AGEN 2363 notes:  Chpt. 15.  Irrigation and Reclamation.


I. Advantages of irrigation.

            1. less risk of crop failure due to drought

            2. more consistent yields

            3. increased yields most seasons, especially in semi-arid, arid regions

            4. crop loan acquisition benefits

            5. increased land value

            6. reclamation of salty soils (if water is less salty!)


II. Disadvantages of irrigation.

            1. investment costs

            2. maintenance costs

            3. water source: reliability? reclamation/retrieval of water?

            4. ponding/crop damage

            5. may not pay off in some years


III. Types of irrigation systems:

     A. flood


     B. furrow:  see TABLE 15-2.  Suggested Maximum Lengths of Cultivated Furrows


     C. sprinkler:

            - center pivot: low-evap. drop-down nozzles

            - lateral

            - solid set

            - ‘big-gun’


     D. micro-irrigation

            - underground drip-lines

            - surface drip tape

            - micro-emitters (vineyards, orchards, greenhouses)


     E. Factors affecting design of irrigation systems:

            1. type of crop

            2. water source: availability, quality

                        - EC = electrical conductivity = measure of water salinity: units: mmhos/cm

            3. landscape

            4. soil texture, aggregation,

            5. restrictive layers in the subsoil

            6. maintenance requirements, feasibility

            6. $$$





IV.  Irrigation scheduling.

     A. Factors affecting timing and rates of irrigation:

            1. crop:  species, growth stage

            2. soil: water holding capacity, moisture content

            3. water output of system

            4. weather: temperatures (daily high, low), wind, sunlight

            5. health of crop

            6. potential returns, profitability


     B. Methods.

            1. ‘feel’

            2. soil-water sensors:

                        - ceramic tensiometers

                        - non-ceramic resistance sensors

                        - ceramic resistance sensors

                        - neutron moisture meters

                        - time domain refectrometry (TDR) sensors

                        - thermocouple psychrometers

            3. crop light reflectance in IR wavelengths

            4. computer models:

                        - Arkansas Irrigation Scheduler

            5. calendar scheduling


V. Increasing water use efficiency of crops.

            1. precision land leveling

            2. micro-irrigation

            3. multiple inlet systems

            4. mulches – artificial:   plastic, bark, shredded wood or paper,

            5. mulches – natural: conservation or no-till

            6. proper soil fertility/fertilization program

            7. high yielding varieties

            8. keep stress from insects, diseases, and other plant injury at a minimum

            9. timing of applications!

            10. uniformity of application – both across the field and into the soil profile!