- Soil and its properties
- Soil profile
- Soil order
- Green plants and mycorrhizae


[SLIDE 1]

Soil consists of solid material of geological and biological origin that is changed by chemical, biological and physical processes to support plant life. As former President Franklin D Roosevelt said, "The nation that destroys its soil, destroys itself."

90% of the world's food supply comes from land-based agricultural systems. There are 4 textures of soil: sand, silt, clay and loam. Loam contains a mixture of 40% sand, 40% silt and 20% clay.

There are 5 properties of soil: water infiltration, water-holding capacity, nutrient-holding capacity, aeration, and workability, or the ease with which soil can be cultivated. Depending on the type of soil texture, there are different degrees to which water passes through, how much water and nutrients can be retained, how much air passes through the soil, and what types of plants can grow in that soil.


[SLIDE 2]

Soil Profile is a vertical slice through different layers or horizons of soil. Taking a soil profile reveals a lot about the soil composition and its formation.

There are 5 soil horizons:
- O horizon: humus containing surface litter and decomposing plant matter
- A horizon: topsoil containing mixed humus and leached mineral soil
- E horizon: zone of leaching containing less humus and minerals that resist leaching
- B horizon: subsoil containing leached minerals like iron and aluminum oxides
- C horizon: weathered parent material containing  broken-down minerals


[SLIDE 3]

One of the main methods of classification for soils is soil order. There are 12 major soil orders worldwide with 4 common soil orders that are important for agriculture, animal husbandry and forestry. They are mollisols, oxisols, alfisols and aridisols.

Mollisols are fertile, dark soils in temperate grasslands. This offers some of the best agricultural soil and is located in the midwestern US, Ukraine, Russia and Mongolia.

Oxisols are soils in tropical and subtropical rainforests. Alfisols are soils in moist, temperate forest biomes. Aridisols are soils in drylands and deserts.


[SLIDE 4]

Green plants protect soil from erosion and reduce water vapor loss. Keeping top soil is important for the health of plants. Soil deteriorates or is renewed through the loss or addition of organic matter.

Mycorrhizae are soil fungi that draw nourishment from the roots of plants. They also pull out nutrients from detritus or decaying matter in the soil and then transfer them to the plant.