- -  AGRICULTURE CORE CURRICULUM - -


(CLF6000) Advanced Core Cluster: ORNAMENTAL HORTICULTURE

 (CLF6350)  Unit Title: ELEMENTS NECESSARY FOR PLANT GROWTH

____________________________________________________________________________
 (CLF6356)  Topic: USES OF FERTILIZERS    Time     Taught in Year(s) 
                                             1 hour         3 AND 4    
____________________________________________________________________________

        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: WESTERN FERTILIZER HANDBOOK (7th ed.). (1985). 
                      Danville, IL: Interstate Printers and Publishers.

        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 most important benefits of soil organic matter are that they: 

   1. Help build stable aggregates, thus improving soil texture and tilth. 

   2. Improve water penetration and soil aeration. 

   3. Improve moisture holding capacity. 

   4. Provide a source of many plant nutrients. 

   5. Swell and shrink and absorb nutrient salts. 

   6. Act 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 above list of the 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
           more mineral nutrients are made available.

       b) Negatively in that they compete directly with plants for 
           nutrients that are available; they are present almost everywhere 
           in the soil whereas plant roots are not.

   3. They 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 of inorganic fertilizers are needed because they are 
       much more concentrated. This helps keep down the cost and also 
       speeds 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 
       air to the soil.

   5. Nitrogen fixation, then, is changing the free nitrogen (N2) to a
       form usable by plants (nitrogen compounds, mostly amines such as
       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.


1/6/91 PJK/clh


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