©2002 Pearson Education, Inc. Upper Saddle River, New Jersey THE NATURE AND PROPERTIES OF SOILS, 13/e Nyle C. Brady and Ray R. Weil Chapter 7 Soil Aeration and Temperature Sun-warmed soil ridges. (R. Weil)

©2002 Pearson Education, Inc. Upper Saddle River, New Jersey THE NATURE AND PROPERTIES OF SOILS, 13/e Nyle C. Brady and Ray R. Weil Soil Aeration Oxygen availability is controlled by –Soil macroporosity (as affected by texture and structure) –Soil water content (as it affects water/air ratio) –Oxygen consumption by respiration (Including plant roots and microorganisms)

©2002 Pearson Education, Inc. Upper Saddle River, New Jersey THE NATURE AND PROPERTIES OF SOILS, 13/e Nyle C. Brady and Ray R. Weil Soil Aeration Poor aeration occurs when 80% to 90% of the soil pore space is filled with water. –Results in little air storage in the soil –Mainly cuts off pathways of gas exchange with the atmosphere –Compaction can also result in a loss of gas exchange with the atmosphere

©2002 Pearson Education, Inc. Upper Saddle River, New Jersey THE NATURE AND PROPERTIES OF SOILS, 13/e Nyle C. Brady and Ray R. Weil Soil Aeration When the soil has an extreme amount of excess water it is water saturated or waterlogged. Hydrophytes are plants that have ways of obtaining oxygen in waterlogged soils –Some grasses use aerenchyma tissues to transport oxygen down the stem to the roots –Some trees such as mangrove and baldcypress produce aerial roots to obtain oxygen

©2002 Pearson Education, Inc. Upper Saddle River, New Jersey THE NATURE AND PROPERTIES OF SOILS, 13/e Nyle C. Brady and Ray R. Weil Figure 7.1 Mangroves on the coast of the Indian Ocean.

©2002 Pearson Education, Inc. Upper Saddle River, New Jersey THE NATURE AND PROPERTIES OF SOILS, 13/e Nyle C. Brady and Ray R. Weil Figure 7.2 Sugar beets in a clay loam soil. You can see where the beets are dying out in a compacted area that is water saturated. Pine trees dying in sandy soil that was flooded as a result of a beaver dam.

©2002 Pearson Education, Inc. Upper Saddle River, New Jersey THE NATURE AND PROPERTIES OF SOILS, 13/e Nyle C. Brady and Ray R. Weil Figure 7.3 Diffusion of gases over a membrane do to a partial pressure gradient.

©2002 Pearson Education, Inc. Upper Saddle River, New Jersey THE NATURE AND PROPERTIES OF SOILS, 13/e Nyle C. Brady and Ray R. Weil Oxygen in Soil Atmospheric concentrations 78% Nitrogen (N 2 ) 21% Oxygen (O 2 ) 0.035% Carbon Dioxide (CO 2 ) Soil oxygen varies from about 20% near the surface to less than 5% at depth. During respiration in soils, oxygen is replaced with carbon dioxide, which could approach toxic levels When soil oxygen becomes low it results in anaerobic conditions

©2002 Pearson Education, Inc. Upper Saddle River, New Jersey THE NATURE AND PROPERTIES OF SOILS, 13/e Nyle C. Brady and Ray R. Weil Other Gases in Soil CO 2 and O 2 have an inverse relationship in the soils Water vapor (H 2 O) is usually close to the saturation level in soils When soils are water logged, methane (CH 4 ) and hydrogen sulfide (H 2 S) can build up Under anaerobic conditions ethylene (C 2 H 4 ) is produced and can be very toxic to plant roots

©2002 Pearson Education, Inc. Upper Saddle River, New Jersey THE NATURE AND PROPERTIES OF SOILS, 13/e Nyle C. Brady and Ray R. Weil Oxygen Concentrations in a Wet Soil Aggregate of an Aquic Hapludoll

©2002 Pearson Education, Inc. Upper Saddle River, New Jersey THE NATURE AND PROPERTIES OF SOILS, 13/e Nyle C. Brady and Ray R. Weil

©2002 Pearson Education, Inc. Upper Saddle River, New Jersey THE NATURE AND PROPERTIES OF SOILS, 13/e Nyle C. Brady and Ray R. Weil Figure 7.12

©2002 Pearson Education, Inc. Upper Saddle River, New Jersey THE NATURE AND PROPERTIES OF SOILS, 13/e Nyle C. Brady and Ray R. Weil Figure 7.13 Even a thin layer of soil deposited on a trees root system can suffocate the roots. A drywell can be constructed to protect the root system of the tree.

©2002 Pearson Education, Inc. Upper Saddle River, New Jersey THE NATURE AND PROPERTIES OF SOILS, 13/e Nyle C. Brady and Ray R. Weil Figure 7.14 Core cultivation removes soil plugs to increase the aeration of compacted soils. The plugs are removed from the soil but left on site to dissolve back into the soil.

©2002 Pearson Education, Inc. Upper Saddle River, New Jersey THE NATURE AND PROPERTIES OF SOILS, 13/e Nyle C. Brady and Ray R. Weil Soil Temperature The temperature of soil affects physical, biological, and chemical processes –Cold temperatures slow chemical reactions –Cold temperatures slow biological decomposition which slows the production of nitrogen, phosphorous, sulfur, and calcium –High temperatures can also inhibit biological activity or kill off microorganisms

©2002 Pearson Education, Inc. Upper Saddle River, New Jersey THE NATURE AND PROPERTIES OF SOILS, 13/e Nyle C. Brady and Ray R. Weil Soil Temperature Warm soil temperatures generally induce plant germination and growth Seeds of plants that are adapted to open gaps react to warm soil temperatures caused by direct solar radiation Seeds of prairie grasses require a cold period to enable them to germinate. This is called vernalization. Some plants, such as tulips, require chilling in early winter to develop buds

©2002 Pearson Education, Inc. Upper Saddle River, New Jersey THE NATURE AND PROPERTIES OF SOILS, 13/e Nyle C. Brady and Ray R. Weil Soil Temperature Soil microbial activity and organic matter decomposition cease below 5ºC which is known as biological zero Clear plastic can be used to raise soil temperatures reducing fungal diseases and control pests, called soil solarization.

©2002 Pearson Education, Inc. Upper Saddle River, New Jersey THE NATURE AND PROPERTIES OF SOILS, 13/e Nyle C. Brady and Ray R. Weil Figure 7.18

©2002 Pearson Education, Inc. Upper Saddle River, New Jersey THE NATURE AND PROPERTIES OF SOILS, 13/e Nyle C. Brady and Ray R. Weil Soil Temperature Frost heave occurs as a result of the formation of ice lenses in the soil. –Water from the unfrozen soil gets attracted to the ice lenses, “jacking-up” the objects

©2002 Pearson Education, Inc. Upper Saddle River, New Jersey THE NATURE AND PROPERTIES OF SOILS, 13/e Nyle C. Brady and Ray R. Weil Figure 7.22 (f)

©2002 Pearson Education, Inc. Upper Saddle River, New Jersey THE NATURE AND PROPERTIES OF SOILS, 13/e Nyle C. Brady and Ray R. Weil Soil Heating by Fire Fire breaks down the organic layer and recycles the nutrients into the soil Some seeds with hard coatings need to be heated above 70ºC before they will germinate (some pines) The heat from fire can kill some weed seeds Fire can cause the development of a hydrophobic layer

©2002 Pearson Education, Inc. Upper Saddle River, New Jersey THE NATURE AND PROPERTIES OF SOILS, 13/e Nyle C. Brady and Ray R. Weil Formation of a Hydrophobic Layer After Fire

©2002 Pearson Education, Inc. Upper Saddle River, New Jersey THE NATURE AND PROPERTIES OF SOILS, 13/e Nyle C. Brady and Ray R. Weil Heating by Solar Radiation On average only 50% of the solar radiation actually reaches the soil The majority of that energy goes to evaporating water or is reflected back into the atmosphere because of a high albedo Only about 10% of the solar radiation actually heats the soil

©2002 Pearson Education, Inc. Upper Saddle River, New Jersey THE NATURE AND PROPERTIES OF SOILS, 13/e Nyle C. Brady and Ray R. Weil Figure 7.26

©2002 Pearson Education, Inc. Upper Saddle River, New Jersey THE NATURE AND PROPERTIES OF SOILS, 13/e Nyle C. Brady and Ray R. Weil Figure 7.27

©2002 Pearson Education, Inc. Upper Saddle River, New Jersey THE NATURE AND PROPERTIES OF SOILS, 13/e Nyle C. Brady and Ray R. Weil Figure 7.31

©2002 Pearson Education, Inc. Upper Saddle River, New Jersey THE NATURE AND PROPERTIES OF SOILS, 13/e Nyle C. Brady and Ray R. Weil Figure 7.36

©2002 Pearson Education, Inc. Upper Saddle River, New Jersey THE NATURE AND PROPERTIES OF SOILS, 13/e Nyle C. Brady and Ray R. Weil