Soil Structure Types & Development PDF

R.W. Dirszowsky – Lecture Notes (Fall 2024) Page 21 Soil Structure Types Platy relatively thin, horizontal, plat...

R.W. Dirszowsky – Lecture Notes (Fall 2024) Page 21 Soil Structure Types Platy relatively thin, horizontal, plates, leaflets, or lenses found in all horizons typically inherited from parent material Block-like irregular six-sided forms (sides with more or less equal dimensions) sub-types include blocky or sub-angular normally found in B horizons Prism-like vertically oriented columns of soil up to 15 cm long sub-types include columnar and prismatic normally found in B horizons Development of Soil Structure Soil aggregation generally regarded as a two step process of aggregate formation and aggregate stabilization generally aggregates are formed where soils are subject to: shrinking and swelling freezing and thawing plant root penetration a stable soil is able to resist processes such as compaction or sudden wetting disintegration of aggregates by rapid wetting is called “slaking” Aggregate formation is considered in terms of two size groups microaggregates (< 250 µm) macroaggregates (> 250 µm) aggregates larger than 1cm are referred to as “clods” ENV1011 – Soil Science Cambrian College - Environmental Technician R.W. Dirszowsky – Lecture Notes (Fall 2024) Page 22 Formation of Microaggregates Microaggregate formation begins when microscopic clay minerals are stacked together into “domains” flocculation versus deflocculation strongly controlled by the presence of ions with more than one charge single-charge ions (e.g. Na+, K+) tend to neutralize the surface of the clay particles excess charges (e.g. Ca2+, Mg2+, Al3+) provide attraction to adjacent particles once formed domains may be grouped together and stabilized by interactions with organic matter organic matter associated with clay minerals is resistant to microbial decomposition referred to as “persistent” organic matter Formation of Macroaggregates Once formed microaggregates can coalesce into larger aggregates or macroaggregates referred to as the “aggregate hierarchy model” again primarily bound by organic matter tending to produce multiple macroaggregates rather than a continuous massive block of soil Two categories of organic matter in this case temporary stabilizing agents microbial and plant byproducts long chain polysaccharides transient stabilizing agents fine plant roots and fungal hyphae ENV1011 – Soil Science Cambrian College - Environmental Technician