nitrogen used. 

        a.  It is manufactured by reacting nitric acid HNO3 with anhydrous 
            ammonia NH3.

        b.  The reacted material is concentrated and either prilled or 
            granulated.

        c.  It is normally coated to prevent caking. 

        d.  The commercial product contains 33.5 to 34 percent nitrogen.

    3.  Ammonium sulfate (NH4)2 SO4 is widely used as a fertilizer. 

        a.  It contains 24 percent sulfur and 21 percent nitrogen. 

        b.  It is manufactured by reacting anhydrous ammonia with sulfuric 
            acid. 

        c.  The final product is in a crystalized dry form.

    4.  Urea is also a widely used nitrogen fertilizer. 

        a.  Ammonia and carbon dioxide are reacted together to form urea. 

        b.  The fertilizer grade of dry urea contains about 46 percent 
            nitrogen.

    5.  There are several other forms of nitrogen fertilizers available, 
        each with their own advantages.

C.  Phosphate rock (apatite) deposits are the basic source of all phosphate 
    (P) fertilizer materials. 

    1.  Apatite exists in several forms, all of which are more or less 
        insoluble in water. 

    2.  To increase phosphorus availability to plants, apatite is treated 
        with heat and acids when made into fertilizer.  There 
        are several commercially available forms of phosphorus.

    3.  Rock phosphate treated with sulfuric acid yields superphosphate.
        This is the most abundant phosphorus source containing 16 to 20 
        percent phosphoric acid (P2O5).

    4.  Liquid phosphoric acid (H3PO4) is also made by treating apatite with 
        sulfuric acid (a wet process).  It contains 40 to 50 percent P2O5.

    5.  Triple superphosphate uses a similar process by reacting phosphoric 
        acid with rock phosphate and ends with a dry granular product 
        containing 44 percent phosphate.  (Note P205 x .44=P)

D.  Potassium (K) is found throughout the world in both soluble and 
    insoluble forms.

    1.  The U.S. has large deposits in New Mexico, Oklahoma, and Texas.

    2.  The most widely used potassium fertilizers are potassium chloride 
        (muriate of potash), potassium sulfate, and potassium nitrate.

        a.  Potassium chloride (KCl) is 50 percent K (60% K2O).

        b.  Potassium sulfate (K2SO4) is 42 percent K (50% K2O).

        c.  Potassium nitrate (KNO3) is 37 percent K (44% K2O)
            plus 13% total nitrogen.

        Note:  K20 x .83 = K

    3.  Potassium chloride must be used with caution on some soils.
        Its chloride content can contribute to chloride toxicity which may
        injure or kill plants.

6/21/90  sg


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