SOILSFORMATION, EROSION, AND

CONSERVATION

CHAPTER 10

I. Soil: Formation Erosion, and Conservation

A. Soil – Defined as a complex mixture of eroded rock, minerals, decaying organic matter, water,air , and living organisms.

1. Produced by…-Weathering of rock

-Depositing of sediment -Decomposition of matter

B. Soil Zones (MATURE)

-Mature Soil is arranged into zones called SOIL HORIZONS, each with distinct textures and compositions

-A cross-section of soil horizons is called a SOIL PROFILE

-Most mature soils have at least three of the possible horizons

LAYERS/HORIZONS

O Horizon – Top layer/Surface Liter Layer

-Characterized by debris and animal waste

-Dark Brown/Black in color

A Horizon – Top Soil Layer -Consists of porous mixture of partially

decomposed organic matter called HUMUS and *inorganic minerals -Generally darker and more loosely compact than lower levels.

-Most *plant roots and organic matter found here.

B Horizon – Subsoil Layer andC Horizon – Parent Material

-Contain most of soil’s inorganic matter and varying mixtures of sand, silt,clay, and gravel

-C Horizon lies on BEDROCK

Soils: Zones

O horizonLeaf litterA horizonTopsoil

B horizonSubsoilC horizonParent

material

Mature soil

Young soil

Regolith

Immature soil

Bedrock

-Spaces, pores, between particles contain varying amounts of water and air.

-Some of the precipitation that reaches the soils moves down through layers by a process known as… Infiltration- Water moving through the soil layers

-Leaching- Soil components from upper layers being carried to lower layers when water moves through soluble soil layers. Ex: dumping oil in yard

C. Soil Properties1. Soils vary in content of … Clay - very fine particle Silt – fine particles Sand – medium particles Gravel – coarse/very course

particles-Relative amounts of different size and types determines SOIL TEXTURE-LOAMS – soils of equal mixture….not a particle size used to determine soil texture.

2. Soil texture(s) can be determined by…A. Feel – Mixing a small sample of top soil and water, rub it between the fingers and thumb.

-Gritty = a lot of sand-Sticky = high amounts of

clay, rolls-Silt = smooth like flour-Loams = between the

extremesB. Use of “texture chart”

CLAY

SAND SILT

3. Soil texture helps to determine… - SOIL POROSITY, the measure of the volume of pores and distance of pores per volume of soil.

(important for water/air amounts)

-Porosity helps to determine SOIL PERMEABILITY, the rate at which water and air can move through soil.

Water Water

High permeability Low permeability

-Porosity also is influenced by SOIL STRUCTURE, the way that particles are organized.

Texture Nutrient Infiltration Water-Holding Aeration TilthCapacity Capacity

Clay Good Poor Good Poor Poor

Silt Medium Medium Medium Medium Medium

Sand Poor Good Poor Good Good

Loam Medium Medium Medium Medium Medium

Loams – best for cropsSands – easy to work but decrease waterClay – soils can easily become water-logged

-pH can be changed by adding LIME to acidic soils and SULFUR to those soils that are basic/alkaline

4. pH- Measure of alkalinity or acidity

II. Soil Erosion1. Defined as the movement of soil components, especially surface litter and topsoil, from one place to another*Two main agents are…

-Flowing water -Wind

2. Types Of Water Erosion A. Sheet – Moving of water in wide

flow

B. Rill – Fast moving water that cuts small channels

C. Gully – Ditches and gulleys caused by fast moving water over steep, exposed soil

Areas of serious concern

Areas of some concern

Stable or nonvegetative areas

Global Soil Erosion

3. U.S. Soil Erosion

-1/3 of the original top soil has been washed or blown away.

-USDA states that soil is eroding 16X faster than it can form.

-USDA estimated loss of $30 billion dollars in 1997

The Dust Bowl

A. Desertification- Process whereby the productive potential of arid or semiarid land falls by 10% or more due to human activities and climate changes. **Can be caused by prolonged drought, overgrazing, and soil compaction

B. Salinization-The accumulation of salts in soil -often a result of irrigation-stunts growth, decrease productivity, kills

plants making the land unproductive

4. Other Problems Associated With Soil

C. Waterlogging- An over abundance of water within the soil

-Often caused from trying to “wash out” salts.

-Occurs due to decrease drainage

-Irrigation often results in waterlogging

EvaporationTranspiration

Evaporation

Waterlogging

Less permeableclay layer

III. Soil Conservation

Soil Conservation involves reducing soil erosion and restoring soil fertility.

A. Farming Techniques 1.Conventional-tillage farming-plowing, breaking up, and smoothing soil in fall to plant in the spring. 2. Conservation-tillage farming-decreases erosion Tillage refers to the workability of soil

C. Terracing – Creation of broad, nearly level terraces that run across the contour of the lands

-Mostly used on very steep gradients to prevent erosion.

D. Contour Farming- Plowing/planting crops in rows across the sloped contour of the land at 90 degree angles.

E. Strip Cropping- Alternating rows of crops with low, ground hugging vegetation.

F. Alley Cropping/Agroforestry- several crops planted together in strips or alleys between trees or shrubs that are used for fuel wood or fruits.

G. Windbreaks/Shelterbelts- Rows of trees to reduce wind erosion.

H. Organic fertilizer

-Compost

-Animal manure-Green manure

Commercial inorganic fertilizer

Drawbacks to Commercial Inorganic Fertilizers

- They don’t add humus to soil- Show decreased ability to hold

water- Lower oxygen content in soil- Supply 2 or 3 of 20 needed

nutrients.