- -  AGRICULTURE CORE CURRICULUM - -


(CLF6000) Advanced Core Cluster: ORNAMENTAL HORTICULTURE

 (CLF6350)  Unit Title: ELEMENTS NECESSARY FOR PLANT GROWTH

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 (CLF6351)  Topic: PRIMARY, SECONDARY,      Time     Taught in Year(s) 
                     AND MICRONUTRIENTS       1 hour       3 and 4      
                     NECESSARY FOR PLANT                                      
                     GROWTH
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        Topic Objectives: Upon completion of this lesson the student will 
        be able to:

        Learning Outcome #:

          (H-1) - List the primary, secondary, and micronutrient 
                    elements necessary for plant growth.

        Special Materials and Equipment: None

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

        Evaluation: Quiz by instructor

TOPIC PRESENTATION: PRIMARY, SECONDARY, AND MICRONUTRIENTS NECESSARY FOR 
                    PLANT GROWTH

A. There are more than 100 elements known today.

   1. Although more than 90 elements can be absorbed by plants, only 16 of 
       these have been shown to be essential for plant growth. (Scientists 
       have recently discovered that nickel may also be an essential
       element for plant growth.)

B. The primary plant nutrients and their chemical symbols are: 

              Nutrient                   Chemical Symbol

              nitrogen                        N
              phosphorus                      P
              potassium                       K

   1. Nitrogen is taken into plants primarily as nitrate (NO3-) or
       ammonium (NH4+) ions.

       a. Plants can utilize both of these forms of nitrogen in their 
           growth processes.

       b. Most nitrogen is taken up in the nitrate form (primarily because 
           bacteria or microbial activity in soil converts NH4 + 0 to 
           NO3- very rapidly).

       c. Nitrogen is most often the limiting nutrient in plant growth.
           It is utilized by plants to synthesize amino acids which then
           form proteins and it is a constituent of chlorophyll.

       d. The protoplasm of all living cells contain protein.

       e. Microbial activity in the organic matter of soil makes nitrogen 
           available to plants.

       f. This microbial process is slow and therefore produces only about 
           20 to 60 pounds of nitrogen per acre each year.

       g. Nitrogen is the most limiting nutrient for most crops grown in 
           California, the U.S., and the world.

   2. Depending on the soil pH, phosphorus (P) is absorbed by the plants 
       as H2PO4- (dihydrogen phosphate) or HPO4= (monohydrogen phosphate).

       a. Most phosphorus is tied up in the soil in compounds of limited 
           solubility.

       b. That phosphorus available to the plants may be as little as 1 
           percent or less of the total amount present in the soil.

       c. Phosphorus is present in all living cells being used by plants 
           to form nucleic acids (DNA and RNA).

       d. It stimulates early growth and root formation, hastens maturity, 
           and promotes seed production.

   3. Potassium (K) is taken up by plants in the form of potassium ions 
       (K+).

       a. It is responsible for translocation of sugars and starch 
           formation.

       b. It serves as a catalyst (like grease makes wheels turn or move 
           more easily) in many biochemical reactions.

       c. It is required in the opening and closing of the stomata by 
           the guard cells. 

       d. It increases size and is essential for high quality forage 
           crops.

C. Listed next are the secondary plant nutrients. These are needed by the 
   plants in lesser amounts than the primary nutrients but in larger 
   amounts than the micronutrients.

   1. The secondary nutrients and their chemical symbols are:

                 Nutrient               Chemical Symbol

                 calcium                     Ca      
                 magnesium                   Mg
                 sulfur                      S

   2. All elements are equally essential, regardless of the amounts 
       required.

D. The micronutrients are needed in the least amounts. They include:

                Nutrient                Chemical Symbol

                zinc                         Zn
                iron                         Fe
                manganese                    Mn
                copper                       Cu
                boron                        B
                molybdenum                   Mo
                chlorine                     Cl
                (perhaps nickel)             Ni

E. To complete the 16 essential elements we include carbon (C), hydrogen 
   (H), and oxygen (O).

   1. These three are not mineral nutrients, but they are essential 
       elements.

   2. Carbon forms the skeleton of all organic molecules. It is a basic 
       building block for plant life.

       a. Carbon is taken from the air by plants in the form of carbon 
           dioxide (CO2).

       b. Through photosynthesis it is combined with hydrogen and oxygen 
           from water to form carbohydrates.

   3. Oxygen is required for respiration in plant cells.

   4. Hydrogen combined with oxygen forms water, which makes up a large 
       proportion of the total plant weight.

   5. These three elements--carbon, hydrogen and oxygen--are supplied to 
       plants primarily from air and water.



1/6/91 PJK/clh


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