NRES 201 Lecture 13 Outline of Last Lecture I Review of Previous Coverage II Revisiting Texture III Soil Density Outline of Current Lecture IV Soil Management and Bulk Density V Soil Porosity VI Aggregate formation and stabilization Current Lecture Soil management and bulk density Forest lands Db for undisturbed surface soils typically 1 2 g cm 3 Soil compaction can occur from Timber harvest and recreation pressure Adverse consequences include Slower tree growth increased runof Urban soils Soil compaction a common problem for urban tree plantings Useful practices to enhance root growth o Dig an oversized hole backfill with loose soil Green roofs Db a critical factor for design Two options for minimizing mass Limit soil depth by growing turfgrass Agricultural land Tillage temporarily decreases Db o But the long term efect is to increase Db because of organic matter depletion and weaker soil structure Short term changes in Db vary with the type of tillage High Db impedes root growth o The impedance arises from High soil strength resistance to deformation as measured with a penetrometer Poor aeration Slow movement of nutrients and water Buildup of toxic gases and root exudates 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 Soil strength increases with Db and decreases with higher soil water content Soil strength also depends on soil texture o At a given Db resistance to root penetration to increase with clay content To reduce soil compaction Minimize wheel traffic Increase tire width stay of wet soils Soil porosity Calculation of percent pore space o pore space 100 Db Dp 100 Range of soil porosity From 25 in compacted subsoils to 60 in well aggregated organic rich surface soils Size of soil pores o Macropores Larger than 0 08 mm Packing pores interped pores biopores o Micropores Smaller than 0 08 mm Some are too small for root hairs or microorganisms Usually filled with water Cultivation and soil porosity o Continuous cropping leads to the loss of soil organic mater o The consequences include Lower total porosity Lower macroporosity Higher microporosity Higher bulk density Tillage Short term benefits if the soil is not to wet or too dry o For loosening the surface soil o For breaking clods o For preparing a good seedbed Long term efect is to weaken soil aggregates o Organic matter is depleted by greater microbial activity
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