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: 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 Subsoil - the area in the soil profile below the Subsoiling - A method of breaking up the compacted Tillage pan - areas of compacted soil in the plant Mottling - Spots of color in the soil that indicates normally cultivated topsoil which accumulates clay layers of the soil that restrict air and water movement and root growth using farm machinery zone created by repeated plowing of heavy soils especially when wet; also called a plow pan internal drainage and aeration root 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 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-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 Loamy textured soil Oats peanuts beets 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.) Biological Properties of Soil – Food Web 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) 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
