Section 4a

Question 1

Horizon definition

Answer 1

Soil formation results in the natural development of layers within a
profile. Each layer is composed of structural units consisting of various fractions of sand, silt, clay
and organic matter. Each layer is called a HORIZON

Each soil horizon would likely have
differing:
* Color
* Particle size
* Density
* Hydraulic conductivity
January 21, 2025 4

Question 2

Primary soil structure

Answer 2

refers to the size
distribution of
individual particles
(sand, silt, clay

Question 3

Secondary Soil Structure

Answer 3

Secondary structure
refers to arrangement
of particles into larger
aggregates
* Secondary structure
can a have large
influence on water
movement
January 21, 2025 5Tindall and Kunkell (1999)

Question 4

hydrualic gradient

Answer 4

In the saturated zone, flow is driven by a gradient in positive pore pressure, whereas in the unsaturated zone, flow is driven by a gradient in negative matric potentials

The hydraulic gradient (
𝑖
i) is the slope of the water pressure or energy driving water flow through a porous medium (soil, rock, or pipes).

It represents how water moves from high energy (pressure) to low energy (pressure).
It is the driving force behind groundwater flow and infiltration.

The hydraulic gradient (
𝑖
i ) describes how water flows through soil, rock, or pipes due to differences in energy levels. It is a measure of how much pressure or elevation difference exists over a given distance.

Think of it like a slide:

If a slide is steep, you go down faster (high hydraulic gradient).
If the slide is shallow, you go down slower (low hydraulic gradient).
If the slide is flat, you don’t move at all (zero hydraulic gradient).

Question 5

What do tensiometers measure

Answer 5

Matric potential and hydraulic gradients in the unsaturated zone are measured using tensiometers
Matric potential (Ψ) is the suction force or energy that holds water in soil due to adhesion between water molecules and soil particles.

It represents how tightly water is bound to soil particles.
It is always negative because water is held by capillary forces.
The drier the soil, the more negative the matric potential (stronger suction).

Question 6

Infiltration Capacity (fp)

Answer 6

Theoretical maximum rate
of water transmission into
soil as influenced by soil
factors

Question 7

Infiltration Rate (f)

Answer 7

Rate of water transmission into soil as influenced by soil factors and the water availability at the soil surface