Soil: Not just a four letter word!

What is soil? Soil is a mixture of minerals, organic matter, gases, liquids, and organisms that together support life.

What is soil? Soil Subsoil Living soil is the top layer with organic material and biota, while subsoils are inorganic and generally will not sustain plant life.

The primary components are clay, silt, and sand. The mineral part .002- The mineral part of soil comes in many forms and textures, dependent on parent material and geologic history. The primary components are clay, silt, and sand.

The mineral part: Clay Clay Forms “ribbon” Particles plate-shaped, <2 μm Retains water Adsorption – Clay particles hold a lot of water on their surfaces but don’t let it go. Clay is formed by chemical weathering of rock over millennia.

The mineral part: Silt Silt Stains fingers, short ribbons Particles irregular, 2-50 μm Retains nutrients Silt is formed by chemical and physical weathering of sand and is frequently transported by water. It often has very fine organic material mixed in.

The mineral part: Sand Sand Does not ribbon Particles angular, 50-2000 μm Provides drainage but has poor nutrient retention Mostly formed of silica quartz eroded by water or ice (glaciers), often from granite when the feldspar dissolves leaving quartz crystals.

Loam is the “sweet spot”, about 40% sand, 40% silt, and 20% clay.

Loam is the “sweet spot”, about 40% sand, 40% silt, and 20% clay.

Soil structure Porocity – Soils have micropores (space between particles) and macropores (worm tunnels, roots) that affect water flow.

The carbon cycle Soil should be thought of as a process, not just a material. Organic material is continually introduced, decomposed, and transformed.

Contributors to organic soil The organic material in soil retains water and nutrients, and provides coarse texture that supports air pockets. Sources include roots, fungi, litter/thatch, and many organisms.

“The little bugs have littler bugs” Millipedes, sowbugs, & beetles eat larger chunks, poop smaller chunks. Earthworms, nematodes, & mites eat those, poop smaller chunks yet. Tardigrades, soil fungi, & bacteria eat those, poop microscopic material that can be taken up by plants. Molds and other fungi can tackle all sizes! Organic material is broken down in size by a succession of organisms, each eating the debris left by larger critters. These organisms are collectively called “detritivores”.

The nitrogen cycle Soil nitrogen comes from N-fixing plants, lichens, and animal turnover and “by products”

The nitrogen cycle Soil nitrogen comes from N-fixing plants, lichens, “Foliose” Lichens Lobaria Alders Legumes (vetch) Peltigera Soil nitrogen comes from N-fixing plants, lichens, and animal turnover and “by products”

Soil nutrients & pH Nitrogen (N): Necessary for photosynthesis - Constituent of chlorophyll and amino acids Phosphorus (P): Necessary for metabolism, flower formation - ATP, RNA, areas of rapid cell division (meristems) Potassium (K): Necessary for metabolism - Osmotic regulation, eg. stomatal control Micronutrients: Bo, Cl, Cu, Fe, Mn, Mb, Zn - Needed in miniscule quantities for cellular metabolism, N fixing Soil pH: Acidity - 7.0 is neutral, 5-6 acidic, 8-9 alkaline - Range is 0-14, wet climates generally have acidic soils and dry climates generally have alkaline soils - Add lime to increase pH, ammonium sulfate to decrease pH

Questions?