Soil Water. At the end of class, student are expected to have ability to: Discuss and describe soil-water-plant relationship. Analyze hydraulic properties of soils and flow of water into and through soil. Assess the equipment for soil water technique. Outline. Water and Plant Growth
At the end of class, student are expected to have ability to:
Discuss and describe soil-water-plant relationship.
Analyze hydraulic properties of soils and flow of water into and through soil.
Assess the equipment for soil water technique
Tissue composition50–90% water
Nutrient transport within plants
Chemical reactions – as solvent
Ease of root growth
Water shortage causes plant growth inhibition and wilting.
Excess water causes oxygen and nutrient deficiencies, susceptibility to fungi, toxin build-up, and root damage.
- difficult to flow
- low permeability
- easy to flow
- high permeability
Analyze the soil water holding capacity
Determinemethods of soil water measurements and their advantages and limitations,
2) Capillary Water is held by cohesive forces greater than gravity and is available to plants
3) Gravitational Water is that water which cannot be held against gravity as water is pulled down through the soil, nutrients are "leached" out of the soil (nitrogen)
Gravitational water is the water that fills macropores. This water drains quickly.
Source: Kaufmann, Robert K. and Cleveland, Cutler J. 2007. Environmental Science (McGraw-Hill, Dubuque, IA).
AWC = FC − PWP
Available water content = water content at field capacity - water content at permanent wilting point
The field capacity, permanent wilting point (PWP) and available water content are called the soil moisture characteristics.
Using the table provided below, the RAW stored within the effective root zone for a soil can be calculated by measuring the thickness of each soil layer (in meters or parts of a meter) determining the soil texture of each layer, and then multiplying the thickness by the appropriate RAW Value.
General relationship between soil water characteristics and soil texture. Note that the wilting coefficient increases as the texture becomes finer. The field capacity increases until we reach the silt loams, then levels off. Remember these are representative curves; individual soils would probably have values different from those shown.
Water holding capacity (mm/cm depth of soil) of main texture groups. Figures are averages and vary with structure and organic matter differences.
Θa is the antecedent or actual field moisture content,
PWPΘ is the volumetric moisture content at the PWP,
d is depth of the corresponding horizon.
Obtain the sum total of AWCactual for all horizons.
where FCΘ and PWPΘ represent volumetric field capacity and permanent wilting point, and d is depth of the horizon. Obtain sum total of AWCpotential for all horizons.
1. How deep will 7 cm of rain penetrate?
2. How much irrigation is needed to bring the soil profile of 100 ha farm to Θfc?
Measuring Soil Water Content
Measuring Soil Water Potential
Gravimetric measurements include:
1. Energy per unit volume is expressed as ergs/cm2, dynes/cm2, N/m2,
2. Energy per unit mass is expressed as ergs/g or J/kg, and
3. Energy per unit weight is expressed in terms of height of water as cm or m.