Soil Water Processes:Chapter 3Soil Water Processes:Chapter 3

Learn how soil properties influence runoff, Learn how soil properties influence runoff, infiltration and plant growth.infiltration and plant growth.

Learn some of the common terms that are used Learn some of the common terms that are used to describe soils profiles and soil properties.to describe soils profiles and soil properties.

Learn about the main processes that occur Learn about the main processes that occur when a soil wets and drys.when a soil wets and drys.

Learn how to quantify the amount of water Learn how to quantify the amount of water that is stored in the soil and how this amount that is stored in the soil and how this amount changes with time.changes with time.

Soil TextureSoil Texture

Figure 3.1

Figure 3.2

Textural Triangle

TermsTerms

Voids/PoresVoids/Pores SaturatedSaturated

Figure 3.3

Soil MatrixSoil Matrix

Porosity Porosity Equation 3.3Equation 3.3

tVsV

1tVvV

n

Volumetric Soil Water ContentVolumetric Soil Water ContentEquation 3.4Equation 3.4

t

wv V

Vθ

Volumetric Soil Water Content=Vw/VtVolumetric Soil Water Content=Vw/Vt

Degree of SaturationDegree of SaturationEquation 3.5Equation 3.5

n Sθv

Gravimetric Soil Water ContentGravimetric Soil Water ContentEquation 3.6Equation 3.6

s

wg m

mθ

Gravimetric Soil Water Content=mGravimetric Soil Water Content=mww/m/mss

TermsTermsBulk DensityBulk Density

Mass of soil per unit volumeMass of soil per unit volume Density of soil particles usually near 165 Density of soil particles usually near 165

lb/ftlb/ft33 or 2.65 g/cm or 2.65 g/cm33

Compare different soilsCompare different soils

Bulk DensityBulk DensityEquation 3.8Equation 3.8

t

tb V

mρ

Dry Bulk DensityDry Bulk DensityEquation 3.10Equation 3.10

n)(1ρρ pdry

TermsTerms

Tension-infiltrationTension-infiltration Adhesion, Cohesion, Capillary, Suction ForcesAdhesion, Cohesion, Capillary, Suction Forces

Gravity-infiltrationGravity-infiltration Small pores vs. Large poresSmall pores vs. Large pores Field capacity & Wilting pointField capacity & Wilting point

Water RetentionWater Retention

Figure 3.4

HysteresisHysteresis

Figure 3.5

Plant Response to Soil-Water ContentPlant Response to Soil-Water Content

Figure 3.10

Plant Available Water Plant Available Water versus Textureversus Texture

Figure 3.5

Soil-Water RelationshipsSoil-Water Relationships

Figure 3.6

Fig. 3.16

Factors Affecting Water Movement in Soils

Estimating Infiltration RatesEstimating Infiltration Rates

Empirical MethodsEmpirical Methods Horton and Green-Ampt EquationsHorton and Green-Ampt Equations

Physical Based MethodsPhysical Based Methods Darcy’s LawDarcy’s Law Flow related to hydraulic gradient and soil typeFlow related to hydraulic gradient and soil type

Seasonal Soil Water Balance

SM P IR Q G ET

SM is the change in soil water storage in the soil profileP is precipitationIR is irrigationG is percolation waterET is evapotranspirationQ is surface runoff

Fig. 3.23

Seasonal Soil Water Balance in Ohio

Fig. 4.1

Fig. 4.4

Fig. 4.5

Fig. 4.6

Annual Pan Evaporation in the USAAnnual Pan Evaporation in the USA