Soil – Notes & Focus

Force & Motion
Earth & Environment


Earth & Environment
Minerals – Notes & Focus
Minerals – Vocabulary
Minerals – Review
Minerals – Their Uses
Minerals – Lab Practical
Rocks – Notes & Focus
Rocks – Vocabulary
Rocks – Review
Rocks – ID Lab
Rocks – Lab Practical
Soil – Notes & Focus
Minerals – Review Sheet
“Panning for Gold” Lab

Soil Formation – Notes & Focus Questions

Directions: Read pp. 138 – 140 in the Heath Earth Science book, and pp. 295 – 297 in the Environmental Science book. Fill the names of the appropriate layers in the blanks provided.

  Soil is a mixture of organic matter and inorganic sediments. The organic content of soil comes from the decomposition of the predominant plant growth. The higher the organic content of soil, the richer it is. Deserts have little plant growth, and so have very little organic matter in their soils, and will continue to be unable to support much plant growth in the future. Forest soils vary. Coniferous forests drop Ό of their needles every spring and fall, and their decomposition makes the soil more acidic and better able to absorb and retain moisture than other forest soils. This is necessary, since they grow in areas that get less rainfall. Deciduous forests drop their leaves annually, but they can take two or three years to decompose, while new growth begins a few months later, so soils can be less rich. Rainforests support such a huge biomass that nearly all soil nutrients are tied up in living things, and surprisingly tend to have the poorest soils of all forests. Grasses decompose quickly, returning their nutrients to the soil readily, and are enriched by the manure of the herbivores that graze on them, yielding a high organic content. This makes them ideal for farmland. Climate affects soils too; the higher annual rainfall in forests tends to leach nutrients deeper into the soils, and the lower rainfalls in deserts and grasslands leaves the nutrients near the surface. The inorganic content of the soil is usually dependent on the parent rock it formed from. Oklahoma’s red soils come largely from the high iron content of the clays that form from the bedrock below, and our soils in this state tend to be “limey,” since 90% of the rock near the surface is limestone. Our grasses are adapted to it, and near urban areas, acidic rainfall (caused by air pollution) makes the addition of lime necessary to bring the soils back to the proper pH. Sometimes soils end up far from where they originally formed. Floodwaters erode topsoil from lands near their headwaters, where they are still flowing quickly, and deposit them in lands where they slow down, near their mouths. Loess is a type of soil that is moved by wind or glaciers to areas far from its parent rock, too.

A Horizon – Also called topsoil, this layer is found below the O horizon and above the E horizon. Seeds germinate here and plant roots grow in it.
B Horizon – Also called subsoil, or illuviation layer, this layer is below the E Horizon and above the C Horizon. It contains clay and minerals like iron and calcium carbonate that it receives from layers above it through leaching.
C Horizon – Also called regolith: the layer below the B Horizon and above the R Horizon. It consists of slightly broken-up bedrock.
E Horizon – Also called eluviation layer, this layer is below the A Horizon and above the B Horizon. It is mostly sand and silt, having lost most of its minerals and clay as water drips through the soil (in the process of leaching.)
O Horizon – Also called humus, the top layer of soil, made up mostly of partly decomposed leaf litter. This layer is present in dense forest soils, and may be absent in others.
R Horizon – Also called bedrock, the layer that is beneath all the other layers., the parent rock of the soil.

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