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Nick - Agriculture > Soils Management > Flashcards

Soils Management Flashcards

1
Q

Describe how soil texture affects water holding capacity, amount of available water, and wilting point of soils

A

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)

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2
Q

How is water in the soil measured?

A

By weight (dry soil basis) percentage

Volume percentage

Height of water (cm/in)

Energy of retention (units are bars, atmospheres or pascals)

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3
Q

Define soil structure

A

The arrangement of soil particles into larger units of varying degrees of coherence called peds

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4
Q

How do Soil microorganisms affect soil structure

A

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)

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5
Q

What are macroorganisms and how do they affect soil structure?

A

Termites, ants, earthworms, moles

Mix the soil and create large channels that improve aeration and drainage

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6
Q

Define bulk density and what determines it

A

The mass of oven dry soil per unit volume

g/cm3

Soil texture and structure determine bulk density of a soil

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7
Q

How is bulk density impacted by organic matter and farm equipment traffic?

A

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

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8
Q

What are sources of organic matter?

A

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)

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9
Q

What are the physical properties of biomass?

A

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

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10
Q

What are the chemical properties of organic matter

A

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

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11
Q

What are the beneficial effects of OM?

A

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

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12
Q

How does temperature influence soil microbial activity?

A

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

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13
Q

How does moisture influence soil microbial activity

A

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

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14
Q

How does soil pH influence soil microbial activity?

A

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

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15
Q

How does OM influence soil microbial activity

A

Additions of organic C to soil stimulates microbial activity

The more decomposable the organic C, the more rapid the increase in microbial activity

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16
Q

How does salinity influence soil microbial activity?

A

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

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17
Q

How do nitrogen applications influence soil microbial activity ?

A

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

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18
Q

How does tillage influence soil microbial activity?

A

Tillage increase aerobic microbial acivity

May have adverse long term effects (decreased OM)

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19
Q

How does the C:N ratio affect OM decomposition and N availability?

A

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

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20
Q

Differentiate O, A, B, and C horizons

A

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

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21
Q

What is parent material?

A

The rock, I consolidated material (wind/water deposited) or om that forms soil after physical, chemical, and/or biological pedogenic processes have occurred

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22
Q

How do you determine the area of a field?

A

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)

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23
Q

How do you determine slope?

A

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

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24
Q

What are the characteristics of a well drained soil?

A

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

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25
Q

What are characteristics of a poorly-drained soil?

A

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

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26
Q

Differentiate surface and subsurface drainage

A

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)

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27
Q

What can limit land use

A

Leaching potential

Erosion potential

Runoff potential

Soil drainage class

Wetlands

Proximity to sensitive area

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28
Q

Describe the erosion processes detachment, transport, and deposition for wind and water erosion

A

Soil particles are detached from one location and transported by wind, water, or ice to a different location where they are deposited.

29
Q

What types of erosion occur by water?

A

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.

30
Q

What types of erosion are caused by wind?

A

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

31
Q

What is tillage erosion?

A

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.

32
Q

What increases the rate of water erosion?

A

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

33
Q

What decreases water erosion?

A

Good soil structure

Vegetative and residue cover

34
Q

What increases the rate of wind erosion?

A

An increase in wind duration, direction and velocity

Increases Unsheltered distances

Sandy textures can dislodge clay and silt which can move by suspension

35
Q

What decreases the rate of wind erosion

A

Any factor that decreases wind velocity(surface roughness, wind breaks, strip crops, vegetation/residue cover)

36
Q

Define the concept of soil loss tolerance

A

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)

37
Q

How does strip cropping reduce detachment and transport?

A

Cropped soil is protected, slope length of I cropped soil is decreased.

Cropped strips have increased infiltration and retain sediment

38
Q

How does contouring reduce soil detachment and transport?

A

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

39
Q

How do terraces reduce soil detachment and transport?

A

Reduced slope and slope length, often cropped increasing infiltration.

Reduced slope and slope length, often cropped increasing sedimentation

40
Q

How do grasses waterways reduce soil detachment and transport?

A

Main channel for water is protected from erosion by sod.

Water flows through sod at reduced velocity and sediment is deposited

41
Q

How does Surface residue reduce soil detachment and transport?

A

Protects soil surface from running water, raindrops, and wind

Residue slow water and wind velocity allowing sedimentation

42
Q

How do cover crops reduce soil detachment and transport?

A

Protects soil surface from running water, raindrops, and wind

Slows water and wind velocity allowing sedimentation

43
Q

How can tow spacing and direction reduce soil detachment and transport?

A

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.

44
Q

What are Conservation buffers and how do they reduce soil erosion?

A

Filter strips, grasses waterways, windbreaks, shelterbelts, contour grass strips, riparian buffers

Reduce water and wind speed, protect the soil surface and trap soil particles

45
Q

How do grade stabilization structures (rock dam, concrete boxes, ponds) reduce soil erosion?

A

The energy in water moving in a gully is reduced by slowing water flow in the structure, decreasing detachment and allowing sedimentation.

46
Q

How does surface roughness reduce soil erosion?

A

Wind speed is lower over some of the surface allowing suspended soil particles to deposit on rough surface.

47
Q

How do wind breaks decrease erosion?

A

Wind speed is decreased allowing suspended soil particles to be deposited

48
Q

How do you measure percent crop residue cover?

A

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

49
Q

What effect does biomass removal have?

A

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

50
Q

How do restrictive layers hinder plant growth?

A

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

51
Q

How do you calculate soil water storage?

A

Wend= Wstart + precipitation + irrigation - runoff - evapotranspiration - Deep percolation/recharge - ground water discharge to surface water

52
Q

How do you calculate infiltration?

A

Precipitation + irrigation- runoff

53
Q

Define preferential flow

A

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

54
Q

What is evapotranspiration?

A

The evaporation of water from the soil surface + transpiration of water from plant surfaces

55
Q

Differentiate irrigation methods

A

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

56
Q

Differentiate the different drainage methods

A

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

57
Q

How are field soil moisture measurements and water balance equation used to schedule irrigation?

A

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

58
Q

How does soil texture affect tile drainage spacing and depth?

A

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)

59
Q

Describe how nutrients, pesticides, pathogens, and sediments can move to off-site areas

A

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

60
Q

Define an impaired water body

A

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

61
Q

What is eutrophication?

A

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

62
Q

What is hypoxia?

A

Bodies of water that have low oxygen levels detrimental to aerobic life

63
Q

Differentiate parts per million (ppm), milligrams per liter (mg/L), and milliequivalents per liter (meq/L)

A

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

64
Q

Differentiate nitrate and nitrate-nitrogen nitrogen analysis

A

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

65
Q

What is he molecular weight of nitrate and nitrogen?

A

Nitrate: 62

Nitrogen:14

Mg of nitrate is 4.4x the mg of nitrogen in a given water sample

66
Q

What are the health risks to humans when drinking water containing nitrate-nitrogen or coliform bacteria above the drinking water standard

A

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

67
Q

What are the health risks to livestock of drinking high nitrate-N water

A

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

68
Q

What is the purpose of anti-back siphoning devices?

A

Prevent the re-entry of contaminants into the water supply

69
Q

Explain how high sediment levels affect surface water quality

A

They carry P and other pollutants to water supply

Can reduce biodiversity by decreasing light penetration and can fill impoundment due to sedimentation

Nick - Agriculture (10 decks)

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