Module 11: Water and Soils Flashcards
What is pore volume?
Space taken up by air and water in the soil
What is porosity?
Percentage of air and water volume in soil
What is infiltration or drainage?
The downward movement of water into the soil
What is infiltration rate?
Speed of which water moves into a soil (mm/hr)
Greater in sand than clay
What is saturated soil?
All pores in the soil are filled with water
What is gravitational water?
Water that drains or moves down the soil profile due to gravity.
Volume of water between saturation and field capacity = gravitational water
Not usually available to plants
What is soil at field capacity?
Soil after the removal of gravitational water
It contains the maximum amount of water available to plants
What is capillary water?
Water retained in soil pores after removal of gravitational water
Surface tension (suction) holds the water around the soil particles
What is the permanent wilting point?
Point at which the plant can no longer absorb any water.
As some capillary water is removed by evaporation and plant absorption, surface tension increases until the plant can no longer absorb water.
The force holding water to soil particles is stronger than roots’ absorption force.
What is the available water capacity?
Volume of water that can be used by the plant.
The volume of water between field capacity and permanent wilting point
What is the groundwater table?
Top of the layer/top boundary of the permanently saturated soil
What is a perched groundwater table?
Top of a water layer/top boundary above the impermeable layer (hardpan) and is near the soil surface (20 to 100cm)
What is a capillary rise?
Upward movement of water
In clay, it rises slower but rises a greater distance. In sand, it rises faster but rises a shorter distance
What are the two ways water is added to the soil?
Rainfall and irrigation
What are the ways water is removed from the soil?
Transpiration, evaporation, drainage, and surface runoff
What are the factors that affect the infiltration rate?
Soil texture, soil moisture content, soil structure
If the soil feels wet, what does that say about the soil water content?
Higher than field capacity
If the soil feels moist, what does that say about the soil water content?
Between field capacity and permanent wilting point
If the soil feels dry, what does that say about the soil water content?
Below permanent wilting point
How do you measure the moisture content in soil?
Sample is weighed and dried for 24 hours in an oven at 105C then weighed again
% water = weight of moist soil - weight of oven dried soil) / weight of oven dry -> everything multiplied by 100%
What determines the depth of the groundwater table?
It varies according to location especially due to topography.
In one place, it can vary in time (temperature, etc)
What is the soil moisture content?
Percentage of mass of soil that is made up of water
How do you calculate porosity?
Pore volume is divided by soil volume. Multiplied by 100%
