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Water retention curve is the relationship between the water content, θ, and the soil water potential, ψ. The soil moisture curve is characteristic for different types of soil, and is also called the soil moisture characteristic. It is used to predict the soil water storage, water supply to the plants (field capacity) and soil aggregate stability.
Water moves through soil due to the force of gravity, osmosis and capillarity. At 0 to 33 kPa suction (field capacity), water is pushed through soil from the point of its application under the force of gravity and the pressure gradient created by differences in the pressure of water; this is called saturated flow. At higher suction, water ...
Suction pressure (J/kg or kPa) Typical water content (vol/vol) Conditions Saturated water content θ s: 0 0.2–0.5 Fully saturated soil, equivalent to effective porosity: Field capacity: θ fc: −33 0.1–0.35 Soil moisture 2–3 days after a rain or irrigation Permanent wilting point: θ pwp or θ wp: −1500 0.01–0.25
The Richards equation represents the movement of water in unsaturated soils, and is attributed to Lorenzo A. Richards who published the equation in 1931. [1] It is a quasilinear partial differential equation; its analytical solution is often limited to specific initial and boundary conditions. [2]
The Universal Soil Loss Equation (USLE) is a widely used mathematical model that describes soil erosion processes. [1]Erosion models play critical roles in soil and water resource conservation and nonpoint source pollution assessments, including: sediment load assessment and inventory, conservation planning and design for sediment control, and for the advancement of scientific understanding.
Base-cation saturation ratio (BCSR) is a method of interpreting soil test results that is widely used in sustainable agriculture, supported by the National Sustainable Agriculture Information Service (ATTRA) [1] and claimed to be successfully in use on over a million acres (4,000 km 2) of farmland worldwide.
When the water pressure at a point in the soil is equal to the total vertical stress at that point, the effective stress is zero and the soil has no frictional resistance to deformation. For a surface layer, the vertical effective stress becomes zero within the layer when the upward hydraulic gradient is equal to the critical gradient. [ 15 ]
The available volume for additional water in the soil depends on the porosity of the soil [7] and the rate at which previously infiltrated water can move away from the surface through the soil. The maximum rate at that water can enter soil in a given condition is the infiltration capacity.