Lecture 5: Soil Water- Characteristics and Behavior

Question 1

Saturated flow (percolation)

Answer 1

takes place in micropores when they are completely filled/saturated with water
-follows gradients in the gravitational potential of soil water (Wg)

Question 2

Unsaturated flow

Answer 2

occurs when larger pores in soil are filled with air, leaving only smaller pores to hold and transmit water.
-mainly driven by matric potential (Wm)

Question 3

Darcy’s Law

Answer 3

describes the flow of water in saturated soils (top to bottom)

Question 4

Darcy’s Law equation

Answer 4

(Q/t) = (Aksat(W1-W2)) / L

Question 5

How does speed and spread of saturated flow differ with soil texture?

Answer 5

Flow is slower for finer texture like clay and takes hours. Coarser textures like sandy loam takes significantly less time.

Question 6

Role of macropores in percolation and contaminant transport

Answer 6

macropores are preferential flow pathways
-mostly made by roots or organisms like worms
-increases the risk of groundwater contamination

Question 7

Explain how changes in texture affects unsaturated flow

Answer 7

Abrupt changes from fine to coarse soil texture within a soil profile interrupts unsaturated flow and causes water logging

Question 8

How does water vapor move along gradients

Answer 8

warmer to cooler soils
fresher to saline soils

Question 9

What gradients does water vapor move through

Answer 9

temperature, salinity, and moisture in soils

Question 10

Saturated flow W

Answer 10

W= 0 kPa

Question 11

Unsaturated flow W

Answer 11

W < -1kPa

Question 12

Discuss how the amount of plant-available water differs with texture

Answer 12

Loams and siltier clay loams are the best textures for holding plant available water. Clay holds the water too tightly and sand does not store that much water because of the larger pores

Question 13

Saturated soil wetness and soil water potential

Answer 13

all the pore space is filled with water
W=0kPa

Question 14

Field capacity soil wetness and soil water potential

Answer 14

after all free draining water has been taken by gravity W=-10kPa

Question 15

Wilting coefficient soil wetness and soil water potential

Answer 15

Little bit of water in pore space and most is air. Plants have difficult time extracting water from soil W=-1500kPa

Question 16

Hygroscopic coefficient soil wetness and soil water potential

Answer 16

mostly air in the pore space and most of the water is tightly held by the clay particles and cannot be removed without destroying the soil.
W=-3,100kPa