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Soil Science > Exam 2 > Flashcards

Exam 2 Flashcards

Modules 5-8

1
Q

What % of soil is water, air and soil solids?

A

25% water
25% air
50% soil solids

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2
Q

Range of Soil Moisture: Saturation

A

-all pore space is filled with water
-water will actively drain from soil due to gravity

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3
Q

Range of soil moisture: Field Capacity

A

-soil moisture that remains after excess water has drained
-some small air pockets in pore spaces

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4
Q

Range of soil moisture: Permanent Wilting Point (PWP)

A

-there is water in the soil, but it is so tightly adhered to soil particles that plants can’t access it

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5
Q

Range of soil moisture: Air Dry

A

-as dry as the soil can get when exposed to air
-a small amount of soil moisture remains

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6
Q

Range of soil moisture: Oven Dry

A

-no water left in soil
-all pore spaces filled with air

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7
Q

Available Water Holding Capacity (AWHC)

A

-amount of water available to plants
-AWHC= Field Capacity (FC) - Permanent Wilting Point (PWP)

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8
Q

Soil Moisture Content (SMC)

A

-amount of water that exists in soil at a particular time
-changes daily as plants take up water in their normal growth processes
-may be measured as % water by mass, % water by volume, or inches of water per foot of soil

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9
Q

Soil Moisture Depletion (SMD)

A

-amount of water that’s below field capacity
-SMD=FC-SMC

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10
Q

Management Allowed Depletion (MAD)

A

-% varies by crop/situation
-the percentage of available water holding capacity that management allows to be used up before irrigation

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11
Q

Maximum Soil Moisture Depletion (max SMD)

A

-the largest SMD is allowed to become before an irrigation
-SMD max= AWHC x MAD

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12
Q

How does soil effect water tension?

A

clay-highest soil water tension
silt-moderate soil tension
sand-low soil water tension

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13
Q

When is large MAD appropriate?

A

-hand move or wheel move sprinkler systems
-furrows and border strips with long runs or sandy soils
-specific plant requirements: moisture stress for almonds, citrus, cotton, wine grapes

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14
Q

When is small MAD appropriate?

A

-irrigation systems capable of small, frequent irrigations
-irrigation with saline (salty) water
-uncertain water supply
-specific plant requirements: root crops (carrots, onions and potatoes), stone-fruit (cherries, peaches), strawberries and corn

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15
Q

Properties of water

A

Cohesion- water molecules are attracted to each other
Adhesion- water molecules are attracted to others
Capillary Action- when liquid flows through narrow spaces without external forces like gravity
Polarity- unequal sharing of molecules

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16
Q

Why do humans modify the hydrologic cycle?

A

there is a limited amount of freshwater to accommodate to everyone’s needs

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17
Q

Evaporation

A

loss off water from evaporation from the surface of the soil or bodies of water

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18
Q

Runoff

A

water pools on soil surface and gathers in bodies of water

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19
Q

Infiltration

A

water seeps into the ground

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20
Q

Groundwater

A

water stored in the ground

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21
Q

Watershed

A

an area of land that channels rainfall, snowmelt, and runoff into a common body of water

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22
Q

Aquifer

A

a body of rock or sediment that holds groundwater

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23
Q

What is most water used for by humans?

A

Irrigation

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24
Q

What is the second largest use of water by humans?

A

Domestic

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25
Where are aquifers located in CA?
-along the coastline -one large aquifer in the San Joaquin Valley
26
Why is it an issue that the San Joaquin Valley shares an aquifer?
-no limits to amount of water being pumped -too much water being pumped and not replenishing fast enough to make up for it
27
What is SGMA?
-the Sustainable Groundwater Management Act -formed in 2014 -local groups of groundwater sustainability agencies (GSA's), which each have to form their own groundwater sustainability plan (GSP) with oversight from the state -the eventual goal is to replace as much water into the groundwater system as we pull out from wells
28
What is the impact on SGMA on Ag?
-SGMA is absolutely necessary for the sustainability of Ag and people in California -however, it doesn't come without cost. We have been over using water for a long time and now we have to pay for it -it is estimated that by 2040, farm acreage in California will decrease by 20-30% or 900,000
29
What is the primary issue with urban watersheds?
-Urban areas have high % of compacted soils and land covered with impermeable surfaces ex: rooftops, paved streets, parking lots -funnel lots of water to small sewage drains and storm drains, increasing erosion
30
What can be done to increase urban runoff?
-replace solid concrete with permeable pavers or gravel when possible -replace storm drains going to sewers with "rain gardens"--water is funneled into a landscape
31
What is evapotranspiration (ET)?
the combination of water loss from evaporation from the soil surface and transpiration water loss from plant leaves
32
How can transpiration water loss be reduced?
-reduce unwanted vegetation (weeds) -fallow land in dryland areas (larger spaces between plants, smaller plants, or plant every other year for a annual plants)
33
How can we control evapotranspiration of water from the soil surface?
-vegetative mulch: straw, leaves or other OM *can also provide weed suppression if thick enough *can be expensive and difficult to apply -Plastic mulch: plastic films on the surface of the soil *warms the soil (may be good or bad) *expensive -crop residue and conservation tillage: farming practices that leave organic matter from the previous crop on the soil surface, rather than removing it from the field or tilling into the soil
34
What strategies are used for drainage systems when there is too much water in soils?
-ditches -drainage tiles
35
Why is air required by plants in soil?
required for root transpiration
36
How do gases differ in composition in soil vs. in the atmosphere?
the partial pressure of oxygen is greater in the atmosphere and that of carbon dioxide is greater in the soil pores
37
How does water influence gas diffusion in soil?
-the more water in the soil the less gas diffusion -the diffusion of gas is 10000 times smaller through water than through air
38
How does waterlogged soil influence soil microbial activity?
-when soil microorganisms have reduced access to oxygen, some species can utilize elements other than oxygen as an electron receptor (redox reactions) -less energy efficient but allows life to continue -continued water logging increases soil pH because of chemical reactions over time -sulfur compounds are a common in redox reactions, which is why water logged soils often smell like sulfur
39
Do all plants have the same tolerance for restricted aeration in soil?
no
40
How does human activity influence soil aeration?
-soils compacted by equipment, even compacted by digging tools -soils in urban areas with impermeable surfaces
41
What are the effects of soil temperature on plants and other life?
-as soil temp increases, soil microbiological activity increases -as soil increases, plant (root) growth increases up to a certain point, then it will reduce or stop -soil also reflects heat from its surface, and it is an important part of freeze prevention and also keeps us cooler in the summer
42
How does the type of surface affect temperature?
-soil also reflects heat from its surface, and it is an important part of freeze prevention and also keeps us cooler in the summer
43
How does soil temperature compare to air temperature?
soil temperatures do not change as much as air temperatures change throughout the year
44
How does soil temperature change with depth?
as soil depth increases, temperature changes even less
45
What effects heat transfer in soil?
-bulk density -water content
46
How does tillage affect soil temperature? Why?
-tillage increases soil temperature in summer, mainly because of reduced organic matter on the soil surface CT=clean tillage (no crop residue)
47
How does organic mulch affect soil temperature?
-winter has higher soil temp -summer has lower soil temp *organic mulch acts as insulation to protect from severe weather conditions
48
How do plastic mulches affect soil temperature?
-increase soil temperature -shouldn't be used in the summer
49
What is cation exchange capacity and why is it important?
-ability of soil to adsorb & exchange cations -lots of plant nutrients are cations
50
What are some of the cations on the exchange that are important to plants?
-Ammonium (Nitrogen) -Iron -Magnesium -Potassium -Phosphorous -Manganese -ZInc -Calcium Toxic: Sodium
51
How does cation exchange work?
-elements attach to clay colloids -soil is negatively charged so positively charged particles attract to it -fertilizer nutrients exchange with particles attracted to colloid -if it doesn't get stuck to soil then it leaches
52
What kind of soil has the highest/lowest range of CEC?
-Soil Humus has the highest -Loamy Sand has the lowest
53
How does soil pH affect the CEC of organic matter?
as pH increases the % CEC provided by organic matter increases
54
How does CEC affect sorption of carbon compounds to soil? What types of compounds might this affect?
High CEC sorbs the carbon compounds faster than low CEC
55
How does clay weathering affect CEC?
-in general, clays have high CEC -however, the more weathered the soil, the lower the CEC
56
How is CEC determined?
-wash cations out of soil with ammonium solution which replaces allocations -then run a potassium solution through the soil to wash out ammonium -measure amount of ammonium in solution
57
How does CEC change the way farmers should apply cationic plant fertilizers?
it requires different management for farmers
58
How does the pH scale work?
Acids 1-6 Neutral is 7 Alkali is 8-14 *measures acidity and alkalinity of substances
59
Why is soil pH important?
-pH influences the availability of nutrients to plants -pH influences availability of toxic ions in soil
60
What is pH?
-pH is the relative concentration of H+ and OH- ions -pure water has a neutral pH and an equal amount of H+ and OH- ions -every # up or down the pH scale represents a 10-fold change in acidity or alkalinity -going up = H+ ions decrease and OH- ions increase 10x -going down = H+ ions increase and OH- ions decrease 10x -Acidic soils = larger portion of H+ ions -Alkaline soils = larger portion of OH- ions
61
Carbonic and other Organic acids
-most common contributor of soil acidity -weak acid is formed by carbon dioxide is dissolved in water -carbon dioxide is release in soil from microorganisms breaking down organic matter and roots respiring -microbes can also generate other stronger organic acids, such as carboxylic acids
62
Accumulation of organic matter
-OM binds to cations and tends to facilitate their loss by leaching -OM contains H+ as part of acid functional groups which enter the soil
63
Oxidation of nitrogen
-oxidation reaction produces H+ ions as a product -the process of nitrification of NH4+ to NO3- by microbes (either from fertilizer or OM) oxidize and release H+
64
Oxidation of sulfur
-plant residue contain -SH groups and when broken down form H2SO4 (a strong acid) -this reaction is also used to acidify soils on purpose through sulfur applications
65
Acids in precipitation
-rain, fog, snow and dust contribute. acid because water moves through CO2 in the atmosphere -this creates carbonic acid and reduces the pH of rainwater, snow, etc. from a neutral pH of 7 down to about 5.6
66
Plant uptake of cations
-plants may take up cationic nutrients (such as K+, Ca2+) rather than anionic nutrients (NO3-) and exude H+ ions into the soil solution to maintain charge balance
67
Why is soil acidity an issue?
-pH affects plants, animals and microbes -for non adapted plants, strongly acidic soil has the following issues: *many important plant nutrients arent available to plants--(calcium, magnesium, phosphorous and molybdenum -other elements are present in toxic amount-aluminum and manganese
68
Why is aluminum toxic to plants?
-it is taken into the roots but it is not translocated to the rest of the plant -it accumulates and damages cell membranes and restricts cell wall expansion -leads to short, stubby roots -the damaged root system results in stunting and lack of nutrient absorption for the entire plant -some species have adapted to aluminum toxicity
69
How is soil pH raised?
-various CaCO3 containing materials (i.e. lime) -the Ca2+ ions replace H+ and AI3 ions in soil colloids -the reduction of H+ on soil colloids increases pH
70
What is acid rain and how does it happen?
-combustion of fossil fuels and the smelting of sulfur-containing metal ores emit enormous quantities of nitrogen and sulfur containing gases -these gases react with water to form HNO3 and H204 -normal rainwater has a pH of 5.5. but acid rain usually has a pH between 4.0-4.5 (in some cases down to 2.0)
71
What are the effects of acid rain?
-soil acidification leading to less available calcium for plants and too much aluminum -damages forests and aquatic ecosystems -also results in damage to buildings and man-made structures
72
Why has the incidence of acid raid gone down dramatically in the United States?
-passage of the Clean Air Act in 1970 -regulation and tightening air standards for both NOX and SO2
73
What causes alkaline soil?
-less precipitation than evapotranspiration, cations released from mineral weathering will build up over time because there is not enough rain to leach them -cations present are mainly Ca2+, Mg2+, and Na+ -Ca2+ is most common in alkaline soils -NA+ in large amounts is toxic-strongly alkaline leading to sodic soils
74
In what way has CEC been influenced by alkaline soil?
CEC of alkaline soils tend to be higher than acidic soils of an equivalent texture
75
Calcium-rich layers in alkaline soils
-accumulations of calcium carbonate form calcitic horizon -calcareous soils (those with free calcium carbonates) can inhibit growth for some plants
76
Clay dispersion in alkaline soils
-clays in alkaline soils are prone to deflocculation or dispersion (loss of peds/colloids) -the prevents water infiltrations
77
Nutrient problems in alkaline soils
-micronutrients zinc, copper, iron and manganese are not very available (iron and zinc most commonly) -Boron deficiency is common at high pH in sandy soil (because of low boron content) and clay soil (because boron is held tightly to colloids and is not available to plants) -molybdenum is so available in high pH soils that it can become toxic to plants -phosphorous binds with Ca2+ and Mg2+ ions to form calcium phosphate compounds that are not available to plants

Soil Science (3 decks)

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