1

Soil Water Movement and Retention

Medium for plant growth

Regulator of water supplies

Recycler of raw materials

Habitat for soil organisms

Engineering medium

Functions of SoilFunctions of Soil

Functions of Soil

Medium for plant growth

Physical SupportGas exchangeWaterTemperatureNutrient source

2

Functions of Soil

Regulator of water supplies

InfiltrationRun-offStorage/MovementDistributionPurification

Integral to hydrologic cycle

Total Earth WaterTotal Earth Water

OceansOceansIce and Glaciers Ice and Glaciers Aquifer/GroundwaterAquifer/GroundwaterAtmosphereAtmosphere

LakesLakes

SoilSoilRiversRivers

97%2.0%0.6%0.2%0.012%0.001%0.0002%

Water Movement

3

Two Forces Responsible for Water Movement in Soils

Gravity

Capillarity

GravityGravity

4

Capillarity

Spontaneous movement of waterinto and through pore spaces in soil

without the aid of gravity.

Adhesion and Cohesion

Cohesion

5

Adhesion and CohesionAdhesion and Cohesion

oxygen

H

H

SURFACE

adhesion

oxygen

H

H

cohesion

Adhesion and CohesionAdhesion and Cohesion

adhesion

Cohesion(H-bonding)

Surface

Adhesion and Cohesion

Strong adhesion Weak adhesion

6

Weak Adhesion

Adhesion to Soil Particles

Strong Adhesive Forces

Soil PoresSoil PoresAdhesion and CohesionAdhesion to the tube or pore wallCohesion between water molecules

Tube wall

7

CapillarityCapillarity

Tube/Pore wall

}

Force down

h = 0.15r

CapillarityCapillarityh = 0.15

r

h

8

Soil Pores and Pore Size Distribution

TextureDensityStructure

Define.

Particle Size Large/coarse Medium Fine/SmallSand

Loamy SandSandy Loam

Silt

Sandy clay LoamSilty clay Loam

Silt LoamLoam

Clay LoamSandy ClaySilty Clay

Clay

Pore Size Large/Macro Meso/Medium Micro/Small

Capillarity Weak Moderate Strong

Texture

Soil Pores

Sandy Silty Clayey

9

Density

CompactionOrganic MatterArrangement of Particles Depth in Profile

Structure

10

Sand

Clay

Water

Sand Clay

Initial Saturation

Uncompacted Compacted

Initial Saturation

Sandy Loam

11

Aggregates

Wet Moist

Same Texture and Density

water

Relevance transpiration

12

impervious

Water Water