CH. 7 NOTES
CH. 7 NOTES PSS 3303
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This 5 page Class Notes was uploaded by Payton Gilmore on Tuesday October 4, 2016. The Class Notes belongs to PSS 3303 at Mississippi State University taught by Dr. Jac J. Varco in Fall 2016. Since its upload, it has received 5 views. For similar materials see Soils in plant and soil sciences at Mississippi State University.
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Date Created: 10/04/16
Chapter 7: Soil Aeration and T emperature Aeration (MACRO) Gas movement into and out of soil. Soil Atmosphere-variable from a standpoint of quantity and composition Degree of soil aeration influences plant, animal, and microbial growth as well as chemical oxidation-reduction. Most significant is the balance of CO2 and O2 Composition of soil air depends on moisture content, porosity, and root and microbial activity. Gases produced in the soil include CO2, NOx, H2S, NH3, and CH4. Atmosphere Soil atmosphere composition composition N2 78% 78% O2 21% 0 TO 20% (anaerobic to aerobic) CO2 0.0398% >0.0398 H2O Variable Near saturation Image on slide 6 Gas exchange Gas exchange between soil air and the atmosphere above it occurs by A. Mass flow - Barometric pressure changes - Wind - Fluctuations in soil moisture B.Diffusion: movement from high concentration to low - Majority of gas exchange in soils - Due to the partial pressure of the gas in question - Primarily O2 into soil and gases such as CO2 out of the soil. - CO2 diffusion through water is 10,000 x’s slower than it is through air - Replenishment of soil air depends on the O2 diffusion rate Aeration status affects: - Plant and mircrobial growth - Oxidation and reduction of chemical constituents. Aerobic vs. anaerobic 2- - SO 4 H2S - NO N 3 2 - Fe 3+ Fe 2+ - Mn 2+ Mn 4+ Factors influencing soil aeration and oxygen diffusion rate. - Porosity : TPS and PSD - Depth: CO2 and O2 o Greater CO2 deeper - Plant and Microbial activity: Temperature, availability of C substrates - Water content - Graph on slide 10 Temporal effects- Generally soil CO l2vels begin to rise in the spring and peak during mid-summer due to plant and microbial activity. 2 - As soil dries out, aeration towards end of summer becomes better. - Southern Hemisphere has less temporal effects - Nothern Hemisphere CO2 peaks around may and declines o Bc of more plants Soil Temperature Temperature effects on: - Chemical processes o Weathering rate o Nutrient availability - Biological processes o Microbial growth which influences OM decomposition and nutrient availability. o Plant growth, corn= 50* F, cotton=68*F, bermudagrass=75 to 80*F for best germination, seed dormancy, root growth/storage organs. Every plant has a certain temperature the soil must be to thrive When water evaporates from the soil it cools it Shortwave radiation during the day Longwave radiation going back to the atmosphere at night Soil warming is due to solar radiation absorption, soil cooling due to water evaporation, and re-radiation of heat to atmosphere - Image slide 14 - Greenhouse gases hold in heat 3 - Radiation hits greenhouse gases and reflects back Approximately 10% of solar radiation absorbed by soil Factors influencing absorption: 1. Angle of incidence (of sun) - Image slide 15 2. Albedo- degree of reflection of light by an object**** - The Higher the albedo the higher the reflection - White has the highest albedo (Snow) - Black absorbs the most - Different colors have different albedos - Water= 10% - snow=50% - Soil= 20% - Factors determining soil albedo include mulch cover and color, plant canopy, soil cover 3. Water content - Specific heat: o Soil= 0.2 cal/g/*C o H2O= 1.0 cal/g/*C - Soil texture- loamy sand vs. clay loam o Clay loam warms up slower o Sandy soil cools down quicker - NT vs. CT or residue no residue o No Tils o Residue holds more moisture o Bare soil cools down quicker than a mulch soil o A wet soils weighs a lot more than a dry soil 4 o The dry soil warms u quicker 4. Mulches - Residue quantity Insulating effect diurnal fluctuations o Mulch soils warms up slower o Doesn’t cool down as much at night - Solarization- heating of soil by the use of plastic mulches help to kill disease causing microbes 5. Depth- less temperature fluctuations w/ depth. - Graph slide 19 - Soil peaks around May, June,July - Shallow soil warms up most and fastest Soil Temperature Control 1. Mulches - Crop residues No Till vs Conventional Till - Landscaping mulches - Gravel or wood chips 2. Soil Modifications - Raised beds - Soil drainage 5
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