Outline:

  1. Soil properties that affect plant available water

  2. Management of soil water

  3. Permeability (review)

 

  1. Factors that affect plant- available water

    The factors that control water available to the plant are very important because some can be managed.

    These factors include::

    1. soil texture
    2. soil consistence
    3. soil structure
    4. organic matter
    5. Bulk Density

    The amount of water held at field capacity is not the same for all soils -- it depends on the amount of micropores.

    Texture and soil water retention
    • micropores are spaces formed between sand, silt, and clay particles.
    • size and number of micropores depends on the size of the soil particles.
    • as clay content increases micropores are smaller and the total pore space is greater
    • as the sand content increases larger pores dominate and the total pore space is less

    micropores in clay exert greater force on water than micropores of sand.

    In clay there is more surface are to attract the water and hold it tighter.
  2. Soil Water Management

    The key to efficient water use is to reduce water losses from the soil and increase the plant use-efficiency.
    1. Increase infiltration
      1. terraces
      2. strip crops
      3. enhance soil structure
      4. add mulches
      5. organic residue

    2. Decrease evaporation from soil surface
      1. spacing of plants to provide quick canopy cover
      2. plastic covering
      3. shading
      4. mulch
    3. Evapotranspiration
        1. Selection of plant species or cultivars
        2. Increase plant use efficiency
        3. Reduce transpiration
        • remove weeds and grasses from growing crops
          Weight of Weeds Weight of soybeans
          6 lbs / A weeds 2130 lbs / A
          1250 lbs / A weeds 1310 lbs / A

           

          1. Planting date
          2. Plant breeding
          3. Maximum rooting depth
          4. Plant crops on suitable soil
            1. coastal bermuda - on deep sands
            2. tobacco on well drained soils
            3. corn on wetter soils

           

      4. Adequate Ferilizer

      No fertilizer Fertilizer
      Corn yield (Bu) 18 79
      Total water - in 14.1 16
      Water - gal / bu 21,000 5,600
5. remove excess water by surface or subsurface drainage
6. get water to depth with vertical mulching

7. anything that enhances water infiltration


8. plant crops at proper time to utilize seasonal rainfall

9. plant varieties adapted to meet water available conditions
10. any factor that affects plant growth will affect water use and efficiency.
    1. Permeability and Other Soil Water Factors

      The type and distribution of soil pores control a number of different soil - water relationships:
      1. Infiltration - rate at which water enters the soil. This is important from the standpoint of erosion.
      2. Hydraulic Conductivity - movement of water through the soil when it is saturated
      3. Soil drainage class - the depth and duration of saturation
      4. Plant available water holding capacity - water that is available to the plant