Soil is. Pieces of rock Minerals Decaying organic matter Water Air Living organisms All mixed together!

Soil is. Pieces of rock Minerals Decaying organic matter Water Air Living organisms All mixed together!

Soil Horizons the layers of soil O-horizon: the surface litter. Mainly black or brown A-horizon: the top soil layer. Made out of humus. Both of these layers have abundant living organisms and root systems.

Soil Horizons B-horizon: the subsoil. More rock and less humus. C-horizon: the parent material. Bedrock.

Soil Renewable or nonrenewable? Varies in content of Clay very fine particles, low permeability, high water retention, feels sticky when wet, very little air or nutrients. Silt fine particles, good permeability, good water retention, feels gritty, good amount of air and nutrients. Sand large particles, fast permeability, low water retention, large amount of air. Very little nutrients. Loam equal amounts of silt and sand with a little less of clay. Ideal for living organisms.

Soil types

Soil Nutrient Cycle: Nutrients are continually cycled from soil to organisms and back to the soil. What factors are affecting the nutrient cycle?

Humus black or dark brown organic material that remains after decomposition. Increases the water holding capacity and binds nutrient mineral ions.

Pore space roughly 50% of the soil s volume is space. This space is filled with varying proportions of soil water and soil air. Both are necessary for optimal soil. Soil water is generally held in the smaller pores while soil air is held in the larger pores. The soil water contains low concentrations of dissolved nutrient minerals.

If the soil water is not bound to the soil particles or absorbed by roots, it continues to percolate downward through the soil, carrying the dissolved nutrients minerals with it. This is called leaching.

The deposition of leached material in the lower layers of soil is known as illuviation. Humus, clay, iron and aluminum compounds are some materials that can leach into the lower horizons of the soil. Some soils have an E horizon (sandwiched between the A and B) that is heavily leached Some substances completely leach out of the soil because they are soluble in water.

Soil air contains the same gases as the atmosphere but in different proportions. Usually more CO2 compared to O2 Most important are O2 for the soil organisms, N2 for nitrogen-fixing bacteria, and CO2 for weathering.

Soil organisms are most numerous in the O and A horizons. Include millions of microorganisms like bacteria, fungi, algae, microscopic worms (nematodes) and protozoa. Other organisms include plant roots, arthropods (insects, spiders, millipedes etc ), earthworms, moles, snakes, and ground hogs.

Soil organisms provide many essential services: Cycling organic material Prevent soil erosion Breakdown toxic materials Cleanse soil water Cycling atmospheric gases

Soil Texture Reading a soil textural triangle.

The largest soil particles are called, medium soil particles are called, and small soil particles are called. Which particle has the greatest surface area to volume ratio? Clay which mainly has a negative charge to it s surface. This is important because most soil minerals carry a positive charge. (K+ or Mg 2 +)

Many of the positively charged mineral ions get held in the soil by their interactions with clay. Most of the negatively charged minerals are not held as tightly and tend to leach out of the soil horizon or the soil altogether. Soil ph optimum range for plant growth is from 6.0 to 7.0 because most plant nutrients are available in this ph range.

In acidic soils, some important plant minerals are unable to bind to the soil. What often happens as a result? They are leached out. A lower ph can also make some elements more soluble in water, like Al and Mn, which are toxic to plants in higher concentrations, and some elements, like calcium phosphate, less soluble in water and less available for plants.

Major Soil Groups Due to variations in climate, local vegetation, parent material, geology, topography, and soil age throughout the world, there are thousands of soil types. There are 17,000 different soil types in the United States alone. Let s focus on five soil types that are very common:

Regions with colder climates, ample precipitation, and good drainage typically have soils called spodosols. Spodosols usually form under coniferous forests and have a layer of acidic needle litter, an acidic, ash-gray E horizon, and a darker brown B horizon. Does not make good farmland.

Temperate deciduous forests grow on alfisols. The A horizon is brown to gray-brown. There is enough precipitation to wash the clay and nutrients out of the A and E horizons. This is great soil if the forest is left intact. If cleared for farming, it needs to have fertilizers to maintain fertility.

Mollisols are very fertile soils found in temperate, semiarid grasslands. They have a thick, dark brown to black A horizon. Most of the world s grain crops are grown on mollisols.

Aridisols are found in arid regions. The lack of precipitation in these deserts limits leaching and the lack of vegetation limits amount of organic matter. Tend to have a thin A horizon. Accumulation of salts in the B horizon.

Oxisols are low in nutrient minerals and are found in tropical or subtropical areas with ample precipitation. Very little surface litter due to rapid decomposition. A horizon rich with humus but acidic. Thick B horizon is highly leached and nutrient poor.

Let s try to identify the following soil profiles: 1.? alfisol 2.? mollisol 3.? aridisol 4.? oxisol

Soil Problems the major problems are soil erosion and mineral depletion Can occur naturally. How? Accelerated or exacerbated by human activities. Which could be? Erosion is the wearing away or removal of soil from the land.

Mineral depletion all the essential nutrients cycle between the soil and organisms found in the soil. (mainly plants.)