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SOS 1102 Soils and Fertilizers Definition of a Soil • A collection of naturally occurring, dynamic, three dimensional bodies on the earth’s surface. • Consist of the upper physical, chemical, and biological portion of the earth’s crust. • It contains living matter and is capable of, or has been capable of supporting plant growth. For purposes of growing plants Mixture of organic and inorganic solids, air, and water all interacting with each other and the plant. Man is dependant on soils for • Habitat for crops • construction • sewage disposal • recreation Early civilization built on good agricultural soils. History of the study of soils • • • • • 1000 BC Homer 400 BC Xenophon 1590 Sir Hugh Platt 1600 Sir Francis Bacon 1652 Von Helmont • • • • • • • • 1699 1727 1731 1804 1840 1850 1886 1912 Woodward Stephen Hale Jethro Tull N. T.deSaussure Von Liebig Way & Lawes Dokuchaiev Coffey Soil studies can be divided into two disciplines Edaphology Pedology Parent material • Unconsolidated and partially weathered mineral and/or organic matter from which the upper part of the soil is developed by various weathering processes. Three Basic Types of Rocks • Igneous - formed when molten lava/magma cools • Sedimentary - formed from mineral and/or organic fragments which are deposited and recemented • Metamorphic - igneous or sedimentary rock which has been changed by heat and pressure Igneous rock in the making Lava flow movie Rock cycle Plate tectonics Three Classifications of Parent Material • Residual - rock weathered in place • Cumulose - organic matter deposited in place due to saturated conditions • Transported - parent material which have been moved before being weathered and forming a soil Catagories of Transported Parent material • Moved • Moved • Moved • Moved by by by by water wind ice gravity Parent material moved by water Three categories moved by water • Alluvial • Lacustrine • Marine Alluvial • Sediments deposited by flowing water –flood plains –terraces Lacustrine • Materials deposited at the bottom of fresh water lakes Marine deposits • Sediments deposited by rivers into oceans Parent material moved by wind Too much of a good thing! Parent material moved by ice Four Types • Terminal moraine • Lateral moraine • Ground moraine • Outwash plain Parent material moved by gravity Colluvial materials Weathering of parent material • Physical • Chemical Physical Weathering • Heating and cooling • Freezing and thawing • Wetting and drying • grinding action Chemical weathering • Reactions which cause changes in structure hydration hydrolysis oxidation carbonation reduction • Reactions which cause changes in solubility Factors affecting soil formation • Type of parent material – effectiveness of weathering processes – nature of the plant material • Climate – Precipitation – temperature • Topography •Biosphere - type and amount of organic matter •Time - younger soils tend to be less fertile Soil Morphology Study of the nature and shape of the soil profile What is a soil profile??? • An exposed vertical cut through the soil body exposing the soil horizons. • What’s a horizon? A zone in the soil parallel to the surface. Erosion exposed this profile • Erosion from a major storm exposed this profile at Talbot Island State Park Notice the layer of black humus Soil horizons are differentiated by • Color • Soil chemistry • texture • consistence • organic matter content • structure Six master horizons • O, A, E, B, C, & R • Not every soil exhibits all horizons • Buried ancient soils my be found deeper in soil • Roman numerals and subscripts give additional information about a horizon O horizon A horizon • organic material at the surface • greater than 20% organic matter • most common in undisturbed forested areas or wet areas • Oi OM identifiable • Oa more highly decomposed • Is or was at or near the surface • mineral layer with an accumulation of organic matter • loss of clay and some nutrients • higher in sand and silt • develop relatively fast E horizon • zone of maximum loss (eluviation) • light color ("bleached") • low clay, organic matter, and nutrients • higher in sand and silt • take a very long time to develop B horizon • zone of maximum accumulation (illuviation) • accumulations of clay, iron oxides, humus (organic matter), and/or carbonates • shows moderate to strong structure development • take a long time to develop C horizon R horizon • parent material • loose (can dig with a shovel) • weak or no structure • weatherd from bedrock, or transported and deposited • Bedrock • Hard & solidified Soil Taxonomy Order12 Sub order 47 Great group 230 Sub group 1,200 Family 6,000 Series 13,000 Phase Soil taxonomy Order - based on major set of soil forming processes Sub order - temperature, vegetation, wetness Great Group - based on soil horizons and their arrangement Sub group - variation around central theme Family - based on properties important to plant growth Series - group of individuals uniform in differentiating characteristics Phase - surface texture, stoniness, drainage, salinity Examples of complete classification of several soils Twelve Soil Orders • Entisols • Vertisols • Inceptisols • Aridisols • Mollisols • Andisols • Spodosols • Alfisols • Ultisols • Oxysols • Histosols • Gelisols Alfisol Have a noticeable clay horizon, gray to brown surface horizon, forest soils of north central U.S. and Canada Andisols • formed in volcanic ash/volcanic material, typically dominated by hydrous oxides of aluminum, fix large amounts of phosphorus, mountains of the Pacific Northwest, portions of Alaska and Hawaii. Aridisols Develop in dry climates, low in organic matter, B horizon just developing. One of the largest soil orders in the U.S. Entisols Mineral soils with lack of significant profile development, found in a wide range of climates Gelisols contain permafrost close to surface, generally poorly suited for agriculture, difficult to build on, polar regions, high mountains, and Alaska. Histosols Organic soils, 25% to greater than 90% organic matter, form anywhere saturated conditions exist Inceptisols Young soils in which the profile has developed quickly, Appalachia Mollisols Dark colored agricultural soils of the mid west, granular structure, high fertility, high percent base saturation Oxysols Most highly weathered soil order, have surface horizon dominated by hydrous oxides of iron and aluminum, near equator Spodosols Have a spodic horizon, (I.e. a subsurface horizon dominated by clay) NE U.S., Canada, Fl. GA. Ultisol Moist soils that develop in warm climates, have a noticeable red or yellow clay horizon, S.E. U.S. Vertisols High content of swelling clay, Mississippi, Louisiana, Texas FL. Entisols, Ultisols, Spodosols • Tend to be low in: nitrogen, sulfur, magnesium • Low organic matter • Low CEC • Mostly sandy • Low pH • Low organic matter • some Ultisols may be deficient in phosphorus Florida Histisols & calcareous Entisols • Histisols tend to • Calcareous be very highly Entisols occur in organic, 90 coastal south percent or Florida areas. Low greater. Very CEC, high pH, 7.2 fertile however to 8.0 are poorly drained Land Capability Classes • Roman Numerals • I - IV suitable for agriculture • Roman Numerals • V - VIII not suitable for agriculture but may have valuable functions Poor soil conservation practices • In the 30’s drought combined with poor soil conservation practices to create the “dust bowl” in Oklahoma and several other mid western states. The social upheaval associated with this place and time is chronicled in John Steinbeck’s classic novel “The Grapes of Wrath”. Dust Bowl Movie Importance of “topsoil” • The dramatic increases in yield associated with thickness of topsoil (ie. Relative amount of erosion) is illustrated by this data from a 3 year study done in Missouri. The rest of the story • Notice that yield is also associated with pH. The lower 1/3 of the field had been previously limed. Not Harvested Land capability classes Class I- few limitations, row crops every year 0 to 2% slope Class II - row crops every 2 years, terraces for slope 2 to 6% slope Class III - severe limitations, row crops every 3 years 6 to 10% slope Class IV year very severe limitations row crops forth 10 to 15% slope Land capability classes Class V - not suitable for agriculture because of special conditions (i.e.. Rocky, wet, climate) Class VI - severe erosion, light grazing or forestry 15 to 25% slope Class VII - mountainous regions, forestry, recreation 25% + slope Class VIII - mountain peaks, coastal marshes, may be useful for ecological areas, recreation, etc. Land Capability Class Subscripts Roman Numerial E W Example: S IIIE C Soil Survey • Consist of a set of base maps and a bulletin • Classify the soils in an area • Locate the different soil series on a base map • Describe the nature of the various soils as they occur in the field Edaphology Soils are a 3 phase system Ideal Soil 50% solid space & 50% pore space Nitrogen oxygen carbon dioxide Sand, silt, & clay 1/2 available 1/2 unavailable 25 % air 25 % water 45% mineral solids 5% organic solids Solid phase - physical properties • Soil texture - the relative proportions of various particle sizes in the soil • Soil structure - the degree and nature of how the soil particles are bound together Effects of soil texture • CEC • water holding capacity • infiltration and percolation of water • pattern of water movement • gas exchange between soil and air Soil Textural Separates Whole soil Sand 2.00 - 0.05mm Silt 0.05 to 0.002 mm Clay less than 0.002 mm Sand • Low CEC • low fertility • Low water holding capacity • low plasticity and stickiness • Rapid infiltration and percolation • rapid gas exchange • resist compaction • higher bulk density Silt • CEC somewhat higher than sand • moderate plasticity and stickiness • infiltration and percolation somewhat slower than sand • Bulk density intermediate between sand and clay • could be best described as “micro” sand Clay • High CEC • High fertility • very plastic and sticky • high water holding capacity • Very slow infiltration and percolation rate • bulk density lower than sand and silt • “heavy” to cultivate • narrow range of moisture for cultivation Relative differences in textural separates • • • • • • • Very coarse sand coarse sand medium sand fine sand very fine sand silt clay › › › › › › › 8 foot beach ball 4 foot beach ball medicine ball basketball softball poker chip flake of oatmeal Soil textural triangle • Soil textural class is determined by physical analysis to determine percent composition of sand, silt, and clay then using this information in conjunction with the textural triangle. Loams • A loam is a soil whose properties are not dominated by a single textural separate • It is not an equal mixture of sand, silt, and clay • Relatively small quantities of clay tend to a disproportionate affect on a soil’s properties Determining texture by feel Sand Silt Clay Clay forming a ribbon Soil structure Unstructured - single grained soil Structured- soil containing aggregates Soil structure Importance of desirable aggregates • Improved infiltration and percolation • less runoff • less erosion • improved drainage • better gas exchange Improving soil structure • Add organic matter • proper pH and liming practices • avoid cultivating in wet conditions • avoid traffic on wet soils • manage sodium problems Describing soil pore space • Macropores (non-capillary) - large soil pores which will not hold water against the force of gravity • Micropores (capillary) - small pores which hold water against the force of gravity Calculating soil pore space • Particle density - the weight of the solid divided by the volume of the solid measured in grams per cubic centimeter (2.65 g/cm) • Bulk density - weight of the soil divided by the volume of the soil Calculating soil pore space continued • Particle density = pd (2.65 standard value) • Bulk density = bd (measured in lab) • % solid space = bd/pd X 100 • % pore space = 100 - % solid space Properties of water • Hydrogen bonding Properties of water • cohesion - the attraction of water for itself • adhesion - the attraction of water for charged surfaces • surface tension - cohesive forces at work at the waters surface • capillarity - rise of water in small pore spaces due to adhesion and cohesion Forms of soil water • Gravitational water - water which drains freely due to the force of gravity • capillary water - water held in smaller soil pores against the force of gravity • available water - capillary water available for plant uptake ( -1/3 atm to -15 atm) • hygroscopic water - water held in a thin film around the soil particle Soil moisture constants • Field capacity (FC) - maximum amount of water the soil can hold against the force of gravity, -1/3 atm tension • permanent wilting point (PWP) - plant can no longer obtain water from the soil, - 15 atm • Soil saturation - gravitational water present above -1/3 bars The range of soil moisture Determining soil moisture • Tension tables are used to develop soil moisture release curves Generalized soil moisture release curve Generalized soil moisture release curve Soil moisture & plant growth Methods of measuring soil moisture • gravimetric Resistance method/Gypsum blocks Suction method (tensiometers) Time Domain Reflectometry TDR • A signal is sent down a metal probe, the time it takes for the signal to return to a sensor allows calculation of soil moisture. • Gives volumetric rather than mass readings • Is a good relative indicator of soil moisture throughout the entire spectrum from FC to the PWP • Recent innovations have made it affordable Mineralogy and structure of the solid phase Sand and silt Sand and silt • Composed mainly of primary minerals (i.e.. Minerals formed at high temperatures) • typical particle is inherited unchanged from of igneous and metamorphic rock • most abundant mineral in this fraction is quartz followed by feldspars • shape of sands may be an important consideration Sand shapes Sand particle shapes Sand color Clay • Composed mainly of secondary minerals (i.e.. Minerals formed at low temperatures) • typically particle is either inherited unchanged from sedimentary rock or formed over time in low temperature reactions • most abundant are the clay minerals, but also includes various oxides, carbonates, and sulfates Carbonates and sulfates • Calcite is the most abundant carbonate • gypsum is the most abundant sulfate generally more common in arid or semi arid regions Oxides • Typically formed in larger quantities in soils depleted of silicone by leaching • usually abundant in highly weathered soils • consist of hydrous oxides of Fe, Al, Mn • structure ranges from crystalline to amorphous Clay minerals • Most abundant component of the clay fraction • are tiny layer silicates • have a tremendous impact on soil properties Building blocks of clay minerals Silicone tetrahedron Alumina octahedron Layering of clays • Although the line drawings make it appear there is a lot of empty space in the crystal lattice of clays, in reality the atoms are very tightly packed. Examples under scanning electron microscope Finely divided mica kaolinite dickite montmorillonite Why do clays have such high CEC’s? • Amount of surface area • charge obtained through isomorphic substitution Clay minerals are differentiated by • Number and sequence of silica and alumina layers • layer charge • interlayer bond or cation • cation in the alumina layer Comparison of common clay minerals Example of expanding clay Other clay particles • Amorphous clays - “young” clay particles which have not had sufficient time to form crystalline structure • sesquioxide clays - highly weathered clays -hydrous oxides of iron and aluminum -low plasticity and stickiness -may be amorphous or crystalline