410 likes | 860 Views
SOILS. Excerpts of the presentations of: Basic Soil Science &The Soil Resource Web Pages http://www.soils.agri.umn.edu/academics/classes/soil2125/. SOIL i –.
E N D
SOILS Excerpts of the presentations of: Basic Soil Science&The Soil Resource Web Pages http://www.soils.agri.umn.edu/academics/classes/soil2125/
SOIL i – • SOIL - The unconsolidated mineral or organic material on the immediate surface of the earth that serves as a natural medium for the growth of land plants.
Soil ii • The unconsolidated mineral or organic matter on the surface of the earth that has been subjected to and shows effects of genetic and environmental factors of:
Factors • 1) climate (including water and temperature effect • 2) macro- and microorganisms, conditioned by • 3) relief, acting on • 4) parent material over a period of • 5) time.
Soil – A Product • soil differs from the material from which it is derived (Parent Material) in many : • a) physical, • b) chemical, • c) biological, and • d) morphological properties and characteristics.
Soils are Dynamic • the % air, % water, % organic matter will change with time and space. • The Soil Ecosystem = all parts of the soil, including biotic and abiotic.
Soils and Plant Growth • Physical support of plants • Provides water and air • Provides essential elements • Macro-nutrients = N,P,K,Ca,Mg,S • Micro-nutrients = B,Fe,Mn,Cu,Zn,Mo,Co,Cl
Organic Horizons • O - horizon - organic material (no mineral materials) 1) forest litter 2) organic soil or peat soils, or muck • Oi - undecomposed (fibris) • Oe - moderate decomp. (hemis) • Oa - decomposed (sapric)
Processes of Mineral Soil Horizon Formation • A. Additions - H2O, organic matter,air, soil particles, salt • B. Losses - H2O, organic matter, CO2 , nutrients by plant removal • C. Transformations - Changes to soil structure, development of clay minerals, weathering of minerals to elements, chemical Rx • D. Translocations - movement from one horizon to another of O.M. Clay, Water, Iron, & Nutrients in colloidal size, (very small particles)
Mineral Soil Horizons • A horizon - surface horizons that accumulate O.M. • Ap = plowed soil Ap EB Bt BC C
E Horizons • E - (formerly A2) - Translocation out - Zone of Eluviations - Leaching out • lighter in color than horizons above or below A E E/B Bt BC C
B Horizons-two kinds: • a) Translocation in - below an A, E, or O with an accumulation of clay, iron, humus (O.M. decomposed) or carbonates (CaCO3) • b) or alteration of the original parent material, development of color or structure Bt
C Horizons • C - little affected by pedogenic processes and lack properties of O-A-B-E- or is the Parent Material • R = hard rock Solum A + B C horizon
Soil Texture • Soil texture is determined by separating the amount of sand, silt and clay in a soil and determining the % of each. • This mineral part of the soil or the Sand, Silt and Clay particles are from the weathering of Rocks and Minerals. • Soil texture is the single most important physical property of the soil. Knowing the soil texture alone will provide information about: • 1) water flow potential, • 2) water holding capacity, • 3) fertility potential, • 4) suitability for many urban uses.
Rocks Weather to Soil • Weathering is the process by which all rocks at the earth's surface get broken down. • Weathering occurs by both chemical (decomposition) and mechanical processes (disintegration).
Physical Weathering • Physical weathering - Rocks get broken into pieces but its chemical composition remains unchanged. • Processes of Phys.Weathering • 1) Freeze / thaw weathering - occurs when temperature freezes at night and rises during the day. Water expands when frozen which forces rocks open. • 2) Biological weathering _ Roots of plants grow into cracks and force cracks open. • 3) Exfoliation - when rock at earth's surface is worn away. • After a rock that has formed deep in the earth is exposed at the surface it expands and gradually breaks into sheets.
Chemical Weathering • Chemical weathering -Rock broken down by chemical change - water always plays a part. For Example: • Carbon dioxide dissolves in rain water forming carbonic acid which dissolves limestone rock which is carried away in solution as calcium hydrogen carbonate. • Chemical weathering is faster for limestone than sandstone and is speeded up by heat.
Chemical Weathering • Common chemical weathering processes are: hydrolysis, dissolution, and oxidation. • Chemical weathering produces clays on which vegetation can grow. • A mixture of dead vegetation, clay, rock fragments of sand and silt size particles produces soil.
Weathering • Weathering is controlled largely by climate. The more water available, the more likely that chemical processes can proceed. • Additionally, in warm temperatures chemical weathering can proceed even faster.
Weathering • In arid climates, however, weathering processes move very slowly. • Mechanical weathering will be the dominant process in arid climates; • however, because physical weathering relies on chemical weathering, it will also be quite slow
Soil as a Resource • WHAT DOES SOIL DO? • Healthy soil gives us clean air and water, bountiful crops and forests, productive rangeland, diverse wildlife, and beautiful landscapes. • Soil does all this by performing five essential functions:
Soil as a Resource with 5 essential functions:1) Regulating water. • Soil helps control where rain, snowmelt, and irrigation water goes. • Water and dissolved solutes flow over the land or into and through the soil.
2)Sustaining plant and animal life. • The diversity and productivity of living things depends on soil. • The more productive the soil, the more diversity in both the plant and animal community.
3) Filtering potential pollutants. • The minerals and microbes in soil are responsible for : • filtering, buffering, degrading,immobilizing,and detoxifying organic and inorganic materials, including industrial and municipal by-products and atmospheric deposits.
4) Cycling Nutrients. • Carbon, nitrogen, phosphorus, and many other nutrients are stored, transformed, and cycled through soil. • This is a good thing for it keeps them out of our water systems.
5) Supporting Structures Buildings need stable soil for support, the bearing capacity determines the ease of stable construction.
Deforestation • The main contributors to land degradation are erosion and soil compaction, as a result of extensive removal of vegetation, exposure of the soils to heavy rainfall, increased evaporation, and later wind action.
Agriculture • Agriculture may last for a few hundred of years or it may last for thousands of years. • Agave production on these fields in Mexico may last for fewer than 50 years due to soil erosion which results in the loss of valuable topsoil.
Water Erosion • Water erosion is the wearing away of soil particles. • Raindrops detach the soil particles. • As infiltration is reduced, water moving down slope takes the soil with it.
Wind Erosion • Wind erosion is the detachment of soil particles by the wind and moving them to another location.
Chemical Degradation • Chemical spills can pollute the soil beyond which it can recover naturally. • Soil remediation can reclaim the soil, making it useful again.