Chapter 5 Soil Water Characteristics and Behavior Bringing

Chapter 5 Soil Water: Characteristics and Behavior Bringing water to arid valley soils. (R. Weil) THE NATURE AND PROPERTIES OF SOILS, 13/e Nyle C. Brady and Ray R. Weil © 2002 Pearson Education, Inc. Upper Saddle River, New Jersey 07458

Figure 5. 1 THE NATURE AND PROPERTIES OF SOILS, 13/e Nyle C. Brady and

Water Properties • Polarity – Charge difference across the water molecule • Adhesion – Attraction of water molecules to solids • Cohesion – Attraction of water molecules to themselves • Surface Tension – Water’s attraction to itself results in a surface film THE NATURE AND PROPERTIES OF SOILS, 13/e Nyle C. Brady and Ray R. Weil © 2002 Pearson Education, Inc. Upper Saddle River, New Jersey 07458

Figure 5. 2 THE NATURE AND PROPERTIES OF SOILS, 13/e Nyle C. Brady and

Figure 5. 3 Surface Tension THE NATURE AND PROPERTIES OF SOILS, 13/e Nyle C.

Figure 5. 4 THE NATURE AND PROPERTIES OF SOILS, 13/e Nyle C. Brady and

Capillary Action • Capillary Action – The water molecules are attracted to the sides of the solid and spread out in response to that attraction. • Best observed when putting a thin glass tube in water. THE NATURE AND PROPERTIES OF SOILS, 13/e Nyle C. Brady and Ray R. Weil © 2002 Pearson Education, Inc. Upper Saddle River, New Jersey 07458

Figure 5. 6 THE NATURE AND PROPERTIES OF SOILS, 13/e Nyle C. Brady and

Figure 5. 7 (a) THE NATURE AND PROPERTIES OF SOILS, 13/e Nyle C. Brady

Soil Water Potential • Soil Water Potential – The difference in energy levels between pure water in the reference state and soil water. – The difference in energy levels of water from one site or condition to another determines the direction and rate of water movement. THE NATURE AND PROPERTIES OF SOILS, 13/e Nyle C. Brady and Ray R. Weil © 2002 Pearson Education, Inc. Upper Saddle River, New Jersey 07458

Soil Water Potential – Gravitational Potential – The force of gravity acting on soil water attracts the water towards the center of the Earth – Submergence Potential – The positive hydrostatic pressure associated with the weight of water in a saturated soil – Matric Potential – The negative pressure due to the attractive force between water and the soil matrix – Osmotic Potential – The potential energy of water as it is reduced by the presence of solutes THE NATURE AND PROPERTIES OF SOILS, 13/e Nyle C. Brady and Ray R. Weil © 2002 Pearson Education, Inc. Upper Saddle River, New Jersey 07458

Figure 5. 8 THE NATURE AND PROPERTIES OF SOILS, 13/e Nyle C. Brady and

Figure 5. 9 THE NATURE AND PROPERTIES OF SOILS, 13/e Nyle C. Brady and

Figure 5. 10 THE NATURE AND PROPERTIES OF SOILS, 13/e Nyle C. Brady and

Measuring Water Content • Gravimetric Method – Taking a soil sample weighing, drying, then weighing the sample again to determine how much water was lost. • Neutron Scattering – Fast neutrons are emitted into the soil. When they collide with a hydrogen atom the neutron slows down and is counted. • Electromagnetic Method – Measures the reflection of electromagnetic signals by soil water. THE NATURE AND PROPERTIES OF SOILS, 13/e Nyle C. Brady and Ray R. Weil © 2002 Pearson Education, Inc. Upper Saddle River, New Jersey 07458

Figure 5. 14 Neutron Moisture Meter THE NATURE AND PROPERTIES OF SOILS, 13/e Nyle

Figure 5. 15 Time Domain Reflectrometer (TDR) THE NATURE AND PROPERTIES OF SOILS, 13/e

Measuring Soil Water Potential The tenacity with which water is held in the soils is an expression of soil water potential. • Tensiometers – Measure the attraction of water in the soil column by adhesion and cohesion. THE NATURE AND PROPERTIES OF SOILS, 13/e Nyle C. Brady and Ray R. Weil © 2002 Pearson Education, Inc. Upper Saddle River, New Jersey 07458

Figure 5. 16 THE NATURE AND PROPERTIES OF SOILS, 13/e Nyle C. Brady and

Preferential Flow • Preferential Flow – Water travels quickly down large soil pathways, such as connected macropores. – This leads to the quick disbursal of pesticides and other toxins into the soil and finally the groundwater. THE NATURE AND PROPERTIES OF SOILS, 13/e Nyle C. Brady and Ray R. Weil © 2002 Pearson Education, Inc. Upper Saddle River, New Jersey 07458

Infiltration and Percolation • Infiltration – The process by which water enters the soil pore spaces and becomes soil water. • Percolation – Once the water is in the soil, it moves through the soil column by percolation. • Wetting Front – A sharp boundary demarcating the transport of water through the column THE NATURE AND PROPERTIES OF SOILS, 13/e Nyle C. Brady and Ray R. Weil © 2002 Pearson Education, Inc. Upper Saddle River, New Jersey 07458

Figure 5. 26 Wetting Front 24 Hours After 5 cm of Rainfall THE NATURE

Figure 5. 27 THE NATURE AND PROPERTIES OF SOILS, 13/e Nyle C. Brady and

Figure 5. 29 THE NATURE AND PROPERTIES OF SOILS, 13/e Nyle C. Brady and

Soil Wetness • Saturation – When all of the soil pores are filled with water. • Field Capacity – Air instead of water occupies the macropores. Micropores and capillary pores are still filled with water. • Wilting Point – The time at which plants have removed all of the water from the capillary pores and no more available water remains in the soil. THE NATURE AND PROPERTIES OF SOILS, 13/e Nyle C. Brady and Ray R. Weil © 2002 Pearson Education, Inc. Upper Saddle River, New Jersey 07458

Figure 5. 32 THE NATURE AND PROPERTIES OF SOILS, 13/e Nyle C. Brady and

Figure 5. 33 THE NATURE AND PROPERTIES OF SOILS, 13/e Nyle C. Brady and

Cross-section of a Root Surrounded be Soil in Wet and Dry Conditions THE NATURE AND PROPERTIES OF SOILS, 13/e Nyle C. Brady and Ray R. Weil © 2002 Pearson Education, Inc. Upper Saddle River, New Jersey 07458