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Physical properties – Texture Texture – proportions of sand, silt, and clay Determines water holding capacity, water availability, nutrient supply capacity.

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Presentation on theme: "Physical properties – Texture Texture – proportions of sand, silt, and clay Determines water holding capacity, water availability, nutrient supply capacity."— Presentation transcript:

1 Physical properties – Texture Texture – proportions of sand, silt, and clay Determines water holding capacity, water availability, nutrient supply capacity

2 Soil Texture Proportions of sand, silt, and clay Not OM – nonetheless important Not coarse fragments – nonetheless important

3 “Big”  smaller  really small Sand  silt  clay Relative Size Comparison of Soil Particles

4 The small arrows indicate the proper direction in which to draw the lines. Loam: Unequal proportions, Equal properties

5 Texture Surface area per unit volume –1 g sand ~ 0.1 m 2 –1 g silt ~ 1 m 2 –1 g clay ~ 10-1000 m 2 lowest highest Large surface area means more charge so greater ability to hold water and nutrients Coarse textured soils larger pores vs. fine textured soils greater total pore space (volume)

6 particle surface area pore volume nutrient supply capacity plasticity and cohesion swelling

7 pore size infiltration rate drainage rate aeration

8 Influence of Texture SandSiltClay Water-holding capacity Aeration Drainage Nutrient retention LowMediumHigh GoodPoor Medium SlowVery slowHigh LowMedium

9 Physical properties Density – Porosity – particle density: mass per unit volume (no air) bulk density: mass per unit volume (with air) Both: no water the volume percentage of the total bulk soil NOT occupied by solids

10 But soil properties greatly influenced by – Pore size range  Particle heterogeneity & Aggregation –Finer pores – water unavailable, poor aeration, little waterflow, –Finest pores – too small for microbes Pore network  Aggregation

11 Aggregation influenced by Coarse scale – biotic: –Roots, Burrowing animals (mammals, earthworms) –Sticky networks: root hairs, fungi Fine scale – physical/chemical: –Clay properties: Flocculation, bridging (multivalent cations) –Clay/humus/cation complexes –Cementing: Iron oxides (Ultisols & Oxisols) –Volume changes in clays: shrink/swelling, freeze drying


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