T7-1 Soil Science & Management, 4E

Chapter 7

Soil Water

T7-2 Soil Science & Management, 4E

Objectives

• Identify the role of water in plant growth

• Define the forces that act of soil water

• Classify types of soil water

• Discuss how water moves in the soil

• Explain how plant roots remove water from the soil

• Describe how to measure soil water content

T7-3 Soil Science & Management, 4E

Terms to Know• Adhesion• Adhesion water• Anaerobic• Available water• Bar• Capillary• Capillary rise• Capillary water• Cohesion

• Cohesion water• Field capacity• Gravimetric water

content• Gravitational flow• Gravitational potential• Gravitational water• Hydrogen bond

T7-4 Soil Science & Management, 4E

Terms to Know• Hygroscopic water• Matric potential• Osmotic potential• Permanent wilting

point• Potentiometer• Preferential flow• Resistance block• Saturated flow

• Saturation• Soil-moisture tension• Soil-potential• Temporary wilting

point• Unsaturated flow• Volumetric water

content• Water content

T7-5 Soil Science & Management, 4E

How Plants Use Water

• Effect of water stress

• Effect of excess water

T7-6 Soil Science & Management, 4E

Forces on Soil Water

Figure 7-2

T7-7 Soil Science & Management, 4E

Forces on Soil Water

• Capillarity

Figure 7-3

T7-8 Soil Science & Management, 4E

Forces on Soil Water

• Soil-water potential

Figure 7-4

T7-9 Soil Science & Management, 4E

Forces on Soil Water

Figure 7-5

T7-10 Soil Science & Management, 4E

Types of Soil Water

• Available water

Figure 7-6

T7-11 Soil Science & Management, 4E

Water Retention and Movement

• Water retention

Figure 7-8

T7-12 Soil Science & Management, 4E

• Water movement

Figure 7-9

Water Retention and Movement

T7-13 Soil Science & Management, 4E

• The wetting front• Capillary rise• Effect of soil horizons (See Figure 7-11)

• Preferential flow

Figure 7-11

Water Retention and Movement

T7-14 Soil Science & Management, 4E

How Roots Gather Water

Figure 7-12

T7-15 Soil Science & Management, 4E

How Roots Gather Water

• Pattern of water removal

Figure 7-13

T7-16 Soil Science & Management, 4E

Measuring Soil Water

• Gravimetric measurements– Weight basis– Soil depth basis

T7-17 Soil Science & Management, 4E

Measuring Soil Water

• Potentiometers

Figure 7-14

T7-18 Soil Science & Management, 4E

Measuring Soil Water

• Resistance blocks

• Neutron probe

Figure 7-17

T7-19 Soil Science & Management, 4E

Summary

• Not unlimited resource

• Conservation important

• Improve water-use efficiency

• Lower evapotranspiration

• Pay attention to possible pollution sources