Soil Composition1/13/12

What determines characteristics of soil?

• Physical (such as water)• Parent material (chemical make-up)• Life (biological activity)• climate

What are the layers of soil? O Horizon - The top, organic

layer of soil, made up mostly of leaf litter and humus (decomposed organic matter).A Horizon - The layer called topsoil. Seeds germinate and plant roots grow in this dark-colored layer. It is made up of humus (decomposed organic matter) mixed with mineral particles.

E Horizon - This eluviation (leaching) layer is light in color; this layer is. It is made up mostly of sand and silt, having lost most of its minerals and clay as water drips through the soil (in the process of eluviation).B Horizon - subsoil contains clay and mineral deposits (like iron, aluminum oxides, and calcium carbonate) that it receives from layers above it when mineralized water drips from the soil above.C Horizon - regolith: consists of slightly broken-up bedrock. Plant roots do not penetrate into this layer; very little organic material is found in this layer.R Horizon - The unweathered rock (bedrock) layer.

What is soil fertility?

• The capacity of soil to supply nutrients necessary for plant growth.– Macronutrients:S, P, Mg, Ca, K, N, O, C, H– MicronutrientsCu, Zn, Mn, Fe

What role does decomposition play in nutrient cycling in soil?

• Decomposition provides nitrogen, phosphorus and carbon to the soil.

What is a limiting factor?

• The chemical/nutrient or material that may inhibit the fertility of the soil.– i.e. phosphorus

What is Liebig’s Law of the minimum?

• The idea that some single factor determines the growth and therefore the presence of a species.

What is the synergistic effect?

• Availability of one resource affects the response of an organism to some other resource. – i.e. increasing N to the plant increases phosphorus

uptake

N + P =

Does osmosis effect seeds?

• YES!• Osmosis = the passing of water across a

semipermeable membrane, to an area with a higher salt concentration.

Pros and Cons of Inorganic fertilizer? Advantages

• Easily obtained and transported

• Cheaper• Nutrients are

concentrated/less applied• Release specific minerals

Disadvantages• Adds no humus or organic

matter to soil/decreases water holding capacity

• Lowers oxygen content of soil and keeps nutrients from being taken up as efficiently

• Does not completely supply micronutrients

• Requires large amounts of E for production, transport and application

Advantages

• Nutrients immediately available

• Increase soil fertility• Increase crop yield• Speeds up the growing

process

Disadvantages

• Release nitrous oxide (N2O) a greenhouse gas

• Over application harms plants• Aquatic pollution resulting

from RUNOFF in surface or groundwater is detrimental to humans and ecosystems

• Organic fertilizers may be free if they can be obtained

Soil Composition 2

1/13/12

What are the soil textures? Table 1.

The Size of Sand, Silt and Clay

Name Particle Diameter

Clay below 0.002 millimeters

Silt 0.002 to 0.05 millimeters

Very fine sandFine sand

Medium sandCoarse sand

Very coarse sand

0.05 to 0.10 millimeters0.10 to 0.25 millimeters0.25 to 0.5 millimeters0.5 to 1.0 millimeters1.0 to 2.0 millimeters

Gravel 2.0 to 75.0 millimeters

Rock greater than 75.0 millimeters (~2")

What some chemical soil tests?

• pH• Salinity• Organic content• Ion Exchange

What do physical tests look for?

• Permeability• Porosity• Texture• Moisture content• Particle density• Soil

structure/clumping• Percolation rate

• Capillary of soil• Soil compaction• Soil profile Analysis• Color

What are the effects of grazing on soil?