General Soil Information

Definition of Soil Soil – relatively thin surface layer of the Earth’s crust consisting of mineral and organic matter that is affected by agents such as weather, wind, water, and organisms. Dynamic membrane that covers earth’s surface Connects biological and geological world

Ecosystem Services Provided by Soil

Importance of Soil Organisms, mainly microorganisms, inhabit the soil & depend on it for shelter, food & water. Plants anchor themselves into the soil, and get their nutrients and water. Terrestrial plants could not survive without soil, therefore, humans could not exist without soil either.

SOIL: A RENEWABLE RESOURCE Soil is a slowly renewed resource that provides most of the nutrients needed for plant growth and also helps purify water. Soil formation begins when bedrock is broken down by physical, chemical and biological processes called weathering. Mature soils, or soils that have developed over a long time are arranged in a series of horizontal layers called soil horizons.

Major Components of Soil Pore Space (50%) This may contain air and/or water Soil Space (50%) Organic Matter Mineral Matter

Soil Formation & Parent Material The rock that has slowly broken down into smaller particles by biological, chemical, and physical weathering. To form 2.5 cm (1 in.) it may take from 200-1000 years.

Soil Properties: Texture The percentages (by weight) of different sized particles of sand, silt and clay that it contains. For Example: a soil has 24% clay, 41% silt, and 35% sand. The soil is classified as: Medium loam

Texture Largest → Smallest Sand → Silt → Clay >2mm in diameter = gravel/stones (not actually considered soil because it doesn’t have direct value to plants. 0.05 to 2mm = sand (the largest soil particles) can be seen easily with the eye. 0.002 to 0.05mm = silt – about the size of flour and barely visible with the eye. <.002mm = clay (has the greatest surface value) – only seen under and electronic microscope.

Texture: The Ribbon Test To tell the difference in soil, take the soil, moisten it, and rub it between your fingers and thumb. Gritty -has a lot of sand Sticky- high clay content and you should be able to roll it into a clump Silt- smooth, like flour.

Physical Properties of Soils Texture: the amount of sand silt, and clay Structure: How soil particles are organized and clumped together. (Sand, silt, clay) Friability: How easily the soil can be crumbled Porosity: A measure of the volume of soil and the average distances between the spaces

Permeability The rate at which water and air moves from upper to lower soil layers. It is distances between those spaces. Why does soil need air spaces? Aerobic microorganisms need oxygen for cellular respiration! Can increase the water holding capacity of a soil by adding clay

Shrink-Swell Potential Some soils, like clays, swell when H2O gets in them, then they dry and crack. This is bad for house foundations, etc. Important for builders to know

C HOPKN’S CaFe Mg B Mn Cu Zn Cl Mo Soil Nutrients C HOPKN’S CaFe Mg B Mn Cu Zn Cl Mo Macronutrients: larger in atomic structure. Plants need them in large amounts Ex. Nitrogen, Phosphorus & Potassium. Micronutrients: smaller in atomic structure. Plants need them in small amounts. Ex. Selenium, Zinc & Iron

pH The pH of most soils ranges from 4.0 to 8.0. Plants are affected by pH because of the solubility of nutrient minerals. At a pH of 4.5, N, P, K, S, Ca, Mg are not very available to plants At a pH of 4.5, Fe, Mn, and Al are very available to plants and they are toxic to plants in high amounts Easy and inexpensive way to make an acidic soil more basic is to add crushed limestone (to fields) or egg shells to small gardens or house plants Inexpensive way to make Azalea beds more acidic is to add coffee grounds or pine needles or pine bark to the beds

Climate and Soils Probably the most important factor soils produced from the same parent material under different climates will have different properties Climate governs the rate and type of soil formation Main determinant of vegetation distribution. Soil climate has two major components; moisture (precipitation) and temperature, influencing evaporation. When precipitation exceeds evaporation, leaching of the soil will occur. Temperature determines the rate of reactions: Chemical and biological decay Influences weathering of soil

Soil Horizons A horizon B horizon C horizon

Soil Horizons O: Organic Horizons Organic Layers of Decaying Plant and Animal Tissue (detritus) Aids Soil Structural Development Helps to Retain Moisture Enriches Soil with nutrients as the leaf litter decomposes O Horizon Desert soils do not have O horizon; no leaf litter Dark in Color Because of Humus Material - 1,000,000 bacteria per cm3

Soil Horizons: A Horizon or “ Topsoil” It is dark and rich in accumulated organic matter and humus. It has a granular texture and is somewhat nutrient-poor due to the loss of many nutrient minerals to deeper layers and by leaching. Humus: A dark-brown or black organic substance made up of decayed plant or animal matter. A Horizon Grasslands and forests have deep A horizons (lots of humus which increases water holding capacity

Soil Horizons: E Horizons Mineral Horizon Near Surface Movement of Silicate Clay, Iron, and Aluminum from the A Horizon through Eluviation Eluviation: movement of materials suspended through a soil Horizon does not mean a water table is present, but the horizon can be associated with high water table E Horizon

Soil Horizons: B Horizons Zone of Maximum Accumulation The light-colored subsoil beneath the A-horizon often a zone of illuviation where nutrient minerals have leached out of the topsoil and litter accumulate Typically rich in iron and aluminum compounds and clay. B Horizon

Parent Material (C-horizon) Contains weathered pieces of rock & borders the un-weathered solid parent material. Most roots do not go down this deep and it is often saturated with groundwater.

Layers in Mature Soils Infiltration: the downward movement of water through soil. Leaching: dissolving of minerals and organic matter in upper layers carrying them to lower layers. The soil type determines the degree of infiltration and leaching.

Fertilizers and Labels N – P – K 12 – 3 - 10 Organic Fertilizers – animal manure, crop residues, bone meal, and compost Inorganic Fertilizers – man-made from chemical compounds Benefits – exact compositions are known; they are soluble & thus immediately available to the plant Costs – quickly leach away; this pollutes the water; doesn’t help the water holding capacity of the soil like organic fertilizers do