Soils Management Flashcards
What is an anion
A negatively charged atom/molecule
Ex found in soils: phosphate, sulfate, nitrate, and chloride
What is a cation
A positively charged atom/ molecule
Ex in soils: Calcium, magnesium, sodium, potassium, and ammonium
Define cation exchange capacity
The amount of positively charged anions that can be held by a given weight of soil
Define anion exchange capacity
The amount of negatively charged anions which can be held by a given weight of soil
What is the unit for CEC/AEC
Centimole charge per kg soil (cmol/kg soil) or meq/100g of soil
What factors determine the CEC of soils
Percent clay
Type of clay
Amount of OM
Soil pH
What is the order of CEC for OM and various types of clay
OM 200 meq/100 g
Vermiculite 150
Montmorillonite 100
Illite 30
Kaolinite 10
What affect does pH have on CEC and AEC?
As pH increases, CEC increases, AEC decreases
What ions can become fixed to clay surfaces? How do they become fixed?
“Holes” in the clay surface allow K and NH4 to enter the space, which they clay then collapses around. This makes nutrients unavailable for plant uptake
Differentiate saline, sodic/matrix, calcareous, acidic and alkaline soils
A saline soil contained sufficient soluble salt to impair plant growth (soils that have an electrical conductivity greater than or equal to 0.4 Siemens per meter in the saturation extract are considered saline)
A sodic/natric soil has from 13-15% or more of the CEC occupied by Na. (These soils have poor structure and accompanying poor plant growth)
A saline-sodic soil has ECs greater than or equal to 0.4 Siemens per meter and from 13-15% or more of the CEC occupied by Na. These soils have good physical properties until the salty is removed and they revert to sodic
Calcareous soils contain free calcium carbonate
Acidic soils have a pH less than 7
Alkaline soils have a pH more than 7
What properties change as sand and silt decrease and clay increases?
Bulk density, particle size, and pore size decrease
Pore volume and surface area increase
What does higher surface area create?
Higher CEC/AEC
Higher surface area = more clay and/or OM
Describe how soil texture affects water holding capacity, amount of available water, and wilting point of soils
The distribution of pore size in soil impacts drainage and plant available water
Plant available water is that water which can be extracted by plants. The max value of available water is the difference between the amount of water a soil can hold after most free drainage has occurred (field capacity) and the amount of water in the soil when plants will wilt and not recover even if water is added (wilting or permanent wilting point)
How is water in the soil measured?
By weight (dry soil basis) percentage
Volume percentage
Height of water (cm/in)
Energy of retention (units are bars, atmospheres or pascals)
Define soil structure
The arrangement of soil particles into larger units of varying degrees of coherence called peds
How do Soil microorganisms affect soil structure
Soil microorganisms decompose organic matter, crop residues, and other organic amendments added to the soil.
Short term: increase aggregation through production of decomp products that “glue” soil particles together
Long term: can decrease OM levels and aggregation in conditions that favor decomp (frequent tillage, optimum temp, moisture, oxygen, and limited return of crop residues)
What are macroorganisms and how do they affect soil structure?
Termites, ants, earthworms, moles
Mix the soil and create large channels that improve aeration and drainage
Define bulk density and what determines it
The mass of oven dry soil per unit volume
g/cm3
Soil texture and structure determine bulk density of a soil
How is bulk density impacted by organic matter and farm equipment traffic?
Bulk density increases as soil organic matter decreases (due to incorporation, burning, or removal of crop residues)
Continuous tillage can increase bulk density and cause the creation of tillage pan
Compaction from implement wheel traffic and animal traffic, especially on wet soils, increases bulk density
What are sources of organic matter?
Pant/crop residues (top/root)
Green manures/ cover crops
Animal manures
Composts from ag, industry, municipalities
Biosolids (municipal sewage sludge) and industrial wastes (paper mill sludge)
Soil animals (micro/macroorganisms)
What are the physical properties of biomass?
There are pools of organic matter in soils including organic material decomposing, biomass, and organic material that has undergone various degrees of decomp.
Humus is the most stable form of OM and decomposes very slowly
When organic materials decompose, about 80% is converted to CO2 and lost from the soil. About 15% becomes humus, and 5% is biomass
What are the chemical properties of organic matter
OM retains nutrients by adsorption. Cations are held by caution exchange sites on OM. Negative charges on OM are pH dependent, as pH increases CEC (pH depended negative charge on OM) increases
Anions are held by anion exchange sites on OM. The positive charges on OM is pH dependent, as pH decreases he AEC (pH dependent positive charge on OM) increases
At normal pHs, the CEC is much larger than AEC of OM
OM increases buffering against pH changes
What are the beneficial effects of OM?
Soil particles can be linked together into aggregates by OM. As OM content increases, aggregates tend to become more water stable (resistant to breakdown by water)
Source of nutrients (primarily N, also P and S) when decomposed. Retains cations that are macro/micronutrients for plants.
Increases water holding capacity, plant available water and infiltration
Decreases crusting of soil
Increases pore size, increases aeration
How does temperature influence soil microbial activity?
Microbial activity increases as temp rises above freezing until optimum temp, once above optimum temp activity declines back to zero
For many microbial conversions, there is a two-fold increase in activity for each 10EC increase in temp from about 15-35c. Above 35c, a decline commonly occurs
How does moisture influence soil microbial activity
Aerobic microbial activity is usually optimum at 40-60% of a soil’s water holding capacity (slightly drier than field capacity)
Decline in activity typically occurs as soils become more dry, rapidly declining at a critical soil water content. Critical level varies with microbial reaction being considered
Anaerobic activity (-Oxygen) occurs in saturated souls and ceases in the presence of oxygen.
Facultative anaerobes can function in the presence or absence of oxygen
How does soil pH influence soil microbial activity?
Fungi are more active in acidic soils
Bacteria are more active in neutral to basic soils
Rates of reaction carried out by specific microorganisms change as pH changes
How does OM influence soil microbial activity
Additions of organic C to soil stimulates microbial activity
The more decomposable the organic C, the more rapid the increase in microbial activity
How does salinity influence soil microbial activity?
As salinity increases, microbial activity can decline depending on the microorganism and amount of salinity.
Microbes expend more energy to absorb water as salinity increases
Various enzymatic processes within the microbial cell can be impaired by soluble salts
How do nitrogen applications influence soil microbial activity ?
May have a wide range of impacts on soil microbial activity
In general, better fertility improves microbial activity
Can increase activity if Low N is limiting decomp
Can affect specific groups of microbes
How does tillage influence soil microbial activity?
Tillage increase aerobic microbial acivity
May have adverse long term effects (decreased OM)
How does the C:N ratio affect OM decomposition and N availability?
Nitrogen rich (low C:N ratio) organic materials (green/animal manures and sewage sludge) release large amounts of inorganic N as NH4 to the soil when decomposed because microorganisms don’t need all of the Organic N to build new microbial cells. Increases plant available N (mineralization)
Nitrogen poor (high C:N ratio) organic materials (wheat straw, sawdust) can cause microorganisms to remove large amounts of inorganic N from the soil during decomposition as the N is required to build new microbial cells. Decreases plant available N (immobilization) that becomes available later
Differentiate O, A, B, and C horizons
O: accumulation of organic matter
A: mineral horizon at the surface or below O horizon, which has lost most or all of the original rock structure, has an accumulation of om, and has often been acted upon by man
B: could have
Illumination (deposition) of clay, iron, aluminum, om, carbonates, gypsum, and/or silica
Removal of carbonates
Residual sesquioxides or coating of sesquioxides reflecting a reddish color of soil
Clay weathering
Structural development
Brittleness
C: little affected by soil forming (pedogenic) processes, but not hard bedrock
What is parent material?
The rock, I consolidated material (wind/water deposited) or om that forms soil after physical, chemical, and/or biological pedogenic processes have occurred
How do you determine the area of a field?
Break the field into squares (area=lengthwidth), rectangles (area=lengthwidth) and triangles (area=1/2length*width) with total field area being the sum of all squares, rectangles, or triangles. If measurements are made in ft, total area in acres= total sqft/43,560
Copy an areal photo of field and surrounding area, cut out field and known area and weigh each. The field area is the ratio of the field area weight to the know area weight
Use computer software that can analyze digital images for area or for length and width (google earth)
How do you determine slope?
Use a topographic map, the % slope is the change in landscape elevation in ft for a given horizontal distance in ft*100
Usually take the average of several slope determinations representing similar areas within the landscape area
What are the characteristics of a well drained soil?
Oxidized, iron and manganese are insoluble, soil has color
Good aeration
Good available water unless excessively drained soils leading to drought
Aerobic microbial processes like nitrification active
Good root and top growth
Decomposition of most organic materials
What are characteristics of a poorly-drained soil?
Reduced, iron and manganese become soluble, soil color is lost (gleyed/greed)
Mottled (areas of color) may develop in small areas surrounded by gleyed soil
Poor aeration
Excessive soil water
Poor soil structure if peds are not water stable
Anaerobic microbial processes like denitrification active
Poor plant growth unless the plant is aquatic (rice)
Slow decomp of most organic materials
Development of plant disease
Differentiate surface and subsurface drainage
Surface drainage systems include ditches, grasses waterways, levees, and precision leveled land
Subsurface drainage systems include corrugated and PVC slotted pipes, mole drains which may or may not be filled with gravel, interceptor drains at the base of a slop, and groundwater pumps (designed to lower the water table in soils)
What can limit land use
Leaching potential
Erosion potential
Runoff potential
Soil drainage class
Wetlands
Proximity to sensitive area
Describe the erosion processes detachment, transport, and deposition for wind and water erosion
Soil particles are detached from one location and transported by wind, water, or ice to a different location where they are deposited.
What types of erosion occur by water?
Sheet: thin layer of soil is removed by running water
Splash: movement of soil particles from rain impacting and breaking down soil aggregates
Rill: small channels formed by running water that are small enough for implements to pass over and can easily be filled
Gully:large channels formed by running water that will not allow passage of implements. Tillage and other implements cannot cross classical gully erosion, but can cross ephemeral gully erosion
Surface creep: slow movement of soil down a steep slope accelerated by saturated soil conditions and freezing/thawing.
What types of erosion are caused by wind?
Saltation: wind causes small soil particles to move along the soil surface in a bouncing fashion
Suspension: wind carries fine soil particles to potentially great heights over long distances
What is tillage erosion?
When tillage moves soil from the top to the bottom of a field creating a shallower soils at the top of the field and deeper soils at the bottom of the field.
What increases the rate of water erosion?
Duration and intensity of rainfall: higher intensity rain and longer duration rains increase erosion
Poor soil structure and crusting that decreases infiltration capacity
Increases slope length and steepness
What decreases water erosion?
Good soil structure
Vegetative and residue cover
What increases the rate of wind erosion?
An increase in wind duration, direction and velocity
Increases Unsheltered distances
Sandy textures can dislodge clay and silt which can move by suspension
What decreases the rate of wind erosion
Any factor that decreases wind velocity(surface roughness, wind breaks, strip crops, vegetation/residue cover)
Define the concept of soil loss tolerance
The amount of soil that can be lost by erosion and still maintain crop production on that soil from an economic standpoint over the long term.
Values range from 1 ton/ac/yr (shallow soils) to 5 ton/ac/yr (deep soils)
How does strip cropping reduce detachment and transport?
Cropped soil is protected, slope length of I cropped soil is decreased.
Cropped strips have increased infiltration and retain sediment
How does contouring reduce soil detachment and transport?
Slope is decreased when runoff moves along contours which means lower water velocity.
Slope is decreased when runoff moves along contours so sediment can settle out
How do terraces reduce soil detachment and transport?
Reduced slope and slope length, often cropped increasing infiltration.
Reduced slope and slope length, often cropped increasing sedimentation
How do grasses waterways reduce soil detachment and transport?
Main channel for water is protected from erosion by sod.
Water flows through sod at reduced velocity and sediment is deposited
How does Surface residue reduce soil detachment and transport?
Protects soil surface from running water, raindrops, and wind
Residue slow water and wind velocity allowing sedimentation
How do cover crops reduce soil detachment and transport?
Protects soil surface from running water, raindrops, and wind
Slows water and wind velocity allowing sedimentation
How can tow spacing and direction reduce soil detachment and transport?
Narrow rows allow earlier vegetative cover protecting the surface from rain and wind. Rows with a slight slope along the contour minimize runoff rate and increase infiltration.
Narrower rows increase the surface roughness trapping soil particles. Rows with slight slope along the contour reduce amount of runoff.
What are Conservation buffers and how do they reduce soil erosion?
Filter strips, grasses waterways, windbreaks, shelterbelts, contour grass strips, riparian buffers
Reduce water and wind speed, protect the soil surface and trap soil particles
How do grade stabilization structures (rock dam, concrete boxes, ponds) reduce soil erosion?
The energy in water moving in a gully is reduced by slowing water flow in the structure, decreasing detachment and allowing sedimentation.
How does surface roughness reduce soil erosion?
Wind speed is lower over some of the surface allowing suspended soil particles to deposit on rough surface.
How do wind breaks decrease erosion?
Wind speed is decreased allowing suspended soil particles to be deposited
How do you measure percent crop residue cover?
Place a 100 ft tape measure diagonally (45degrees) across the road. Look directly over the tape measure and count the number of times crop residue intersects the line at each ft increment on the left or right side for the entire length.
Percent crop residue= number of intersections per 100 increments
If using 50 ft tape measure, look at intersections every 6 inches
Do several times to get a field average
What effect does biomass removal have?
Decreases Surface OM which can reduce soil structure.
Fertility declines particularly with respect to soil N status, buffer capacity, and nutrient retention
Erosion increases due to exposed soil surface
Moisture retention declines as water holding capacity declines
Carbon sequestration declines
How do restrictive layers hinder plant growth?
Crusting and surface compaction can decrease seedling emergence
Subsurface compaction can reduce root extension and growth
Potential for low oxygen levels when compacted layer is saturated with water
How do you calculate soil water storage?
Wend= Wstart + precipitation + irrigation - runoff - evapotranspiration - Deep percolation/recharge - ground water discharge to surface water
How do you calculate infiltration?
Precipitation + irrigation- runoff
Define preferential flow
During or immediately after precipitation/irrigation, soil can be saturated or near saturated. The water in macropores can move very rapidly downward through the soil
What is evapotranspiration?
The evaporation of water from the soil surface + transpiration of water from plant surfaces
Differentiate irrigation methods
Furrow: Water flows down a path, made by tillage equipment, between crop rows.
Sprinkler: water is applied to the soil from overhead nozzles
Drop/trickle: water is applied at a low volume to specific soil areas by emitters (drop) or small hoses (trickle)
Flood: used where slopes are small or field has been precision leveled. The field is surrounded by levees. Where slopes occur, levees are constructed along the contour. The levees have gates that control water level and allow passage of water from one levee to the other. Water enters at the high point and exits at the low point.
Subsurface: water is applied through buried tubes that contain openings
Differentiate the different drainage methods
Subsurface drain/tile: a line of tiles is placed in the soil to lower the depth of the water table to the depth of the tiles. Spacing of tiles is dependent on permeability of the soil (more permeable, wider spacing)
Ditch: a ditch that drains surface waters or subsurface water from tile lines
Raised beds: implements are used to create raised areas of soil separated by drainage ways. Raised areas drain more quickly than surrounding drainage ways.
Land leveling: fills low areas of a field where surface drainage is poor and creates uniform drainage surface in the desired direction
How are field soil moisture measurements and water balance equation used to schedule irrigation?
Soil moisture deficit = soil moisture deficit of previous day - ET + irrigation + rainfall - runoff
To schedule irrigation:
(Present soil moisture deficit - initial soil moisture deficit + rain/irrigation)/ ET
How does soil texture affect tile drainage spacing and depth?
Tile line spacing increases as the rate of saturated water movement in the soil increases (spacing is larger for sandy soils than clayey soils)
Depth of the tile line is a function of the depth of the water table and the depth to which the water table can be lowered. The depth to which the water table can be lowered increases as the rate of saturated water movement in the soil increases (sandier soils)
Describe how nutrients, pesticides, pathogens, and sediments can move to off-site areas
When precipitation/irrigation rate exceeds the infiltration capacity of a soil, runoff and erosion can occur. Ag chemicals that are water soluble, pathogens, and sediments move with the runoff while ag chemicals and pathogens that are bound to soil move with eroded soil particles
Define an impaired water body
A body of water that fails to meet water quality standards set by state, local, or federal agencies. The total max daily load (TMDL) of nutrients, sediments, pathogens, metals etc are set by environmental agencies
What is eutrophication?
The nutrient enrichment of surface water with particular emphasis on increased concentrations of P, N, and organic C.
Eutrophic bodies of water tend to have low levels of dissolved oxygen, algal blooms, and excessive aquatic plant growth
What is hypoxia?
Bodies of water that have low oxygen levels detrimental to aerobic life
Differentiate parts per million (ppm), milligrams per liter (mg/L), and milliequivalents per liter (meq/L)
For waters, ppm and mg/L are equal.
Dividing ppm or mg/L by the milliequivalent weight of the ion or molecule gives meq/L
The milliequivalent weight is the atomic/molecular weight divided by the valence of the ion or molecule
Differentiate nitrate and nitrate-nitrogen nitrogen analysis
Nitrate analysis is the mg of NO3- in a liter of water
Nitrate-N is the mg of nitrogen in the nitrate form in a liter of water
What is he molecular weight of nitrate and nitrogen?
Nitrate: 62
Nitrogen:14
Mg of nitrate is 4.4x the mg of nitrogen in a given water sample
What are the health risks to humans when drinking water containing nitrate-nitrogen or coliform bacteria above the drinking water standard
Nitrate-N can cause blue baby syndrome in very young babies and the reaction of nitrates with organic compounds in water supplies forming nitrosamines.
The increase of coliforms in drinking water increases the possibility of pathogenic organisms in water which can cause a number of diseases
What are the health risks to livestock of drinking high nitrate-N water
Can cause acute health problems in livestock such as difficulty breathing, rapid/weak heartbeat, lack of coordination, muscle weakness, low body temp, blue mucous membranes, and dilation of pupils.
Death occurs within hours
Chronic problems are usually reproductive
Concentrations in excess of 100 ppm nitrate-N alone or in combination with feeds high in nitrate-N can cause health effects
What is the purpose of anti-back siphoning devices?
Prevent the re-entry of contaminants into the water supply
Explain how high sediment levels affect surface water quality
They carry P and other pollutants to water supply
Can reduce biodiversity by decreasing light penetration and can fill impoundment due to sedimentation
