* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Fertilizers and Fertilizer Management
Survey
Document related concepts
Entomopathogenic nematode wikipedia , lookup
Arbuscular mycorrhiza wikipedia , lookup
Human impact on the nitrogen cycle wikipedia , lookup
Plant nutrition wikipedia , lookup
Soil erosion wikipedia , lookup
Soil respiration wikipedia , lookup
Surface runoff wikipedia , lookup
Soil horizon wikipedia , lookup
Crop rotation wikipedia , lookup
Terra preta wikipedia , lookup
Soil compaction (agriculture) wikipedia , lookup
Soil food web wikipedia , lookup
Canadian system of soil classification wikipedia , lookup
No-till farming wikipedia , lookup
Soil salinity control wikipedia , lookup
Soil microbiology wikipedia , lookup
Transcript
Soil Formation: Concepts, Factors, and Processes Lecture #1 Subject Outline 1. 2. 3. 4. 5. What is Soil Why do we study Soils? Composition of Soils Soil Formation- Factors Soil Formation- Processes What is soil? Concepts of soil differ greatly among users of soil • Clerk/Secretary: Soil is dirt; it may be in the wrong place • Mining engineer: Soil is material for mining ores • Civil engineer: Soil is material that support constructions • Home owner: Soil is needed to set up flower garden. • Farmer: Soil is medium to grow crops to make a living Soil as defined by scientists … natural product formed from weathered rock by the action of climate and living organisms modified by topography over a period of time. Why Study Soils? Reason 1: Soils are crucial to life Soil is an essential part, and some would argue, the most important component of the terrestrial ecosystem Soils perform vital functions Functions of soils Soil as medium for plant growth Physical support –anchors root system so that plant does not fall over. Air –Plants depend on respiration to obtain energy. Soils provide ventilation. Water – soil through pores absorb water and hold it for plants to use. Temperature moderation – moderates temp fluctuations for the roots. Nutrient elements – soils supply mineral nutrients (dissolved ions) to plants . Protection –soils protect plants from phytotoxic substances. Soil as regulator of water supplies Soil regulates both the quality and quantity of water in rivers, lakes, and underground aquifers Quantity of water supplies Some of the water may be stored in the soil and used by trees and other plants Quality of water supplies Water is purified and cleansed as it soaks through the upper layers of soil. Soil as recycler of raw materials Soils play a role in geochemical cycles Assimilate organic waste Turn it into beneficial humus Convert the mineral nutrients into plant and animal usable forms Returning carbon to the atmosphere to be used for photosynthesis again Soil as Habitat for soil organisms Handful of soil is home to billions of organisms in thousands of species How does this happen? Micro-environment differences • • • • Pore spaces Moisture Temperature Organic matter Soil as Engineering Medium Soil is firm and solid Good base to build structures Soils differ in stability Designs for structures are different for soils Physical properties influence engineering uses Why Study Soils? Reason 2: Soil is an environmental interface Lithosphere -rocks Atmosphere -air Hydrosphere -water Biosphere –living organisms Soil Composition Soil consists of four major components in three major phases: 1. Soil Air (Gas phase) 2. Soil Water (Liquid phase) 3a. Soil Mineral Matter 3b. Soil Organic Matter } (Solid phase) The relative proportions of these components influence the behavior and productivity of soils Relative Proportions of Soil Components Determine Soil Behavior and Productivity Inorganic Minerals (Soild Phase) Inorganic minerals in soils (major solid framework of soil) Soil minerals are either primary or secondary minerals Primary minerals are the minerals that formed in the original rocks. They range from large particle stones, gravels to small particles –sand, silt, clay. Secondary minerals are formed in soil by weathering of the primary minerals (examples are Kaolinite, smectites, illites etc) The secondary minerals normally are found in the clay fraction of the soil which is the fraction of the soil solids which is less the 2 micron or 0.002 mm. Clay minerals are minerals which mainly occur in the clay sized fraction of the soil. Both inorganic and soil organic matter make up the solid fraction of soil. Organic Matter (Solid Phase) Organic matter which includes living, dead and synthesized matter are continuously broken down and incorporated. OM ultimately decomposes to humus –last stage of decomposition Humus is the product of the decay of organic residues such as wood, leaves, and other biological materials. OM is also constantly lost from soil as CO2 from microbial respiration. Soil water (or soil solution) Soil Liquid Phase Water is vital to the ecological functioning of the soil. Soil solution contains water, dissolved ions, molecules and gases. Soil water is different from free flowing water in 2 ways: Soil water is held by many types of forces within the pores of the soil. Soil water is never pure but contains hundreds of dissolved organic and inorganic compounds. Soil Air (or Soil Atmosphere) Soil Gas Phase contains similar gases as found in the atmosphere above the soil But often in very different proportions. Usually higher in carbon dioxide and lower in oxygen than the atmosphere. Is highly variable in space Has high relative humidity Interaction of the Components The components interact to determine the nature of a soil e.g., soil moisture controls air and nutrient supply mineral particles control water movement Organic matter controls arrangement of minerals which influence pores that determine water and air relationships Soil Formation a) Five factors of soil formation b) Processes of soil formation Soil Profile Soils reflect their environments Tanzania Quebec Virginia Montana Sri Lanka Brazil Five factors of soil formation s = f(cl, o, r, p, t…) Where: s = any soil property cl = climate (rainfall & temperature) o = organisms (biota) p = parent material r = relief (slope aspect and position) t = time (relative age of soil formation) 1. Parent Material Soil parent material is the material that soil develops from, and may be rock that has decomposed in place, or material that has been deposited by wind, water, or ice. The character and composition of the parent material plays an important role in determining soil properties, especially during the early stages of development. E.g., The texture of sandy soils is determined by parent material Movement of water is controlled by texture of the parent material Parent material influences the chemistry of the soil Parent material influences the type of clay minerals present in soil. Rock and Mineral Weathering to form parent material (… and on to form soils) What is rock and mineral weathering? .. the modification or breakdown and destruction of the physical and chemical characteristics of rocks and minerals and carrying away the soluble products. ..the nature of the breakdown (weathering) depends on the type of material (soft or hard?) Effect of rock type on weathering rates Slate Rock Marble Rock Two stone markers, photographed on the same day in the same cemetery (Photos courtesy of R. Weil). The slate rock (metamorphosed shale) consists largely of resistant silicate clay minerals, while the marble consists mainly of calcite (metamorphosed limestone), which is much more easily attacked by acids in rainwater. Types of Rocks Igneous rocks Form from molten magma Granite and diorite Sedimentary rocks Compacted or cemented weathering products from preexisting rocks Sandstone and shale Metamorphic rocks Formed by change in the form of other rocks Gneiss, marble, and slate Two main types of weathering a) Physical (Mechanical) weathering .. Causes rocks to disintegrate into smaller pieces without affecting their composition Types/Factors of Physical weathering: Exfoliation by temperature Abrasion by water, ice and wind Disintegration by plants and animals b) Chemical weathering .. Degradation of rocks and minerals by the chemical activities of water, oxygen, and microbial action Types/Factors of Chemical weathering: 1. 2. 3. 4. 5. 6. Hydration Hydrolysis Dissolution Carbonation Oxidation-reduction Complexation 1. Hydration Process of binding of water molecules to a mineral 5Fe2O3 9H 2O Fe10O15.9H 2O Hematite water Ferrihydrite 2. Hydrolysis Splitting of water molecules into its components. Split components in turn attack the minerals. H 2O H OH KAlSi3O8 H 2O HAlSi3O8 K OH 3. Dissolution Process of hydrating of ions until they become dissociated CaSO4 .2 H 2O 2 H 2O Ca 2 SO4 2 4 H 2O 4. Carbonation Carbon dioxide dissolves in water to form carbonic acid which accelerates chemical breakdown of materials CO2 H 2O H 2CO3 H 2CO3 CaCO3 Ca 2 2HCO3 5. Oxidation-Reduction Minerals that contain Fe, Mn,or sulfur are susceptible to this reaction when exposed to environments different from the ones in which they formed. This destabilizes the mineral. 4FeO O2 2H 2O 4FeOOH Fe(II) oxide Fe(III) oxyhydroxide –Goethite 6. Complexation Biological processes produce organic acids that can form complexes with elements within the structure of a mineral thereby pooling the element from the mineral and destabilizing it. The list on the right hand side are the products of weathering of rocks Formation of Parent Materials Parent materials could be derived from the following: 1. Organic Deposits – residues of plants 2. Rock that weathered in place 3. Rock that was deposited from elsewhere Parent materials are commonly classified by their mode of deposition at their current location. 1 2 3 Types of Parent materials Types of Parent Material 1. Gravity • colluvium 2. Ice transport • glacial till, moraine, outwash 3. Wind transport • Eolian (dune sand, loess, dust) 4. Water transport • • • Lakes -lacustrine Streams –alluvium (floodplain, alluvial fans, delta) Oceans –marine 5. Volcanic ash 2. Climate May be the most influential of the four factors acting on the parent material • Determines the nature and intensity of weathering (precipitation and temperature) Both affect the physical, chemical and biological processes Climate also exerts influence indirectly through a second soil forming factor, the living organisms (natural vegetation). Climate is so important in soil formation that certain evidence of climatic change could be found in the soil Precipitation 1. Water is essential for all the major chemical weathering reactions. 2. The deeper water penetrates the parent material, the more effective it is in soil weathering and development. Water percolating through the soil profile transports soluble and suspended material from the upper to the lower layers. Thus percolating water stimulates weathering reactions and helps differentiate soil horizons. Temperature 1. Every 10 deg C, the rate of chemical reaction doubles If warm temperatures and abundant water are present in soil at the same time, the processes of weathering, leaching, and plant growth will be maximum and lead to deep soil profiles. Compare this to very modest soil profile development processes that are obtained in cold areas 3. Organisms (Biota) Soil organisms, both the animals (fauna) and the plants (flora) physically churn the soil and help stabilize the soil structure a) Role of natural vegetation Organic matter accumulation Cation cycling by trees • E.g., Grassland vs. Forest • E.g., Heterogeneous rangelands Heterogeneous Rangelands (Plants & soil formation) b) Role of animals Animals such as gophers, moles, prairie dogs bore into lower soil horizons and bring materials to the surface –tunnels. Earthworms and termites • Bring about considerable soil mixing Human influence • • • • destruction of natural vegetation Soil tillage for crop production Irrigation Fertilizer application 4. Topography Relates to the configuration of the land surface It is described in terms of differences in elevation, slope and landscape position Steep slopes encourage soil loss by erosion and allow less rainfall to enter the soil; thus prevents formation of soils, and helps destruction of soils. In the depressions where runoff tends to concentrate, the soil is usually more deep Role of Topography in Soil Formation 5. Time Time that materials have been subjected to weathering is important because soil forming processes take time to show their effects. Clock of soil formation starts when e.g. Landslide exposes a new rock Flooding river deposits sediment on floodplain Glacier melts and dumps load of debris Bulldozer cuts and fills landscape, etc. Rates of weathering and soil development This is a function of the interaction of time and the other factors of soil formation. Age of soils (Rate of Soil Devpt) Both soils are developed soils, but soil on the left is more mature than soil on the right in terms of soil horizon development Role of Time in Soil Formation Processes of Soil formation Processes of Soil formation Processes that are involved in soil formation can be placed in four main groups Additions 2. Transformations 3. Transfers or Translocations 4. Losses 1. 1. Additions Additions entail the inputs of materials to the developing soil profile from outside sources. E.g. Addition of organic matter from Plant leaves and sloughed-off roots Addition of water by precipitation Addition of dust particles that fall on the soil surface Addition of salts and silica that is dissolved in groundwater and deposited near or at soil surface 2. Transformations Transformations entail disintegration and/or altering of composition and form of organic and inorganic components of soil Physical weathering of lager particles to smaller particles Decomposition of organic residues Recombination of decomposition products to form new minerals such as silicate clays and oxides, organic acids, humus and other products Aggregation of mineral particles 3. Transfers or Translocations Translocations involve the movement of organic and inorganic materials laterally within a horizon or vertically from one horizon to the another. Movement of water Movement of dispersed fine clay particles Movement of dissolved organic substances The most common translocation agents are water and soil organisms. 4. Losses Materials are lost from the soil by the following: Drainage and leaching to groundwater Erosion of surface materials Evaporation Plant uptake Microbial decomposition Animals and humans Combination of Processes Additions Transformations Translocations Translocations Losses Combination of The Soil Forming Processes in Action (Soil Horizon Development) A-Horizon development Accumulation of organic matter Clumping of individual soil particles Distinct from parent material and other layers B and C horizon development Carbonic and organic acids are carried by water into soil where dissolve various minerals (transformations) Soluble materials (ions –Ca2+, CO32-, SO42-, etc) are carried by water and precipitate in the soil from upper to lower horizons (translocation) Weathering of primary minerals into secondary minerals Wetting and drying cracks soils and makes structures. Soil Horizon Development Result of the soil forming processes in action