Water and Soil Water

  1. Large Quantities of water must be supplied to satisfy the requirements for plant growth

  2. Water is a solvent that makes up the soil solution

  3. Soil moisture affects soil air and soil temperature

  4. Surface water movement is the major cause of soil erosion

One of the most important functions a soil performs for a growing crop is catching and holding water. If a soil is unable to perform this function then it is of limited use for plant growth.

Plant Use of Water


Plants need water to form certain compounds - water is needed in photosynthesis to produce simple sugars -- only a small amount of the water used by the plant goes to photosynthesis. (1 -2%)

Waters main use in the plant is to act as a transportation system for nutrients and plant compounds -- (1)upward from the roots to the leaves and (2)downward from the leaves.

A measure of the quantity of water used by the plants is the amount of water required to produce 1 lb of dry matter. -- this is called the transpiration ratio


Other Functions of Water



The Hydrologic Cycle

Five processes - condensation, precipitation, infiltration, runoff, and evapotranspiration- make up the Hydrologic Cycle


Wetland Soils / Wet Soils


  1. Soil Drainage - refers to how rapidly exces water leaves a soil due to runoff or drainage through the soil.

    Conditions that can cause wetness

    1. impermeable clay soils

    2. flooded from runoff from higher elevations

    3. seeps

    4. high water table

      regional water table

      perched water table


    Effects of poor drainage

    1. Anaerobic conditions prevent growth of upland crops and other plants

    2. interferes with tillage and other land usage

  2. The term (jurisdictional) wetlands refers to areas that have special ecological values and functions and are protected by state or federal regulations.

    A wetland is an ecosystem that depends on constant or recurrent, shallow inundation or saturation at or near the surface long enough during the growing season to support vegetation adapted to life in saturated soils.

    Wetlands under natural (undisturbed) conditions must meet three criteria.
    wetland hydrology, hydric soil, hydrophytic vegetation.

    Sometimes the hydrophytic vegetation has been removed by farmers or developers. Farmland that would be classified today as wetland is referred to as prior converted wetland

    1. Wetland hydrology refers to the constant or recurrentshallow inundation or saturation at or near the surface of the substrate.

      1. Wetland hydrology must occur during the "growing season"

      2. In general, soils must be saturated to within 0 cm (1 ft) of the surface for approximately 14 days in most years.

    2. Hydric Soils are ones that have been saturated or water logged in most years, such that chemical reactions occurred that caused the soils to be anaerobic. Gray colors and/or mottling in the upper part of the soil are indicators of hydric soil.

    3. Hydrophytic Vegetation is adapted to saturated and anaerobic soils. Lists of wetland plant species are maintained to apply this criteria

  3. Wetland Protection

    1. Wetland Functions and Values

      1. Wetlands are considered valuable to society for several reasons:

        1. They provide wildlife habitat (food, shelter)

        2. improve quality of surface water by filtering sediment, trapping chemicals (P, pesticides)

        3. Store flood water


        Not all wetlands perform important functions, but deciding which need protection is controversial.

    2. Wetland protection in the U.S.

      1. Two agencies are currently invloved in protecting wetlands from destruction

        • U.S. Army Corps Engineers

        • Natural Resources Conservation Service

      2. The Corps Engineers protects wetlands on non-agricultural lands while the NRCS protects wetlands on agricultural fields.

      3. Wetlands that are along "navigable waters" cannot be filled in if the wetlands are non-navigable (low-flow or isolated) they can be filled in if less than 1 acre in size, and wetlands upto 10 acres in size can be partially filled if the Corps is notified in advance.

      4. in agricultural fields wetlands cannot be drained . Farmers who even plant crops on drained wetlands can lose government benefits.

  4. Wetland identification and Delineation

    1. Field Identification

      1. Most identification of wetlands is done to detemine if Federal protection laws are being violated.

      2. Wetland boundaries are identified ion the filed by determining the boundaries of hydric soils and hydrophytic vegetation.

      3. To delineate wetland boundaries, a knowledge of both soils and plants is necessary.

      4. Hydrology is difficult to determine in the filed without long term measurements


    2. Hydric Soils

      1. Hydric soils are identified primarily by looking for indicators

      2. indicators are certain soil color patterns or specific features that form in waterlogged soils.

  5. Wet soils are those that do not meet one or more of the criteria for the area to be a jurisdictional wetland but require artificial drainage for crop production or other uses.