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Soils Test #1
| Question | Answer |
|---|---|
| what are the five key roles of soil | support plant growth, key part of hydrologic cycle, functions in recycling nutrients, provides habitat, engineering medium |
| soil supports plant growth by: (6) | provides physical support, ventilation, absorbs and stores rainwater, moderates temp, protect plants from phytotoxins, provides plants with mineral nutrients |
| what are the four fates of rainwater | runoff, groundwater, evaporation, taken up by plants |
| air and water provides what nutrients for plants | carbon, hydrogen, and oxygen |
| 6 macronutrients from soil | nitrogen, phosphorus, potassium, calcium, magnesium, sulfur |
| soil profile define | a vertical section exposing a set of horizons in a pit |
| soil horizon define | a layer of soil in a profile |
| O horizon | top later of decaying plant and animal matter, partially decomposed |
| A horizon | rich in organic matter, where plant roots are found, important in maintaining soil fertility, 2-30 inches thick |
| E horizon | intensely weathered and leached horizon, very few nutrients and little clay |
| B horizon | zone of accumulation for materials from E horizon |
| C horizon | unconsolidated rock, no biological activity |
| R horizon | consolidated rock |
| what are the soil horizons in order | O, A, E, B, C, R |
| what are transition layers | layers with properties of 2 soils - OA, AE, etc |
| what are subordinate distinctions | specific properties of master horizons (ex. Ap for plowed A horizon, Bw for weathered B horizon) |
| regolith/solum define | unconsolidated mantle of weathered rock and soil on the Earth's surface |
| what soil horizon is the topsoil | A horizon |
| what soil horizon is the subsoil | B horizon |
| how is soil formed | destructive processes (mild acids, temperature fluctuations, etc) or creative processes (formulation of new minerals and clays) |
| what are the 5 factors that affect soil formation | climate, organisms, parent material, topography, time |
| what are the 4 processes of soil formation | additions, losses, translocation, transformation |
| define parent material | original geological material |
| define residuum | formed in place from bedrock |
| sand granule size | 2.0-0.5mm |
| silt granule size | 0.5-0.002m |
| clay granule size | 0.002 or less |
| what is soil texture | proportions of sand, silt, and clay |
| what is soil structure | manner in which sand, silt, and clay are arranged together |
| aggregate (ped) define | clump of soil |
| humus define | portion of organic matter which is resistant to decay |
| what are the four uses for humus | binds mineral particles, increases amount of water held, major source of NPS, main food source for microbes |
| how do elements get into the water solution in soil | nutrients are released by decomposition OR charges on soil particles attract essential elements |
| how do nutrients get to plants (5) | root interception, mass flow (flooding), diffusion, contact exchange, exchange of soil ion within the mucigel of the root |
| active absorption of nutrients define | requires energy (ion pumps, carrier molecules, etc) |
| passive absorption of nutrients define | does not require energy (voids in root tissue, free spaces) |
| How many billion acres of land are in the world | 32.5 billion acres |
| how much of the land in the world can be farmed (in acres) | 8 billion acres |
| how much of the land in the world is currently farmed (in acres) | 3.6 billion acres |
| pedology define | study of soil genesis and development, what is a soil |
| edaphology | study of soil in plant production - what can soil do for us |
| primary minerals | minerals not chemically altered since deposition |
| secondary minerals | minerals resulting from decomposition |
| soil colloid | actual surface area of a soil ped |
| saprolite | soft, weathered bedrock |
| igneous rock define | rock formed from molten lava, quartz, granite, etc |
| sedimentary rock define | rock formed from deposition and cementation of weathered material, shale, sandstone, etc |
| metamorphic rock define | formed by change in form due to plate movement causing heat and pressure, quartzite, slate, etc |
| what are the two types of weathering | disintegration (physical breakdown) and decomposition (chemical breakdown) |
| hydration weathering define | adding water molecule to a compound |
| hydrolysis weathering define | splitting a water molecule into hydrogen and hydroxyl components |
| dissolution weathering define | dissolves in water |
| acid reactions weathering define | weathering is accelerated in the presence of acids |
| oxidation-reduction weathering define | minerals that contain iron, manganese, or sulfur are oxidized as the iron loses an electron when exposed to air and water |
| complextion weathering define | biological processes that produce organic acids |
| integrated weathering processes | various chemical weathering processes occur at the same time |
| 5 major factors that control soil formation | parent material, climate, living organisms, topography, time |
| what influence does the parent material have on the soil | soil texture, particle size, movement of water, weathering, translocation of soil particles, natural vegetation |
| residual parent material define | unconsolidated and partly weathered minerals formed from consolidated rock, FORMED IN PLACE |
| colluvial debris parent material define | deposits of rock fragments and soil materials accumulated at the base of steep slopes as a result of gravity |
| alluvial stream deposits define | deposition of sediment due to water (flood plains, alluvial fan, etc) |
| glacier ice and meltwater played what role in soil formation | they bulldozed soil, flattening it out |
| glacial outwash define | material deposited by glaciers as they moved |
| what soil formations can occur due to soil being transported by wind | loess, dune sand, aerosolic dust, volcanic ashes |
| peat define | unconsolidated soil material consisting largely of undecomposed, or only slightly decomposed organic matter accumulated under conditions of excessive moisture |
| 3 types of peat and definitions | fibric (large plant fibers), hemic (medium plant fibers), sapric (small plants fibers) |
| what role do macrorganisms play in soil formation | bring materials to surface, pedoturbation - carried out by ants, termites |
| what role do microrganisms play in soil formation | produce organic acids while breaking down organic matter |
| what is a wheat soil | dry, well drained soil |
| what is a rice soil | wet, poorly drained soil |
| pedon define | the smallest sampling unit that can characterize an individual soil |
| polypedon define | a group of similar pedons located together in a landscape |
| soil series define | a group of pedons in a field grouped together - nearly 23,000 in US |
| soil taxonomy define | science of classifying soils |
| what is an epipedon | diagnostic soil horizons that occur at the soil surface (O and A horizons) |
| soil series define | soils with similar soil profile and horizons anywhere in the world |
| what are the 3 criteria for soil classification | chemical, physical, biological |
| what are the 8 diagnostic epipedons | mollic, umbric, ochric, histic, folistic, melanic, anthropic, plagen |
| define mollic soil | thick, dark colored, high base saturation, well-developed structure |
| define umbric soil | thick, dark colored, low base saturation, well-developed structure |
| define ochric soil | pale, light in color, thin low in O.M. |
| define histic soil | organic soil material, formed in water (peat bog) |
| define folistic soil | O.M. horizon saturated for less than 30 days a year |
| define melanic soil | black due to high organic matter and volcanic ash soils |
| anthropic and plagen soils | caused by human use |
| what are the 3 diagnostic epipedons we have in MO | mollic, umbric, ochric |
| argillic horizon define | subsurface accumulation of silicate clays which have moved downward from upper horizons |
| natric horizon define | silicate clay accumulation but contain exchangeable sodium. often in columnar or prismatic soils, mostly found in dry regions |
| kandic horizon | accumulations of Fe and Al oxides, clays are low in activity and have low cation holding capacity |
| oxic horizon | highly weathered subsurface horizon high in Fe and Al oxides and low activity silicate clays such as kaolinite |
| spodic horizon | a horizon characterized by the accumulation of colloidal organic matter and aluminum oxides |
| sombric horizon | dark in color because of high organic matter accumulation, low base saturation |
| albic horizon | light colored, low in clay and oxides of Fe and Al |
| what are the 6 moisture regimes used to classify soils | aquic, udic, perudic, ustic, aridic, xeric |
| define each moisture regime | aquic is completely submerged, no oxygen and xeric is dry in summer and wet in winter |
| what soil moisture regimes is wanted for growing crops | ustic |
| what order does soil taxonomy go in | order, suborder, great group, sub group, family, series |
| what is an entisol | soil order that is very recently formed, little horizon development, 12% of US land |
| what is an inceptisol | beginning soil, more developed than entisol but not fully developed, good for crops, 9% of US soils |
| what is an andisol | volcanic ash soil, relatively young, very fertile, less than 1% of all soils |
| what is a gelisol | frozen soils, soil formation is slowed considerably, cover 8.6% of land |
| what is a histosol | organic soils without permafrost, very low bulk density soils, thick layers of organic matter, developed underwater, 1% of US land |
| what is a vertisol | inverted soil, swelling type clays, develops wide cracks in dry weather, used for rice and cotton - 2% of US soils |
| what is a mollisol | soft soil, mollic epipedon, formed under grassland ecosystems, dark fertile soils, very productive, 22% of soil in US and most in MO |
| what is an aridisol | dry soil, supports plant growth less than 90 days/year, low in organic matter, 22% of US soils, large salt concentration |
| what is a ultisol | old weathered soil, usually gray or light brown, few soluble nutrients, 10% US soils, good for production with fertilizers |
| what is an alfisol | moderately weathered soil, surfaces gray to brown in color, 15% of US soils, lots in Southern MO |
| what is a spodosol | ash colored soil, must have spodic horizon, occur only in humid climates and under forest vegetation, found in eastern US, 3% of US soils |
| what is a spodic horizon | represents a subsurface accumulation of soil organic matter with aluminum and or iron sesquioxides |
| what is an oxisol | highly weathered soil, have an oxic horizon, found in hot climates, wet year round, high in clay content, 8% of worlds soil |
| what is an oxic horizon | abcense of weatherable primary materials, kaolinite clay, insoluble minerals such as quartz, hydrated oxides of iron and aluminum |
| main 3 soil orders in MO are | mollisols (central), ultisols (Southern), alfisol (northern) |
| what is a soil suborder | name that identifies the order and describes the properties of the soil - consists of prefix and formative element - there are 70 |
| what are great groups | subdivisions of suborders, more than 400 |
| what are subgroups | division of great groups, more than 2500 sub groups, describes as adjective in front of the great group |
| what are soil families | describe particle size, mineralogy, clay activity, soil depth, etc |
| what are series | most specific, name after nearby town that soil was classified in (Newtonia silt-loam etc) |
| Munsell color chart define | standard system used to determine soil color |
| what causes soil color | iron oxides coat the surface of soil particles |
| a bright colored soil likely means | well-drained soil |
| a gray dull colored soil likely means | waterlogged condition |
| what are silicate minerals | the main constituents of all particle size classes in soil |
| what is SiO4 and why is it important | silicon tetrahedron, the main building block of common minerals |
| how does the surface area of a soil affect it | a greater surface area means a greater capacity for holding water, plant nutrients, weathering, and for soil particles to stick together as well as affecting microbial reactions |
| what forms aggregates | plant roots, organic matter, soil organisms, freeze/thaw wet/dry |
| what influences soil structure | water movement, heat transfer, aeration and porosity, and most importantly farming |
| what are the 4 types of soil structure | sphreoidal, platelike, prismlike, blocklike |
| spheroidal soil structure | round peds or aggregates |
| factors affecting aggregate stability | fungi (temporary mechanical binding), cementing action of microbial decay, cementing action of humus and iron |
| what can be done to improve soil structure | green manure, manures, algae, plant grasses, and soil conditioners |
| how do you manage soils to improve structure | minimize tillage, till when soil is properly moist, keep soils covered, incorporate crop residue and animal manures |
| tilth define | the physical condition of the soil as it relates to ease to tilling |
| what is primary tillage | moldboard plowing/chisel plowing |
| what is secondary tillage | disking/harrowing |
| particle density define | mass of a unit volume of soil, does not include pore space |
| bulk density define | mass of a unit volume of dry soil, does include pore space |
| what two factors affect bulk density | clay content (lower bulk density), porosity (lower bulk density) |
| 7 types of soil pores | interaggregate pores (biggest), intraggregate pores, macropores, mesopores, micropores, ultra micropores, cryptopores (smallest) |
| what factors affect total pore space | texture and depth |
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