Ms. Lacross April 2015 Agriscience and Technology I Introduction to Soil Science.
SOIL PROPERTIES Unit Four: Soil Science Agriscience I.
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Transcript of SOIL PROPERTIES Unit Four: Soil Science Agriscience I.
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