AGEN 2363, Chpt. 13 notes.  Water Conservation.


I. Importance of water to agriculture and non-agriculture use:

            1. 80% + water used in U.S. devoted to agriculture

            2. Irrigated crops necessary for profits in most arable regions.

            3. Water and quality of water of national security.


II.  The Water Cycle:  know it!

    A. Surface water sources:

            - streams, ponds, lakes, reservoirs. What is the difference between a lake and a reservoir?


    B. Ground water sources:

            - Seasonal

            - ‘Perched’

            - confined aquifier,  EX  Sparta

            - unconfined aquifer,  EX alluvial

            - know what the ‘static’ water table is

            Some aquifers cover extremely large, multi-state areas.


III. Water and plants.

    A. Three types of plant water status:

            1. Sufficient.

            2. ‘Hidden’ –

            3. Visual –


    B. Four soil-water status regimes:

            1.  field capacity =

            2. permanent wilting point = -15 bar

            3. ‘available’ water =  -0.2  -  -15 bar

            4. ‘readily available’ water = -0.2  -  -1 bar


    C. Soil water holding capacities by texture:

            loams, silt loams, fine sandy loams:                2.2-2.4 in/ft

            clays                                                                2.0-2.2 in/ft

            sandy loams                                                    1.6-2.0 in/ft

            sands                                                               1.2-1.6 in/ft


    D. Evapotranspiration (ET) = evaporation + transpiration water use by crops

            1. ‘Potential’ ET (ETp) =


            2. Actual ET (ETa ) =


            3. Factors affecting ETa :




    E. Three mechanisms plants use to avoid drought stress:

            1. escape


            2. evade


            3. endure



    F.  Total water balance of a crop: 

            1. inputs:  rain, irrigation, snow melt, dew, upward wicking from subsoil


            2. outputs:   runoff, deep percolation, evaporation from soil surface, plant transpiration


IV. Water use efficiency of crops.

    A. Water Use Efficiency (WUE)  =   harvestable yield

                                                                cumulative ET


    B. Improving WUE of crops: many ideas here:

            1. High yielding varieties

            2. Mulches: 


            3. irrigation systems:

                        micro-irrigation  >  sprinkler  >  0 grade flood  >  furrow or flood


            4. crop rotations

            5. multiple inlets in flood or border

            6. ‘surge’ irrigation techniques in furrow

            7. conservation tillage systems

            8. fallow farming in semi-arid dryland systems

            9. sub-soiling fields with traffic pans

            10. terraces

            11. contour cultivation

            12. ‘water harvesting’ methods in orchards, horticulture plots in semi-arid regions

            13. weed control

            14. wind breaks

            15. soil test, optimum fertilization programs

            16. nematode and other disease and insect pest control

            17. others?


V. Irrigation scheduling.

    A. Soil-water sensors:         - tensiometers

                                                - neutron radiation

                                                - TDR sensors

                                                - ‘watermark’ type sensors


    B. Arkansas ‘Check Book’ method.  Examples will be performed in a laboratory exercise.