1 Unit Four: Soil Science Agriscience I SOIL PROPERTIESUnit Four: Soil ScienceAgriscience I
2 OBJECTIVESDescribe 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.
3 Objective 1: TERMS TO KNOW: Clay- The smallest soil particleSand - The largest soil particleSilt - An intermediate sized soil particleStructure - The way individual soil particles are grouped togetherTexture - A physical property of the soil referring to the relative percentages of sand, silt, and clay
4 Objective 1: TERMS TO KNOW: (Cont’d) Topsoil - The upper part of the soil profile that is normally cultivatedSubsoil - the area in the soil profile below the topsoil which accumulates claySubsoiling - A method of breaking up the compacted layers of the soil that restrict air and water movement and root growth using farm machineryTillage pan - areas of compacted soil in the plant root zone created by repeated plowing of heavy soils especially when wet; also called a plow panMottling - Spots of color in the soil that indicates internal drainage and aeration
5 Texture physical property of soil considered rather permanent refers to the relative percentages of the three types of soil particlesSandSiltClay
6 Determining Soil Texture Sensing the feelIt is the varying amount of each soil particle type that gives soil its texture or feel.Mechanical analysis
7 Textural Triangleused to obtain a soil textural name for a sample after it has been mechanically analyzed
8 Light Soils vs Heavy Soils Light Soils - sandy or coarse textureHeavy Soils - clay or fine textureLoamy Soils - medium texturedmore desirable characteristics usually associated with highly productive soils that are easier to manage
9 Light Soils vs Heavy Soils When comparing light soils to heavy soils, the light soil will:require less energy to cultivateheat and cool fasterusually lighter in colorwet and dry fasterusually subject to greater erosionusually lower in fertility
10 Four Main Types of Soil Structure Platy - thin horizontal sheets overlapping each otherPrismatic - long vertical columns without rounded topsBlock-like - irregular shaped cubesSpheroidal - rounded and often referred to as granular or crumb; usually found in the topsoil
11 Two Types of Structureless Soils Single grained soils like sandSolid massive condition with no noticeable peds
12 Internal Soil Drainage important for proper plant growthPermeability can be determined by the color of the subsoil.Grey with some red or yellow streaks - poorly drained soilsYellowish-brown or reddish brown with some grey mottling - as internal drainage improvesUniform bright color with few or no grey streaks or mottling – good internal drainage and aeration
13 Objective 2: TERMS TO KNOW: Infiltration - The movement of water into the soilPercolation - The movement of water through the soilNo-till planting - The planting of a crop into the previous crop stubble or a cover crop, disturbing only the immediate seed zone
14 Objective 2: TERMS TO KNOW: (Cont’d) Reduced-tillage - The elimination of one or more operational procedures from a conventional system of working the soilPermeability - the characteristics of a soil which permits variations in the speed of air and water movement
15 Soil Types Influence Crop Selection Light textured soilOatspeanutsbeetsLoamy textured soilmajority of Louisiana crops grow best in a loamy textured soil.Heavy textured soilFlooded ricerequires a heavy fine textured soil to prevent loss of surface waterSugarcane
16 Determination of Soil Structure determined by the way the particles of sand, silt, and clay are grouped together in aggregatesPeds - naturally formed groups of soil particlesClods - are artificially formed groups of soil particles
17 Structured Soil more desirable because it: is easier to cultivate allows more water intakedoes not restrict root growthencourages better drainage within pore spacesallows entry of oxygen into the pore spaces after the water has drainedfacilitates organic matter decomposition and the release of plant nutrients
18 Destruction of Soil Structure Soil structure can be destroyed by:working the soil when it is wetrepeated movement of equipment or livestockrepeated use of equipment at the same depth in the soilcontinual flooding of the soil
19 Improving Soil Structure Leaving it alone, in time it will repair itselfPlanting a green manure cropIncorporating plant residue into the soil
20 Infiltration and Percolation Rates Rapid - spheroidal structure and single grained structure less soilsModerate - blocky and prismatic structureSlow - platy structure or massive structure less soil
21 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.
22 FragipansFragipans (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.
23 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.
24 Biological Properties of Soil refers to the living organisms found in the soilincludes both the micro and macro plants and animals.PlantsMicroBacteriaFungiActinomycetesMacro – roots of higher plants
27 Chemical Properties of Soil The ability of soil to provide the essential elements needed for plant growth includes:the availability of these elementsother chemical propertiesclay minerals presenthumus contentcation exchangesoil reaction (pH).
28 Objective 3: TERMS TO KNOW: Homogenous mixtures – soil mixtures that contain the same type of soil particlesHeterogeneous mixtures – soil mixtures that contain different types of soil particlesAerobic – occurring only in the presence of free oxygenAlgae – soil plant microorganisms capable of photosynthesisAnaerobic – growing or occurring in the absence of free oxygen
29 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 fixationFungi – soil plant microorganisms responsible for organic matter decomposition, especially the cellulose, lignin and gumMicroorganisms – life forms too small to be seen with the unaided eye or barely visibleNematodes - 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
30 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 atmosphereOrganic matter – soil materials including plant and animal residues at various stages of decompositionRodents – small gnawing animals such as rats and miceAcid soil – one having a pH below 7.0 on a scale from 0 to 14Alkaline soil – one having a pH below 7.0 on a scale from 0 to 14Ion – charged atoms or groups of charged atomspH – a numerical measure of the degree of acidity or alkalinity of the soil solution