EPSC 413 Final exam

Northern peatlands

Contain one-third of global soil carbon, accumulate and store carbon and release CH4. Farming peatlands increases mineralization, reduces CH4 release but increases CO2 release. Thawing peatlands underlain by permafrost increase both CH4 and CO2 emissions

Population growth and agriculture

Before agriculture 1000 ha could support only one family. Agriculture allowed the same land to support 100 families. Since the industrial revolution population has exploded. More food has been produced in the last 60 years than in the prior 10,000 years. Increased food production resulted from more land being cultivated and increase cropping intensity. Increased agriculture has positive and negative effects of soil quality.

Mechanisms of soil OM stabilization

Biochemical recalcitrance, chemical stabilization, and physical protection. Carbon can also be stored in soil aggregates

Limiting the impact of nutrients on the environment

Biological systems can be designed to promote nutrient uptake or denitrification. Buffer strips reduce nutrient loads in runoff by capturing and using nutrients before they enter water bodies. Constructed wetlands remove N through denitrification. There is a great potential to improve nutrient recycling in modern systems. Nutrient recycling can lead to substantial improvements of soil quality.

Surface complexation

Both cations and anons can bind to sites on the external surfaces of soil minerals. Cations show increasing adsorption with increasing pH. Anions show increasing adsorption with decreasing pH.

Physical weathering

Breakdown of rocks into smaller particles without a change in composition. Caused by wind, water, and ice

Wind erosion

Cause of soil loss in arid and semiarid regions. Has caused major damage to agricultural soil in sub-saharan Africa, the former soviet Union, and the US. 40% of the soil erosion in the US occurs by wind. Most substantial in the great plain states. Wind erosion can damage crops and bury plants where the eroded material is deposited.

Small-scale soil variability

Changes in soil properties across a field. Often reflects spatial differences in parent material or effects of organisms, including humans. Often overlooked on soil maps. Example: location of manure pile causing small scale variability in nutrients.

Medium-scale soil variability

Changes in soil properties across a landscape. Varies because of differences in parent material type and age, topography, and moisture conditions.

Large-scale variability

Changes in soil properties across a state, nation, or the world. Primarily controlled by vegetation and climate, with parent material playing a secondary role.

Biogeochemical weathering

Chemical breakdown of rock-forming minerals. Produces solutes and secondary minerals. Driven by water, oxygen, and biological chemicals. Four types of reactions, Congruent dissolution, incongruent dissolution, oxidation-reduction, and complexation/chelation.

Soil associations

Collection of soil series that often occur together. Each occupies a specific landscape position. Soils vary with slope, drainage, parent material etc.

Soil sulfur

Component in some amino acids, various vitamins, many enzymes, and critical elemtn in proteins. Plant foliage contains .15-.45% sulfur, one tenth as much as N. Plants deficient in sulfur have growth problems.

Soil pH measurements

Field pH measurements used colored organic dyes that are pH-sensitive. not very accurate and can be hard to use for soils with strong colors. Laboratory-based pH measurements use 1:1 soil to water suspension and measure pH with an electrode. Low pH=Acidic High pH=Basic (Alkaline) 6.6-7.3=neutral

Key processes in soil N cycle

Fixation: N2 to R-NH2 Ammonification: R-NH2 to NH4+ Nitrification: NH4+ to NO3- Assimilation: NH4+ or NO3- to R-NH2 Denitrification: NO3- to N2

Xeric

Found in mediterranean climates (cool, moist winters and warm, dry summers); long period of drought in summer.

Adsorption of inorganic contaminants

Heavy metals often adsorbed to oxides and clays in soils. Example, heavy metals adsorb to iron oxide coatings on wetland grass roots.

Potassium and soil fertility

High levels of K are present in most minerals soils, more potassium is present than any other nutrient. Most potassium is unavailable to plants, contained in primary silicate minerals or in clays, where it is non-exchangeable. Potassium may readily leach from soils, leaches faster than phosphorus.

Causes of C release from land use changes

Human activities increase the natural release of CO2 from soil by OM decomposition and respiration. Activities that increase CO2 release include, deforestation and biomass burning, plowing, drainage of wetlands and aquic soils, increased temperature of agricultural soils.

Humans and soil erosion

Humans cause more erosion than nature. Direct connection between agriculture and erosion, erosion of agricultural fields is at least 100 times greater than the rate of soil production.

Lead in Urban soils

Humans have deposited large amounts of lead in soils, primarily from automobile exhaust. Airborne lead content correlates to airborne soil (soil dust), also correlates to childhood blood lead levels. Lead in urban soils causing increase in blood lead levels.

Soil mapping

Identifying the soils in the area and delineating the boundaries. You then map the soil boundaries onto aerial photos by considering typical soil associations and variation with topography and landscape position.

Entisols

If none of the stuff above matches its an entisol. Lack B horizons and most other diagnostic properties. Many have an ochric epipedon, many are sandy or very shallow.

Loss of potassium in soils

In acid soils there is high K leaching losses At higher pH K is better retained

Sulfur in organic matter

In surface soils 90-98% of the S is contained in organic matter. C:N:S spproximately 100:8:1. Three forms are thought to dominate: Reduced S in sulfides, disulfides, thiols, thiophenes, proteins, and amino acids. Intermediate redox states in sulfoxides and sulfonates. Oxidized S in ester sulfates.

Rill erosion

Initial sheet flow eventually concentrates into small channels, forming rills. Promoted by sloping surfaces. Sheet and rill erosion responsible for the most erosion by volume

Organic phosphorus compounds

Inositol phosphates make up 10-50% of organic P. Phosphate bound to sugar-like molecules. Stable under both acidic and alkaline conditions, binds to soil OM, only digestible by microorganisms. Remaining organic P is mostly unidentifiable to date, likely associated with soil OM as phosphate esters, 1-2% is in the form of nucleic acids and phospholipids.

Field mapping methods

It is essential to examine soil profiles in the area. For each profile you must Identify the horizons, determine diagnostic features, and assign to a soil series

Forms of potassium in soil

K in primary minerals, such as feldspars (90-98%), unavailable to plants. Nonexchangeable K in secondary minerals, such as illite and vermiculite (1-10%), slowly available to plants. Exchangeable K on soil colloids, such as smectites and OM (1-2%), readily available to plants. K+ in the soil solution (0.1-0.2%), readily available for plants.

Positive effects of intensified agriculture on soil quality.

Land use: Increased production from productive, level soils, prevented expansion into easily degradable land. Soil Nutrient Content: Maintained or increased levels of macronutrients in soil, supplied from outside sources (Manure, fertilizer), N, P and K level often enhanced. Soil organic matter: Increased plant production increases crop residues, possibly maintains or increases soil OM levels, but tillage and fertilizer may increase OM mineralization.

Conditions conducive to micronutrient deficiency or toxicity.

Leached, acid, sandy soil: Parent material low in micronutrients, leaching removed any originally present. Organic soils: deficient parent material, complexation with OM binds any micronutrients that are present. Micronutrient losses: Intensive cropping, micronutrients removed at harvest; soil mining. Eroded soil, available micronutrients washed away. Extreme pH: Acid conditions make Mo unavailable and have toxic levels of metals; under alkaline conditions most metals are unavailable but high (toxic) molybdenum concentrations exist. Waste disposal: Organic wastes applied to soil provide micronutrients, but repeated application causes toxicity.

Sulfur associated with soil minerals

Less common form of sulfur in most minerals. Sulfate minerals: Gypsum, found in subsurface horizons of arid and semiarid soils. Sulfide minerals: Pyrite and Mackinawite, found in wetland soils, especially in coastal areas, and in mine tailings. Produces acid sulfate soils when oxidized. FE and Al Oxide/Kaolinite: Adsorbed SO42-, sulfate adsorbs to mineral surface via surface complexation, dominant form of sulfur in oxisols.

Breakdown by microorganisms

breakdown by microbes is the most important degradation pathway.

Difficulty in measuring the pH of calcareous soils

pH value of water in contact with calcareous soil is controlled by the CO2 content of the soil gas. There is not single pH value for calcareous soil, must specify CO2 concentration in the air.

Mineralization

is the process of converting organic N (R-NH2) into ammonium (NH4+). Carried out mostly by microbial enzymes. Also called ammonification; carried out by ammonifiers.

Distribution of N on Earth

78% of the atmosphere is N2 gas. Useless for life, must be fixed into reactive N for use by life. Reactive nitrogen: Any form of N available for life, N bonded to H, O, or C. Most of the reactive N is found in soils.

Chemical forms of P in soils

<0.1% of the total P in soil is available to plants, this is phosphate (PO43-) dissolved in the soil solution, phosphate concentrations in soil water are generally much lower than that of N or S. The remaining 99.995 of P occurs as Organic phosphorus, in OM and dissolved forms. Calcium-bound inorganic phosphorus, dominant inorganic form in alkaline soils. Iron or aluminum-bound inorganic phosphorus, dominant inorganic form in acidic soils. Soil P on average is ~50% organic and ~50% inorganic, all forms slowly contribute to P in soil solution, but each group is very insoluble and unavailable to plants.

Soil taxonomy

A comprehensive classification system for soils. Hierarchial structure, based on soil properties that can be observed and measured (Diagnostic soil horizons, clay type and content, base saturation). Well-documented, publicly available information.

Lithosequence

A set of soils occurring across a sequence of parent materials. (medium-scale variability)

Toposequence

A set of soils occurring along a change in topography. (medium-scale variability)

Chronosequence

A set of soils occurring in similar parent materials of varying age. (medium-scale variability). Example: formation of spodosol, lecture 26 slide 15

Organic depositis

Accumulation of organic matter in wetlands leads to organic soil formation. Forms in bogs, fens, swamps, and marshes, often called peat.

Major soil forming processes

Additions, transformation, translocations, and losses.

Processes controlling inorganic contaminant fate in soils

Adsorption, ion exchange, surface reduction/oxidation, structural incorporation, extraction, leaching, conversion to a less toxic form

Climate effects on soil formation

Affects soil formation by controlling the amount of rainfall and the temperature, this is reflected in the dominant vegetative cover, different soil types dominate different climate zones, but there are always exceptions. The deepest weathering occurs in equatorial and temperate regions because that is where rainfall is concentrated. Regions often display clear climosequences.

The Kesterson efffect

Agricultural fields in arid or semiarid regions are irrigated. Irrigation water may contain moderate Se concentrations derived from Se-rich rocks. Evapotranspiration in fields concentrates selenium. Concentrated selenium leaves in field drains. Drainage water stored in holding ponds, which serve as wetlands for migratory birds. Implicated in elevated Se levels in at least 9 locations in the western U.S.

Soil order suffixes

Alfisols: -alfs Andisols: -ands Aridisols: -ids Entisols: -ents Gelisols: -els Histosols: -ists Inceptisols: -epts Mollisols: -olls Oxisols: -oxs Spodosols: -ods Ultisols: -ults Vertisols: -erts

Forms of N taken up by plants

Ammonium (NH4+): Plants take up directly, convert into organic nitrogen (R-NH2), Ammonium uptake tends to reduce soil pH. Nitrate (NO3-): Plants take up and reduce first to nitrite (NO2-), then to ammonium (Through hydroxylamine (NH2OH)) Nitrite (NO2-): Some plants may use NO2- but it is toxic in even moderate conditions. Amino acids and proteins (R-NH2): Ready to use

Potassium in soils

An essential nutrient, influences osmotic balance in cells, important in neuron function and muscle contraction, essential for N fixation and photosynthesis. Good supply of K is needed for crop production. Plant leaves contain 1 to 4% K. Potassium deficiency is bad.

Reduced till

Any other tillage leaves 15-30% of residues on soil surface

Conventional till

Any tillage that leaves less than 15% of residues on the surface

Soil moisture regimes

Aquic, Udic, Perudic, Ustic, Aridic/torric (hot aridic), and Xeric. Regimes are divided into boundary and central regimes, example: Typic Ustic vs Udic Ustic

Xenobiotics

Artificially synthesized compounds that do not exist in nature. Generally toxic and resistant to decay. May have structures similar to natural compounds but with element substitutions. May enter soil by organic waste application or spillage, as component of discarded machinery, in lubricant or fuel leaks, as military explosives, or as sprays applied for pest control. Pesticides are the most common xenobiotic substances in soil.

Types of tillage

Conventional tillage, No-till, ridge till, mulch till, and reduced till

Tillage

Conventional tilling causes substantial soil erosion, exposes oil to water and wind, pushes soil downhill on sloping surfaces. Two technological developments allowed for reduced tilling, development of herbicides and development of machinery to plant seeds in soil covered by plant residue.

Immobilization/Assimilation

Convert NH4+ into organic N. Abiotic or biotic, plants, fungi, and microbes all are capable of N immobilization.

Nitrogen fixation

Converts the inert gas N2 to reactive nitrogen, source of N for almost all life. N-fixationis carried out by Rhizobium species, actinobacteria, cyanobacteria, and methanogenic archaea. No eukaryotes can fix N: purely a microbial process. Requires the nitrogenase enzyme, substantial energy input, and low O2 environment.

Symbiotic fixation without Nodules.

Cyanobacteria fix comparable quantities of N as legumes, do so in cavities in leaves. Various N-fixing bacterial species inhabit the rhizosphere, obtain food from root exudates. widespread, but rate of fixation is far lower than nodule forming species

Negative effects of intensified agriculture on soil quality

Degraded soil structure, development of micronutrient deficiencies, soil acidification from use of nitrogen fertilizer, excess nutrients: lost from soil run off, causing eutrophication, Salinization caused by irrigation in arid regions, insecticide and herbicide usage decreases soil biodiversity and contaminates drinking water, reduced production of non-cereal crops, reduced use of N-fixing legumes, monoculture causes plant disease from micronutrient deficiency or pathogen buildup, intensified agriculture reduces biodiversity, concentrated animal feeding operations damage water quality and hinder nutrient recycling

Leaching and runoff of organic contaminants

Depends on their solubility and adsorption, some compounds are highly water soluble, others are soluble only in oils and solvents, high water solubility favors leaching losses. Leaching is favored in soils with high water movement, greatest leaching hazard in sandy soils low in OM. Herbicides tend to be more mobile than fungicides or insecticides.

Dominant forms of lead in soil

Deposited as aerosols from combustion or from paint. Smelters: primarily as galena or anglesite Paint: primarily lead carbonate Automobile exhaust: lead halides and organic lead. These forms weather over time in soil. Lead weathered from initial materials binds tightly to soil organic matter and iron and manganese oxide minerals through adsorption. Adsorbed lead is the dominant form in most soils.

Steps of soil erosion by water

Detachment of soil by rain drops, transportation by moving water, and deposition of the sediment by water

Key diagnostic features used in soil classification

Diagnostic horizons: Surface (epipedon) and subsurface, Chemical properties: Base saturation, specific cation saturation, CEC activity class: CEC/% clay in soil, Mineralogy and particle size classes, moisture and temperature regimes, other unique soil features.

Micronutrients are also toxic.

Difference between deficient and toxic level can be small. Soil pH is a major control on when micronutrients are available and potentially toxic. Three ranges of micronutrient concentration, deficiency range, sufficiency range, and toxicity range.

General role of micronutrients in plants

Electron carriers in enzymes that perform oxidation-reduction reactions. Fe-S cluster and Mo-Fe-S clusters in nitrogenase. Act as bridges between enzymes and target substrates. Active site is many enzymes that perform essential biochemical processes. Involved in cell growth and division. Micronutrients help in plant growth when at sufficient levels in the soil, required in small concentrations.

Additions

Energy (from sun), water, oxygen, organic matter, dust, nitrogen, chlorine, sulfur, minerals, soluble substances (salts), iron, silica, carbonates, and other forms of energy.

Losses

Energy (radiation), water (evapotranspiration), nitrogen (denitrification), carbon (CO2 oxidation), nutrients (uptake by plants), Soil material (mineral and organic, as erosion), soluble substances, leaching of iron, silica, and carbonates.

Damage from soil erosion

Eroded soil material was more fertile than the material that is left behind. Erosion removes OM and fine material, leaving coarse material behind. Eroded material contains five times as much OM and N and 2-3 times as much P and K as soil that remains. Remaining soil has lower water holding capacity, lower CEC, less biological activity, lower nutrient supply. Remaining soil has poor structure, reducing infiltration and encouraging more erosion. Negatively affects water quality. Natural erosion rates are highest in semiarid areas.

Losses of Ca and Mg from soil

Erosion by water, crop removal and leaching. Large amounts of Ca and Mg are lost from soils through leaching. In natural ecosystems replaced by mineral weathering and dust deposition. Highly weathered soils can be nearly completely leached of Ca and Mg.

Calcium in soils and plants

Essential macronutrient for all plants. Plant foliage contains between 0.1 and 5% calcium, some require 1-3% in their leaves. Trees store large amounts of Ca in their woody tissues, net Ca uptake in tree is comparable to N uptake. Major component of middle lamella of cell wall, involved in cell growth and division, protects cells against toxicity from other elements.

Organic sulfur compunds

Ester sulfate, sulfonate, sulfoxide, and thiol (from most oxidized to most reduced). Ester sufates generally make up less than half of organic S. More reduced species common, ester sufates more common in well-aerated plowed soils. Soil microorganisms breakdown (Mineralize) these compounds and release sulfate ions (SO42-)

Inorganic contaminants

Exchangeable and dissolved forms are most available for plant uptake but tend to be in low concentrations. Many exist as surface complexes, adsorbed onto oxides, clay minerals, and OM. Availability is strongly affected by pH. Redox reactions can alter contaminant adsorption

Forms of inorganic soil contaminants

Exchangeable, bound to OM, adsorbed to minerals, incorporated in common minerals, and as distinct solid phases. Cannot be broken down.

Biota effects on soil formation

Localizes organic matter and soil development (Islands of fertility in arid environments), mixes the soil, inputs organic matter and organic acids and removes water via transpiration, trees cycle cations through the soil. Cation availability affected by ability of plants to cycle base cations.

Forms of Mg in soils

Main source of magnesium in soil is exchangeable Mg on clays and humus. Plant uptake and leaching reduce this pool. This is replenished by mineral weathering. Some Mg is released through OM mineralization. In unpolluted forests much of the Mg taken up by trees may come from atmospheric deposition.

Non-symbiotic N fixation

Many free-living N-fixing microorganisms are present in soil. Complex associations of heterotrophs fix N in many minerals soils. N-fixation likely occurs inside soil aggregates where O2 concentrations are low. Autotrophs such as cyanobacteria fix N in wetlands and soil surfaces.

Photodegradation and chemical breakdown

Many pesticides breakdown on the soil surface when exposed to sunlight. Many compounds also breakdown through chemical reactions in soils.

Nitrification

Microbial oxidation of NH4+ to NO3-. Bacteria oxidized NH4+ to nitrate to gain energy. Nitrate binds weakly to soil minerals and OM and is highly susceptible to being lost by leaching.

Denitrification

Microbial reduction of NO3- to N2 gas. 2NO3- → 2NO2- → 2NO(g)↑ → N2O(g)↑ → N2(g)↑ Occurs under low-O2 conditions. N2), a greenhouse gas, may be lost through volatilization before being reduced to N2. NH4+ and NO3- can also be leached from the soil.

P adsorption in acid soils

Most fixation in acid soils occurs by adsorption. It is fixed by adsorption to Fe and Al oxides and by forming Fe and Al phosphates under acidic conditions. Increases with time, most soils can fix a large amount of P. OM inhibits fixation by binding to surface of oxide minerals

Inorganic P in soils

Most inorganic forms of P have low solubility, phosphorus generally has the lowest concentration in the soil solution of any nutrient. Inorganic P is immobile in soil. Concentration in soil solution is limited by, the solubility of P-bearing minerals and the adsorption of P on soil particles. Factors limiting P differ in acidic and alkaline soils.

Soil degradation

Most soil degradation is the result of erosion. Soil degradation leads to accelerated ecosystem damage and human poverty.

Symbiotic fixation by legumes.

N fixation occurs in root nodules of legumes. Fixation inhibited if soil is too acidic or has excess nitrogen. Root nodules provide food to N-fixing bacteria and keep out oxygen, which block N-fixation. Symbiotic relationship between legumes and bacteria.

Consequences of lost nitrogen

N lost via denitrification has no negative impacts. N2O is a greenhouse gas. N lost via leaching and runoff contaminates groundwater and stimulates algal blooms. NH3 emissions rain out elsewhere, increasing available N in aquatic systems.

Ammonia (NH3) volatilization

NH3 gas can be produced by: breakdown of OM and manure, certain N fertilizers, and processes that raise soil pH. Ammonia may leave soils through volatilization. Ammonia is in equilibrium with ammonium, more volatilization at high pH, compounds that produce ammonia raise pH.

Ammonium fixation by clays

NH4+ ions attracted to clays and humus like other cations. Held in exchangeable form, important process preventing rapid leaching from soil. 2:1 clays, especially vermiculite, may fix amonium. NH4+ just the right size and charge, interlayer collapses around NH4+, NH4+ becomes non-exchangeable.

Forms of N in soils

Nitrate (NO3-), Nitrite (NO2-), Nitric oxide (NO), nitrous oxide (N2O), Nitrogen (N2), Hydroxylamine (NH2OH), ammonium (NH4+), ammonia (NH3), organic N (R-NH2).

Importance of Nitrogen to plant growth

Nitrogen is an essential component of amino acids, the building blocks of proteins, a component of enzymes, nucleic acids, and chlorophyll. Nitrgoen addition stimulates plant growth. Plant foliage contains 2.5-4% nitrogen. Nitrogen deficiency leads to loss of green color in plants, decreased plant growth, and oversupply can be toxic to plants and cause overgrowth.

Nutrient management

Nutrients enter anthropogenic systems as fertilizer, leave in crops and in runoff, nutrient imbalances are common in many systems. Nutrient management seeks, the cost-effective production of high quality crops, efficient use and conservation of nutrient resources, maintenance of enhancement of soil quality, and protection of the greater environment. Poor nutrient management leads to eutrophication.

Forms of P in soil change during development

Occluded=fixed: precipitated and strongly adsorbed Non-occluded=not fixed: in soil solution and weakly adsorbed Mineral=Calcium phosphate (apatite) in parent material.

Alluvial parent material

Occurs on floodplains. Floodplain deposits are often layered. Also often contains coarse material in former channels. Transported parent material

Organic versus sustainable farming

Organic farming avoids the use of any synthetic or non-biological materials, sustainable farming preserves resources for future generations without impossibly high costs today, organic farming often improves soil quality but organic farming is not necessarily sustainable.

Translocation

Organic matter moving into A horizon, air diffusion, water transport, eluvation (movement out of a soil horizon) and illuvation (movement into a soil horizon) of clay (from A to B horizon), iron, humus carbonates, pedoturbation (mechanical mixing of soil), and nutrient cycling.

Sources of sulfur

Organic matter, soil minerals, and S gasses in atmosphere. In natural ecosystems sulfur is recycled.

Mineralization of organic P in soil

P in soil can be mineralized and immobilized by the same processes as S and N. Mineralization depends on temperature, moisture, and tillage (Plowing), same dependence as for the degradation of soil OM. Mineralized P will be fixed in a mineral form if not taken up quickly by plants.

Inorganic P in alkaline soils

P is fixed as calcium phosphate in alkaline soils, form poorly soluble solid phases. P becomes progressively incorporated into more insoluble forms the longer it is in the soil. This is a major limitation on P availability in calcareous soils in arid and semi arid regions, low P availability in aridisols, inceptisols and mollisols of arid regions.

Phosphorus and soil fertility

P often limits soil fertility in natural systems, the phosphorus content of soil is relatively low, common P compounds are mostly unavailable to plants. P in fertilizer is often quickly fixed, only 10-15% is taken up by plants in the year of application. Agricultural soils in developed countries are often saturated with phosphorus. Agricultural soils in developing countries are often deficient in phosphorus.

Factors controlling soil formation

Parent material: Soil precursor Climate: Temperature and precipitation Biota: Native vegetation, microbes, soil animals, humans Topography: Slope, aspect, landscape position Time: Duration of exposure of parent material to weathering

Strategies for sustainable soil management

Plan crop rotations to improve pest management and enhance soil fertility, grow cover crops that can be used as green manures, compost livestock manures and apply to soil, move to intercropping and companion planting, encourage biological pest control, perform only conservation tillage, promote fungal growth to enhance nutrient uptake, create field buffer strips to limit erosion and provide habitat for beneficial insects. Not all of these currently can be applied together and future research is needed to enhance soil sustainability.

Law of the minimum

Plant growth is constrained by the essential element (or other factor) that is most limiting

Controlling soil erosion by water

Plant residue on soil surface, grassed waterways, terraces and flow control, and cultivation practices all affect soil erosion by water.

Magnesium

Plants take up less Mg than Ca. Constitutes 0.15-0.75% of foliage. One-fifth of magnesium in plants is found in the central component of chlorophyll, required for photosynthesis.

Chelators of micronutrients

Plants, fungi, and microorganisms release compounds (exudates) into soil in order to aide in the acquisition of micronutrients, most common targets are Fe and Mo. Non-specific chelators are primarily low-molecular weight organic acids: oxalic acid, citric acid. Specific chelators are often siderophores, compounds that target an element, typically Fe, with high specificity. Produced plants, fungi, and bacteria.

Strategies for Fe acquisition

Some plants will locally acidify the soil to make Fe available. Other plants use siderophores. Directly: release siderophore, take up after chelting Fe. Indirectly: release siderophore, steals Fe from other chelates.

Specific soil forming processes

Podzolization: Processes associated with spodosol formation; Migration of both OM and Al (±Fe) to the B horizon, leaving an E horizon Andisolization: Process of ash weathering, binding of OM, and formation of short-ranged order minerals Calcification: Formation of secondary carbonates Salinization: Accumulation of soluble salts - Solonization: Illuvation of salts into B, forming Btn Melanization: Darkening of A by addition of OM Gleization: Process of gleying; iron reduction

Properties of soil K

Potassium is the third most likely element to limit plant growth after N and P. Potassium exists almost exclusively as K+, does not form any gases, behavior of potassium in soil is controlled by cation exchange and mineral weathering, potassium causes no problems such as eutrophication and is non-toxic.

Sustainable soil management

Practices that satisfy the growing need for food, fiber, and biomass while maintaining or enhancing soil quality and the environment

Soil carbon sequestration

Requires removal of atmospheric CO2 by plants followed by storage in soil as OM, increases SOC concentration in soil, improve depth distribution of SOC, stabilize SOC in micro-aggregates to prevent degradation or as recalcitrant SOC. A number of practices are recommended to enhance carbon sequestration, conservation tillage, cover crops, crop rotation, nutrient recycling, and many more. Incorporating biochar into soil may provide a large, long-term C sink. Biochar is exceptionally recalcitrant in soil.

Saprolite

Residual parent material that retains some semblance of the original rock structure. Typically only seen for granitic igneous and metamorphic rocks. Often found in areas of intense weathering.

Mechanics of Wind erosion

Saltation: Bouncing Suspension Blowing in the wind Creep: Rolling and sliding

Examples of soil contamination

Selenium contamination of the Kesterson national wildlife refuge and Lead in urban soils

Serpentine soils

Serpentine soils form on serpentinite rock. Serpentine soils have Ca:Mg rations of 1:3 to 1:9, Ca deficiency is a major problem. Soils also are low in N, K, and P, and have high concentrations of heavy metals, like Ni and Cr. metal toxicity is exacerbated by deficiency. Some plants are endemic to serpentine soils. Often barren

Examples of soil testing methods

Soil Coring for bulk density measurements, Time domain reflectometer used to measure water content, tensiometer used to measure matric potential. Soil sampling for nutrient analyses, sampling depth and number of samples depends on the desired test and the nature of the soil surface.

Adsorption of organic chemicals

Soil OM and high surface area clays are strongest adsorbents. Contaminants with many charged groups or a large size are more strongly adsorbed. Some organic compounds with positive charge will cation exchange.

Time effects on soil formation

Soil development is fundamentally a temporal process. The more time the soil forming factors have to act, the greater the soil development. Clear time-series progressions of soil development are seen in specific climates.

Relationship between erosion and CO2 release

Soil erosion and degradation in general leads to a reduction in soil organic carbon (SOC). Loss of SOC does not mean CO2 is released, SOC is redistributed by erosion, some is deposited and mineralized, releasing CO2, the rest is buried and sequestered, erosion releases 1.1 Pg of C/yr to air. Erosion is a major control of SOC depletion on sloping land.

Pedogensis

Soil forming processes acting to create and transform soils.

Residual parent material

Soil forms in place by weathering of local bedrock. Parent rock can be found at depth. Soil chemistry and mineralogy strongly controlled by composition of original bedrock.

Aridic/Torric (Hot aridic)

Soil is dry for at least half of the growing season; moist for less than 90 consecutive days

Aquic soil moisture regime

Soil is saturated/flooded and free of oxygen for much of the year; gleying and mottling

Udic and Perudic

Soil moisture sufficient year round to meet plant need. Perudic: extremely wet, excess moisture for leaching

Strategies for reducing soil lead, and therefore blood lead levels.

Soil removal or capping: Excavation of contaminated surface soil and/or addition of soil with lower Pb content. Hurricane Katrina an example Phytoremediation: Attempts to use plants to extract soil lead have had poor results, but stabilizing soil with ground cover reduces human lead exposure. Phosphate addition: Phosphate can make lead more insoluble, but many challenges to implementation remain. Addition of biosolids/compost or biochar: These may lower lead bioavailability and promote vegetation, lower soil dust levels Enhancing soil moisture: Irrigation of soils in the dry season decreases dust level, reducing exposure to soil lead.

Sheet erosion

Soil removed uniformly except where the surface is protected. Soil detached by raindrops runs off in sheet flow. Sheet and rill erosion responsible for the most erosion by volume

Mulch till

Soil surface tilled prior to planting, but at least 30% of crop residues are left on surface; weed control by herbicide and tillage. Reduces erosion, brings erosion rates in line with production rates

Soil temperature variability

Soil temperature varies seasonally and with depth. Average soil temperature reflects mean annual air temperature. Temperature variability affected by vegetation and soil physical properties. Solar radiation heats the soil and promotes evapotranspiration. South facing slopes receive more solar radiation and thus warmer and dryer.

Ridge till:

Soil undisturbed before planting, which is done on ridges; weed control with herbicides and tillage; top of ridge sliced off annually. Reduces erosion, brings erosion rates in line with production rates

No-till

Soil undisturbed before planting, which occurs in narrow seedbeds; weed control with herbicides. Reduces erosion, brings erosion rates in line with production rates

Soil contamination

Soils have become contaminated with toxic organic and inorganic materials through accidental release and deliberate application. For example, application of sewage sludge, atmospheric deposition of smelter emission, and industrial accidents and deliberate waste dumping.

Soils and greenhouse gases

Soils store more C than plants and atmosphere combined, cultivation increases OM decomposition releasing CO2, different agricultural practices may increase soil OM. Wetlands are important stores of C and sources of greenhouse gases, 20% of global soil C stored in Histosols and Histels, release CH4 and N2O. CH4 decomposition occurs in soils, inhibited by N fertilization

Vertisols

Soils with 30% or more clay to a depth of 50 cm and shrinking/swelling properties. Commonly have slickensides, Bss horizons, and develop deep, wide cracks when dry.

Inceptisols

Soils with a cambic, sulfuric, calcic, gypsic, petrocalcic, or petrogypsic horizon, or with a mollic, umbric, or histic epipedon, or with an exchangeable sodium percentage (ESP) of >15% or a fragipan. Cannot have an argillic, kandic, natric, oxic, or spodic horizon. Soils with any diagnostic horizonz are at least an inceptisol.

Mollisols

Soils with a mollic epipedon and a base saturation of > 50% (Relatively high) to an impermeable layer or at 1.8m from soil surface. Many have an argillic, natric, or calcic horizon. Some have a duripan or a petrocalcic horizon. Formed under grass or savanna vegitation, deep root system very important.

Spodosols

Soils with a spodic horizon within 2 m of soil surface and without andic properties. Commonly have an albic horizon and an ochric epipedon. Form under forest vegitation, contains short-range-order minerals. Look for Bh, Bs, Bhs horizons below an E horizon.

Ultisols

Soils with an argillic or kandic horizon and a base saturation of <35% (Low) at 2m depth or 75m below a fragipan. Might have an ochric epipedon, looks for Bt horizon.

Alfisols

Soils with an argillic, kandic, or natric horizon or a fragipan with clay skins. Relatively high content of bases (> 50%). Typically have an ochric epipedon. Some have a duripan, a fragipan, or a petrocalcic horizon. Most formed under forest or savanna vegetation. Look for Bt horizon. (if all the same stuff but a base saturation of <35% than its an ultisol)

Aridisols

Soils with an aridic soil moisture regime (dry) and some B horizon development or a salic horizon. Have one or more of the follwing diagnostic horizons: an argillic, calcic, cambic, gypsic, natric, petrocalcic, petrogypsic, or salic hroizon or a duripan. Typically have an ochric epipedon. Generally have a B horizon. Might have desert pavement

Oxisols

Soils with an oxic horizon within 150 cm of soil surface. Have clay fraction with a low cation-exchange capacity and have very few weather-able minerals. Have an oxic or kandic horizon and most commonly an ochric epipedon. Most formed under tropical forests. Look for Bo horizons. red color

Andisols

Soils with andic properties (Low density, glass, pumice, short-range-order minerals). Contain large content of volcanic materials. Commonly have a cambic horizon and can have any diagnostic epipedon, look for melanic epipedon.

Histosols

Soils with organic soil materials extending down to an impermeable layer or with an organic layer that is more than 40 cm thick and without andic properties. Dominated by organic material, commonly found in bogs, moors, peats, or mucks. Thick O horizons.

Gelisols (Classification works like this, go down the list, if not the one above then it could be...)

Soils with permafrost within 100cm or cryoturbation within 100 cm plus permafrost within 200cm. Look for Bf, Bff, and/or Bjj horizons.

Urban soils

Some argue that another soil order should be added for urban soils, Anthroposols. Soil materials have often been redistributed by human activities. Profiles often contain building debris or buried horizons or wastes.

Ustic

Some plant-available moisture, but significant dry period or drought

Types of soil tests

Standard tests: pH, neutralizable acidity, organic matter, phosphorus, potassium, calcium, magnesium, cation exchange capacity, fertilizer recomendations Specialty tests: Secondary and minor nutrients, Nitrate-n and ammonium-N, specialized N and P tests, sodium tests for arid soils, base saturation, particle size analysis, heavy metals and other contaminants.

Naming of lower levels

Suborder: Generally reflect moisture or temperature regime Great Group: Defined largely by the presence and arrangement of diagnostic horizons. ("Hapl-" means a group in the suborder with no distinguishing features) Subgroup: Defined by additional diagnostic horizons or properties ("Typic" subgroups are those that display the central properties of the great group) Families: Described by the chemical and physical properties Series: Type soil, named after a location or geographic feature.

Forms of sulfur in soil

Sulfate (SO42-), sulfate esters (R-C-O-SO3), sulfonates (R-C-SO3), sulfite (SO32-), sulfur dioxide (SO2), Sulfone (R-S(=O)2-R), sulfoxide (R-SO-R), sulfonium (R-S-R2), elemental sulfur (S), organic disulfide (R-SS-R), Disulfide (S22-), Thiols (R-SH), and sulfide (S2-)

Haploidization

The destruction or blending of existing soil horizons. (Horizons are disappearing: change in soil type)

Horizonation

The formation and/or differentiation of parent material into discrete soil horizons. (New horizons are forming: change in soil type)

Anthropogenic effects on the global carbon cycle

The pre-industrial carbon cycle is thought to have been largely balanced, humans have increased CO2 over the last few thousand years, we release additional CO2 from fossil fuel burning and land use changes, oceanic CO2 uptake has increased and there is currently an unidentified terrestrial CO2 sink. Net atmospheric increase of 4.1 Pg of C per year

Gully erosion

When water flow is high, rills can coalesce into gullies. Rill and sheet erosion are responsible for most soil losses, but gully erosion is the most severe, catastrophic, and irreversible. Gully erosion has destroyed vast tracts of agricultural land throughout history.

Pesticides

They are chemicals designed to kill pests. Insecticides: Kill insects that harm crops, livestock, or people Herbicides: Kill weeds that compete with or kill crops

Processes affecting the dissipation of organic chemicals in soil

They can be volatilized, adsorbed (especially to OM), lost through leaching, runoff, and erosion, and broken down by light, abiotic chemical processes, and microorganisms. Overtime organic contaminants become entrapped in soil OM.

Forms of Ca in soils.

Three main pools of Ca in soil: Ca-containing minerals, calcium-humus complexes, exchangeable calcium on clays and humus. Most calcium taken up by plants comes from exchangeable Ca and Ca in easily weathered minerals like calcite. Substantial amounts of calcium are deposited from the atmosphere in dust.

Topography effects on soil formation

Topography acts as a large-scale control that modifies the other soil forming factors. Affects rainfall and temperature, which affects the biota present and the extent of weathering.

Colluvial parent material

Transported downslope by erosion (e.g., a landslide); formed from local parent material. Transported parent material

Ways to control wind erosion

Trees (windbreaks) slow the wind, reducing erosion. Wetting the soil surface reduces wind erosion.

Soil calcium-Magnesium tation

Typical Ca:Mg ratio of about 6:1. 1:1 to 15:1 are all ok for plants, plants can meet their nutrient needs, soil aggregation and biological activity unaffected, low ratios (below 1:1) can cause problems for grazing animals and, at 1:6 and below, plants

Soil phosphorus

Very important for ATP, DNA, RNA, phospholipids, bones, and teeth. Healthy leaf tissue contains 0.2-0.4% P, about one tenth of N content. Enhances plant growth, enhances photosynthesis, N fixation, flowering, fruiting, etc. Dissolved phosphate in the soil solution is the only form of P accessible to plants. Mycorrhizal fungi important for accessing fixed P

Reduction in erosion

We have reduced soil erosion by 40%. But soil is still eroding 60 times faster than it is being produced.

Transformations

Weathering of minerals, formation of new minerals, changes in organic matter (degradation) by mineralization and by soil animals.

Volatilization

When organic contaminants leaves the soil as a vapor. Soil fumigants are volatile and are rapidly lost from the soil after treatment, some herbicides and fungicides are volatile enough for this to be their primary means fo loss from the soil, gasoline, diesel, and many solvents vaporize when spilled on soil. Some chemicals that volatilize may return to the soil in rain.

Loess

Windblown silt deposits, typically found in areas near glaciers or draining glacial meltwater. Becomes productive farmland after soil development. Highly susceptible to erosion. Transported parent material

Eutrophication.

excessive richness of nutrients in a lake or other body of water, which causes a dense growth of plant life and death of animal life from lack of oxygen. Caused by poor nutrient management. Nutrient runoff promotes algal blooms, when these die they sink to the bottom, microbes consume all the bottom water oxygen as the dead algae decay. In freshwater systems is induced by P, in marine eutriphication caused by N, not P.

Weathering

turning parent material into soil. Two types, physical and biogeochemical weathering. Changes the composition and mineralogy of a system. Clay mineralogy reflects the extent of weathering and the climate. Soil orders vary in the extent of weathering that has occurred.