What is true soil?

Question

What is true soil?

Answer 1

Soils are made up of four basic components: minerals, air, water, and organic matter. The minerals, rated by particle size, make up the texture but it requires all four components to create good structure for plants to grow in.

The minerals come from weathered or degraded rock. The parent rock material, climate, topography and organisms work together over time to create the various soil types. The mineral content of the underlying parent rock from which the soil was formed determines acidity or alkalinity of the soil. Clay, the smallest soil mineral particle, doesn't come from volcanic lava or quickly cooled igneous rock but sand does. Clay comes from magma, molten rock, that remains underground or very slowly cooled non-crystalline igneous rock. Silt is the mid-sized particle.

Balanced loams include all three of these types of particles in relatively equal amounts.

http://www.hort.purdue.edu/ext/loam.html

The bio-organic parts of soil, critical for good fertility, are ~85% humus from decomposed detritus, ~10% living plant roots, and ~5% edaphon, the biotic community.

The edaphon consists of microbes, fungi, bacteria, earthworms, micro/meso fauna, and macro fauna. Insects, earthworms, and other arthropods churn the soil and promote formation of soil structure, aeration, and nutrient cycling through degrading plant & animal detritus to produce humus.

The last two components, air and water, must be able to move freely though the soil. Once soil is compacted air and water are excluded destroying the healthy structure. Minerals represent less than half of the total soil volume, water and air occupy nearly 25% each, and organic matter the rest. Only in bogs or similar places does the organic portion go much higher.

These high organic contents occur in peat rich soils. The soil may be very acid, very wet in winter but dry in summer, and it may be fairly infertile due to the high pH. Unlike most other soil types peat rich soil is more than 20% organics so holds water like a sponge but can dry out totally in summer then it can be difficult to re-wet once it is dried out.