Final Study Guide - Soil Water Flashcards
What is soil water potential and how is it related to the water content?
Soil-water potential is a measure of the potential energy per unit mass, volume, or weight of soil water, compared with that of pure, free water
The lower the water content, the harder it is to pull water out of the soil. The higher water content results in higher, less negative water potential, while lower water content results in lower, more negative water potential
What are the forces (potentials) driving water potential in soils?
Ψtotal = Ψg + Ψm + Ψo + Ψp
What is the water potential at: saturation, field capacity, permanent wilting point?
Saturation: 0 bar
Field capacity: -0.1 to -0.3 bar
Permanent wilting point: -15 bar
How is available water calculated? Why is this a more useful value for plant growth than field capacity and wilting point?
Available water = field capacity - permanent wilting point
More useful than either because it shows the amount of soil water in soil that is available for plants to use
How does texture drive available soil water content? What texture will have higher content of plant available water: sandy, loamy or clay loam?
Coarse textured soils have the least PAW because they mostly have large pores with limited ability to retain water
Fine textured soils have moderate PAW because they have many micropores, though much of the water held in them is unavailable
Loamy textured soils have the most PAW because they have a mix between micro and macropores
How does soil structure drive plant available water content?
It can increase plant available water by increasing/decreasing porosity to a point
It also affects how water infiltrates and percolates through soil
What is infiltration?
A process by which water enters the soil pore spaces and becomes soil water
How does soil texture drive saturated hydraulic conductivity? Which texture has higher saturated hydraulic conductivity? Sand, silt loam or silty clay?
Saturated hydraulic conductivity: When infiltration rate becomes constant due to saturation
Sandy soils have the highest saturated hydraulic conductivity
What is runoff?
Water that runs off of soil surface (instead of infiltration)
What is percolation?
Movement of water through the soil profile
Water flows from _____ (higher/lower) to ______ (higher/ lower) total potential energy
Water flows from higher to lower total potential energy
How to measure saturated flow (Darcy’s Law) and unsaturated flow
What potentials are considered in both?
Saturated flow: Gravity and pressure
Unsaturated flow: Matric
What causes preferential flow paths, what are impacts
Various factors, which can include soil fauna, plant roots, cracks in soil, and various other reasons
This means water does not saturate soil uniformly
What is relationship between water flow in soil and in plant?
Water moves from soil to plant because it moves from higher (less negative) to lower (more negative) water potential
What is soil water budget and what factors influence it?
Imagine soil water budget as a bucket model.
S = (P + I) - (R + ET + D)
P: Precipitation
I: Irrigation
ET: Evapotranspiration
R: Runoff
D: Deep percolation = discharge
