NRES 201 Lecture 23 Outline of Last Lecture I Ecological effects of soil aeration II Managing soil aeration III Wetlands and their soils Outline of Current Lecture IV Importance of soil temperature V Solar radiation and soil heating VI Thermal properties of soils VII Soil temperature control Current Lecture Importance of soil temperature Plant processes o Greater effect of soil than air temperature on shoot growth than root growth o Plants differ in soil temperature requirements o In the spring plant growth is often limited by cold soil temperatures But soil warming is not cost effective o In the summer high soil temperatures can be a problem Especially for a shallow rooted turfgrass o Soil temperatures trigger seed germination Species specific May require Temperature fluctuation Or previous exposure to cold 2 4 degrees C Vernalization o Cool soils slow root uptake of water and nutrients Can cause P deficiency Can also cause winter burn of evergreens if evaporative loss exceeds water uptake Microbial processes o Microbial activity is temperature dependent Some activity even below freezing Activity doubles with every 10 degree rise in soil temperature 35 40 degree C is optimal Freezing and Thawing These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute o Liquid water below the frost line is drawn toward ice lenses that continually expand in frozen soil o Enormous pressure cause frost heaving that lifts stones plants and fence posts And cracks foundations and roads o Thawing begins at soil surface o The melting ice contributes to surface runoff and erosion Soil heating by fire o Surface soil briefly heated by forest range or crop residue fires o Some mineral breakdown possible above 300 degrees C o Main effect is to destroy organic matter o Water infiltration is reduced And saturated soil above the water repellant zone can lead to mudslides Solar radiation and soil heating The solar radiation balance o Soils mainly heated by solar radiation o Only 50 of solar energy reaches the Earth Up to 75 in cloud free areas o Of the incident solar energy 90 evaporates water or is radiated back to the sky Only 10 heats the soil Albedo o Refers to the fraction of incident radiation that is reflected by the land surface o Depends on soil color and roughness o Dark soils are often cooler than light soils Because of a higher moisture content o Vegetation also affects albedo Aspect o The direction of slope o Greatest solar energy absorption when sunlight falls perpendicular to the soil surface o North facing slopes are moister and cooler o South facing slopes are drier and warmer Soil cover o Warming and cooling occur more quickly for bare soils than for those covered by Vegetation Mulch Or snow o The insulating effect of vegetation is due largely to transpiration
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