NRES 201 Lecture 13 Outline of Last Lecture I. Review of Previous CoverageII. Revisiting TextureIII. Soil DensityOutline of Current Lecture IV. Soil Management and Bulk DensityV. Soil PorosityVI. Aggregate formation and stabilization Current LectureSoil 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 runofUrban soils:- Soil compaction a common problem for urban tree plantings- Useful practices to enhance root growth:o Dig an oversized hole - backfill with loose soilGreen roofs:- Db a critical factor for design- Two options for minimizing mass: Limit soil depth by growing turfgrassAgricultural land:- Tillage temporarily decreases Dbo 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 growtho 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 exudatesThese 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 textureo 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 soilsSoil 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, bioporeso 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 matero 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 soilo For breaking clodso For preparing a good seedbed- Long - term efect is to weaken soil aggregateso Organic matter is depleted by greater microbial
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