- -   AGRICULTURE CORE CURRICULUM  - -


(CLF7000)  Advanced Core Cluster:  PLANT AND SOIL SCIENCE

  (CLF7550)   Unit Title:  MANAGEMENT PRACTICES NECESSARY FOR IRRIGATION 
                           AND DRAINAGE

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  (CLF7553)   Topic:  IRRIGATION MEASUREMENTS    Time      Taught in Year(s) 
                      AND COSTS                 4 hours         3 and 4    
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         Topic Objectives:  Upon completion of this lesson the student will 
         be able to:

         Learning Outcome #:

           (J-8)  -  Given the appropriate information, calculate the 
                     appropriate amount of water needed and the cost for 
                     that water for a complete production cycle of a major 
                     local crop.

           (J-8)  -  Determine the acre feet of water needed to irrigate a 
                     local crop.

           (J-9)  -  Describe how and why salts (e.g. selenium and nitrate 
                     ions) can become a problem in agricultural waste water 
                     run-off.

         Special Materials and Equipment: Sample problems for determining 
                     water costs and for measuring water quantity.

         References: University of California.  RESOURCES AT RISK.
                     Curriculum Development Project.  LESSON PLANS FOR THE 
                       BASIC CORE CURRICULUM
                     Donahue, Roy L.  SOILS.  
                     American Society of Agronomy.  CROPPING STRATEGIES FOR 
                       EFFICIENT USE OF WATER AND NITROGEN.  Pages 167-189.

         Evaluation: Quiz by instructor

TOPIC PRESENTATION:  IRRIGATION MEASUREMENTS AND COSTS

A.  The amount of water that must be added by irrigation will vary with the 
    soil, climate, type of crop, and the length of time to maturity.

    1.  The object of irrigation is to replace water lost from the crop's 
        root zone by transpiration and evaporation minus the annual
        rainfall. 

    2.  Irrigation principles are simple.


    3.  However, hard and fast rules are difficult, because the needs of 
        different crops in different area vary so greatly. 

B.  Generally soil should not be allowed to reach permanent wilting percent 
    before adding more water.

    1.  Experience indicates that with each irrigation, depth of water 
        penetration is a little less. 

    2.  Dry soils do not wet as easily as soils with some moisture.

    3.  Water moves through a soil only at Field Capacity (F.C.); it must 
        thoroughly wet a soil before it can go deeper. 

    4.  You cannot partially wet a soil; a small irrigation goes down a 
        short distance. 

    5.  Depth of water penetration can be determined by the use of 
        tensiometers or by using a soil auger or soil-sampling tube.

C.  The quantity of water added at each irrigation varies according to the 
    soil moisture content, depth, and water holding capacity of the soil. 

    1.  The depth of penetration will vary with the soil and will often vary 
        throughout the field.

    2.  Some soils will hold less than 1 inch of water per foot (depth) of 
        soil; others will hold more than 2 inches. 

D.  Cost of irrigation water will vary with the irrigation district and/or 
    the type of fuel used to pump the water, and the depth from which water 
    is pumped from underground sources.

    1.  In some areas water cost is a major factor in determining a crops 
        profitability.

    2.  Sometimes only high-valued specialty crops can be grown profitably 
        when water costs are high (e.g., avocado, strawberries).

E.  See the Water Measurements, in the LESSON PLANS FOR THE BASIC CORE 
    CURRICULUM (CLF354) for examples of calculating the amount of water 
    needed and the cost of water.

F.  Nearly all nitrogen fertilizers are soluble in water and the nitrates 
    move readily in the water.  (Exceptions are organic and other slow-
    release fertilizers.)

    1.  Nitrogen can be washed by surface flow of rain or irrigation waters 
        into drainage waters.

    2.  Water can also carry nitrates deep into the soil, especially in 
        sandy soils. 

    3.  There is a human health concern on the issue of nitrates in drinking 
        water.  In some areas it is possible that they have seeped into 
        groundwater in large enough quantities to be harmful to the health 
        of people or livestock that drinks that water. 

    4.  Some important factors that influence the amount of nitrate movement 
        to groundwater or surface waters are: 

        a.  The amount of nitrate dissolved in the soil solution, 

        b.  the rate of its use by plants,

        c.  the amount of water available for runoff and leaching the soil,
            and 

        d.  soil permeability. 

G.  Selenium can also be found in areas of agricultural drainage. 

    1.  Selenium is a nonessential mineral that is absorbed by plants when 
        it is present in the soil on which they grow.  It can be toxic to 
        plants if too much is absorbed. 

    2.  In trace amounts, selenium is essential to animal life, but in 
        higher concentration it is very toxic to animals.

    3.  A nutritional disease commonly called "alkali disease" is the result 
        of selenium poisoning of livestock. 

    4.  Wheat grown in areas where the soil is high in selenium poses a 
        potential threat to human health. 

    5.  Too much selenium, like too much salinity, retards plant growth. 

    6.  Levels of selenium in some farmland areas of western San Joaquin
        Valley are high enough to justify careful monitoring.

          __________________________________________________________
          ACTIVITY:  
                      
          1.  Have students determine water costs and how to
              measure acre feet.  See (CLF354 BASIC CORE LESSON) 
              for reference.
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7/25/90 sg


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