Soils Recapitulated (Lecture 9/15)

Soil: Soil is made up of minerals, water, air and living things. As a whole, it is a breathing, consuming, excreting, adapting, and ever changing ecosystem. Soil is approximately 20-30% water, 20-30% air, and 45% minerals, which come from rock.

Mineral: A mineral is a naturally occurring solid chemical substance that is formed through geological processes and that has a characteristic chemical composition, a highly ordered atomic structure, and specific physical properties. By comparison, a rock is an aggregate of minerals and does not have a specific chemical composition. A mineral can be composed of one or more different types of elements.

Element: A pure chemical substance consisting of one type of atom distinguished by it's atomic number, which is the number of protons in it's nucleus. All known elements are described on the Periodic Table of the Elements. Copper, a substance made up of only copper atoms, is an element, and it is also can be described as a mineral.

Ion: An atom or molecule that has lost or gained negatively charged electron(s) thereby posessing a positive or a negative charge. Examples include Na+, Cl-. NH4+.

What was Henry talking about when he said that "All elements up to Iron (Fe) are forged in the belly of stars."? Check out this video, it explains it really well.
http://www.youtube.com/watch?v=neMEo8ZrwuI

Soil Texture: Defined by how much and what proportions of each soil separate are present in a soil. For example, generally speaking, a soil with a large percent of sand could be described as sandy soil and would feel gritty when wet and would not hold water well. The texture of a soil cannot be changed. You can add more sand, or silt, or clay, to small areas, but you cannot change the overall soil texture. For more info:
http://nesoil.com/properties/texture/sld001.htm

Soil Separates: Sand, Silt, and Clay. See a diagram of the Soil Triangle at the link above for more detail.

Sand: Very large particles (0.05-2mm) chipped away from parent material (bedrock), quick to settle in water, very permeable (water drains through it quickly), warms up easily allowing for lots of growth in early spring, however loses heat quickly too and can get very cold at night. (compare it to a chair in size)

Silt: Size is intermediate to clay and sand (0.002-0.05 mm) or. Silt is created by glacial tailings or settling along river banks. Can kill soil by filling up pore spaces if in too high concentration, but can also cause problems if not present in large enough quantities. (compare it to a golf ball in size)

Clay: Tiny particles (< 0.002 mm) relative to silt and sand. Clay has an overall negative charge (it is often made up of negatively charged Si and Al ions), which attracts positively charged ions (such as H+, Ca+, Mg+, Na+, and K+) and causes them to adsorb on the surface of the clay particle. Clay holds water and nutrients well. It is not very permeable and settles out very slowly (hundreds of years). (compare it to a bee bee in size)

Soil Structure: Soil structure has to do with the physical arrangement of the soil particles. Soil structure is largely responsible for how a soil behaves and determines a farmer's or gardener's approach to working with it. A soil's structure may be described by the stability, size or shape of it's structural elements. For example "platy" is a description of the shape of a particular clay soil's structure. Soil structure can be changed by working the soil. Adding organic matter, sheet mulching, dust mulching, cover cropping and roto-tilling are some techniques used by farmers to improve soil structure for growing crops.

Soil Profile: A cross-section of soil revealing the different soil horizons, including the bedrock, C-Horizon, B-Horizon, A-Horizon and the O-Horizon.

Soil Fertility: Fertile soil has the following characteristics: It is rich in nutrients N, P, K, it contains sufficient trace elements (micronutrients) B, Cl, Co, Cu Fe, Mn, Mg, Mo, S and Zn. It contains organic matter and moisture, it's pH is in the range of 6-7, it has good soil structure (workable), it has good drainage, a range of microorganisms and plenty of topsoil.

Soil pH: The potential of free Hydrogen ions in solution.

Acidic Soil
If a soil is acidic, it has a low pH, between 0-7. Rhododendrons, Blueberries like acidic soils. In acidic soils, it is the macronutrients that are not as available for cation exchange at the root surface. Use limestone to amend acidic soil.

Alkaline Soil
If a soil is alkaline, it has a high pH, between 7-14. In alkaline soils, micronutrients are not absorbed as easily by the plant.

Neutral Soils
A pH of 7 is neutral. A pH of 6-7 is ideal for supporting life in the soil.

Cation: A positively charged ion.

Cation Exchange: The exchange of positively charged cations in the soil, for H+ ions at the root surface. Allows for the uptake of cationic nutrients by the plant roots.

Cation-Exchange Capacity (CEC): A measure of soil fertility. CEC is a measure of a soils ability to bind to cations (nutrients) and hold them for use by plants. The pH of a soil determines to a large extent the quantity of cation nutrients in the soil that are bound to clay particles, or that are free in the solution and available for cation exchange.

Acid: a compound (chemical/nutrient) that lets go of Hydrogen ions in solution. Carbonic Acid (H2C03) is an example.

Macronutrients: Nutrients necessary to plant life in large quantities: N, P, K, Ca, Mg, S

Micronutrients: Nutrients necessary to plant life in small quantities: Cl, Fe, Mn, Mo, Zn, Co, B, Cu, Zn.