Water and Soil Water
Large Quantities of water must be supplied to satisfy the requirements for plant growth
Water is a solvent that makes up the soil solution
Soil moisture affects soil air and soil temperature
- 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
It takes 500 lbs of water to produce 1 lb of wheat
It takes 850 lbs of water to produce 1 lb of alfalfa
- It takes 300 lbs of water to produce 1 lb of grain sorghum
Other Functions of Water
The movement and retention of water by soil influences soil management practices and construction designs.
Also of importance is the interaction of soil water and chemicals, this is of concern for ground water pollution.
- In many areas of the world the quantity of water available for drinking and irrigation is slight; learning how water interacts with the soil is important to water efficiency.
- The total supply of water on the earth is constant - it doesn't increase
- Throughout history, water has been recycled; it is used, disposed of,
purified, and used again.
- The recycling of water through a series of processes is called the hydrologic
cycle or the water cycle.
Five processes - condensation, precipitation, infiltration, runoff, and evapotranspiration- make up the Hydrologic Cycle
Condensation is the process of water changing from a vapor to a liquid.
Precipitation is water being released from clouds as rain, sleet, snow, or hail.
Precipitation begins after water vapor, which has condensed in the atmosphere,
becomes too heavy to remain in atmospheric air currents and falls.
Infiltration - A portion of the precipitation that reaches the Earth's surface seeps into the ground.
Runoff. - Precipitation that reaches the surface of the Earth but does not infiltrate the soil.
Evapotranspiration is water evaporating from the ground and transpiration by plants.
Evapotranspiration is also the way water vapor re-enters the atmosphere.
In humid regions, precipitation exceeds evapotranspiration. In arid and semi-arid regions, evapotranspiration exceeds precipitation.
Wetland Soils / Wet Soils
Soil Drainage - refers to how rapidly exces water leaves a soil due to runoff or drainage through the soil.
Conditions that can cause wetness
impermeable clay soils
flooded from runoff from higher elevations
high water table
regional water table
perched water table
Effects of poor drainage
Anaerobic conditions prevent growth of upland crops and other plants
interferes with tillage and other land usage
- impermeable clay soils
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
Wetland hydrology refers to the constant or recurrentshallow inundation or saturation at or near the
surface of the substrate.
Wetland hydrology must occur during the "growing season"
- In general, soils must be saturated to within 0 cm (1 ft) of the surface for approximately 14 days in most years.
- Wetland hydrology must occur during the "growing season"
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.
- Hydrophytic Vegetation is adapted to saturated and anaerobic soils. Lists of wetland plant species are maintained to apply this criteria
- Wetland hydrology refers to the constant or recurrentshallow inundation or saturation at or near the surface of the substrate.
Wetland Functions and Values
Wetlands are considered valuable to society for several reasons:
They provide wildlife habitat (food, shelter)
improve quality of surface water by filtering sediment, trapping chemicals (P, pesticides)
Store flood water
Not all wetlands perform important functions, but deciding which need protection is controversial.
- They provide wildlife habitat (food, shelter)
- Wetlands are considered valuable to society for several reasons:
Wetland protection in the U.S.
Two agencies are currently invloved in protecting wetlands from destruction
U.S. Army Corps Engineers
- Natural Resources Conservation Service
- U.S. Army Corps Engineers
The Corps Engineers protects wetlands on non-agricultural lands while the NRCS protects wetlands on
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.
- in agricultural fields wetlands cannot be drained . Farmers who even plant crops on drained wetlands can lose government benefits.
- Two agencies are currently invloved in protecting wetlands from destruction
- Wetland Functions and Values
Wetland identification and Delineation
Most identification of wetlands is done to detemine if Federal protection laws are being violated.
Wetland boundaries are identified ion the filed by determining the boundaries of hydric soils and
To delineate wetland boundaries, a knowledge of both soils and plants is necessary.
Hydrology is difficult to determine in the filed without long term measurements
- Most identification of wetlands is done to detemine if Federal protection laws are being violated.
Hydric soils are identified primarily by looking for indicators
- indicators are certain soil color patterns or specific features that form in waterlogged soils.
- Hydric soils are identified primarily by looking for indicators
- Field Identification
- 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.