SOIL PROPERTIES

Unit Four: Soil ScienceAgriscience I

OBJECTIVES Describe soil by physical, chemical, and

biological properties of the soil.

Distinguish among physical, chemical, and biological properties of the soil.

Distinguish between homogenous and heterogeneous mixtures in soil.

Objective 1: TERMS TO KNOW:

Clay- The smallest soil particle Sand - The largest soil particle Silt - An intermediate sized soil particle Structure - The way individual soil

particles are grouped together Texture - A physical property of the soil

referring to the relative percentages of sand, silt, and clay

Objective 1: TERMS TO KNOW: (Cont’d) Topsoil - The upper part of the soil profile that is

normally cultivated Subsoil - the area in the soil profile below the

topsoil which accumulates clay Subsoiling - A method of breaking up the compacted

layers of the soil that restrict air and water movement and root growth using farm machinery

Tillage pan - areas of compacted soil in the plant root zone created by repeated plowing of heavy soils especially when wet; also called a plow pan

Mottling - Spots of color in the soil that indicates internal drainage and aeration

Texture physical property of soil considered rather

permanent refers to the relative percentages of the

three types of soil particles Sand Silt Clay

Determining Soil Texture Sensing the feel

It is the varying amount of each soil particle type that gives soil its texture or feel.

Mechanical analysis

Textural Triangle used to obtain a soil

textural name for a sample after it has been mechanically analyzed

Light Soils vs Heavy Soils Light Soils - sandy or coarse texture Heavy Soils - clay or fine texture Loamy Soils - medium textured

more desirable characteristics usually associated with highly productive soils that are easier to manage

Light Soils vs Heavy SoilsWhen comparing light soils to heavy soils,

the light soil will: require less energy to cultivate heat and cool faster usually lighter in color wet and dry faster usually subject to greater erosion usually lower in fertility

Four Main Types of Soil Structure Platy - thin horizontal sheets overlapping

each other Prismatic - long vertical columns without

rounded tops Block-like - irregular shaped cubes Spheroidal - rounded and often referred

to as granular or crumb; usually found in the topsoil

Two Types of Structureless Soils Single grained soils like sand

Solid massive condition with no noticeable peds

Internal Soil Drainage important for proper plant growth Permeability can be determined by the color of

the subsoil. Grey with some red or yellow streaks - poorly

drained soils Yellowish-brown or reddish brown with

some grey mottling - as internal drainage improves

Uniform bright color with few or no grey streaks or mottling – good internal drainage and aeration

Objective 2: TERMS TO KNOW: Infiltration - The movement of water

into the soil Percolation - The movement of water

through the soil No-till planting - The planting of a crop

into the previous crop stubble or a cover crop, disturbing only the immediate seed zone

Objective 2: TERMS TO KNOW: (Cont’d)

Reduced-tillage - The elimination of one or more operational procedures from

a conventional system of working the soil

Permeability - the characteristics of a soil which permits variations in the speed of air and water movement

Soil Types Influence Crop Selection Light textured soil

Oats peanuts beets

Loamy textured soil majority of Louisiana crops grow best in a loamy

textured soil. Heavy textured soil

Flooded rice requires a heavy fine textured soil to prevent loss of

surface water Sugarcane

Determination of Soil Structure determined by the way the particles of

sand, silt, and clay are grouped together in aggregates

Peds - naturally formed groups of soil particles

Clods - are artificially formed groups of soil particles

Structured Soilmore desirable because it: is easier to cultivate allows more water intake does not restrict root growth encourages better drainage within pore

spaces allows entry of oxygen into the pore

spaces after the water has drained facilitates organic matter decomposition

and the release of plant nutrients

Destruction of Soil StructureSoil structure can be destroyed by: working the soil when it is wet

repeated movement of equipment or livestock

repeated use of equipment at the same depth in the soil

continual flooding of the soil

Improving Soil Structure Leaving it alone, in time it will repair itself

Planting a green manure crop

Incorporating plant residue into the soil

Infiltration and Percolation Rates Rapid - spheroidal structure and single

grained structure less soils

Moderate - blocky and prismatic structure

Slow - platy structure or massive structure less soil

Tillage Pans and Traffic Pans Tillage pans - areas of compacted soil in

the plant root zone caused by repeated plowing at the same depth.

Tillage and traffic pans are serious problems in many parts of the country because the area of root restriction is generally in the topsoil. reduces the movement of air, water, and roots

and therefore limits crop yields.

Fragipans Fragipans (silt pans) and clay pans can

occur naturally in or near the subsoil. A fragipan is the result of too much silt in or near the B horizon, and is not the result of mans actions.

Alleviating Traffic or Tillage Pans Subsoiling breaks up or shatters

compacted layers using deep plowing equipment.

Reduced or minimum tillage means less movement over the soil which results in less compaction of the soil. Deep Subsoiling should precede reduced or minimum till operations.

No till reduces the formation of traffic pans because planting is done directly in the stubble of the previous crop.

Biological Properties of Soil refers to the living organisms found in the

soil includes both the micro and macro plants

and animals.

Plants Micro

Bacteria Fungi Actinomycetes

Macro – roots of higher plants

Biological Properties of SoilAnimals

Micro Nematodes Protozoa

Macro Earthworms Rodents (prairie dogs, moles, gophers, etc.) Arthropods (mites, insects, spiders, etc.) Gastropods (slugs, snails, etc.)

Biological Properties of Soil – Food Web

Chemical Properties of SoilThe ability of soil to provide the essential elements needed for plant growth includes:

the availability of these elements other chemical properties

clay minerals present humus content cation exchange soil reaction (pH).

Objective 3: TERMS TO KNOW: Homogenous mixtures – soil mixtures that

contain the same type of soil particles Heterogeneous mixtures – soil mixtures that

contain different types of soil particles

Aerobic – occurring only in the presence of free oxygen

Algae – soil plant microorganisms capable of photosynthesis

Anaerobic – growing or occurring in the absence of free oxygen

Objective 3: TERMS TO KNOW: (cont’d) Bacteria – single-celled soil plant

microorganisms, some of which are responsible for organic matter decomposition, while others are responsible for nitrogen fixation

Fungi – soil plant microorganisms responsible for organic matter decomposition, especially the cellulose, lignin and gum

Microorganisms – life forms too small to be seen with the unaided eye or barely visible

Nematodes - soil animal microorganisms that are responsible for the decomposition of organic mater, consumption of other animal microorganisms and parasitism on the roots of certain higher plants

Objective 3: TERMS TO KNOW: (cont’d) Nitrogen cycle – the biochemical changes undergone by

this atmospheric gas from its use by living organisms to decomposition and conversion back to the atmosphere

Organic matter – soil materials including plant and animal residues at various stages of decomposition

Rodents – small gnawing animals such as rats and mice Acid soil – one having a pH below 7.0 on a scale from 0 to

14 Alkaline soil – one having a pH below 7.0 on a scale from

0 to 14 Ion – charged atoms or groups of charged atoms pH – a numerical measure of the degree of acidity or

alkalinity of the soil solution

Homogenous Soil Mixtures Sand Silt Clay

Heterogeneous Soil Mixtures Any combination and proportion of

sand, silt, or clay