SOIL PROPERTIES. 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:.
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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 • HeavySoils - clay or fine texture • LoamySoils - medium textured • more desirable characteristics usually associated with highly productive soils that are easier to manage
Light Soils vs Heavy Soils When 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-tillplanting - 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 Soil more 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 Structure Soil 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 Soil Animals • Micro • Nematodes • Protozoa • Macro • Earthworms • Rodents (prairie dogs, moles, gophers, etc.) • Arthropods (mites, insects, spiders, etc.) • Gastropods (slugs, snails, etc.)
Chemical Properties of Soil The 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) • Nitrogencycle – 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 • Acidsoil – one having a pH below 7.0 on a scale from 0 to 14 • Alkalinesoil – 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