Exam 1 material
What is the difference between weathering and erosion?
Weathering is the breakdown( physical or chemical) of a material in to smaller or different material.
Erosion is the detachment, translocation, and deposition of a material
At what ψ m is Saturation? Field Capacity(FC)? Permanent Wilting Point?
ψm Saturation = 0 kPa
ψm FC ~ -33 kPa, can be variable from -10 to -33
ψm PWP =-1500 kPa
NOTE: must be able to interpret soil water retention curves
I am an organism that uses CO2 as a carbon source and biochemical oxidation as an energy source. What type of metabolic organism am I?
I am a chemoautotroph
Fertilizer conversions
How do you convert P2O5 --> P ?
molar mass of P = 31 g/mol O 16 g/mol
1. Look up atomic mass
2. multiply by subscripts 31*2 =62
16*5 = 80
3. add up total molecular weight 62+80 =142 g/mol P2O5
4. divide nutrient element mass by total
62/142 = .44 g P/g P2O5
A farmer applies 215 lbs/ac of 15-25-5 fertilizer to 3 acres of land. How many lbs of N have they applied in total? Note that units are given in pounds of fertilizer per acre, but you want units of lbs of N.
97 lbs
medium for plant growth
recycling system for nutrients and organic wastes
habitat for soil organisms
modifier of the atmosphere
engineering medium
system for water purification
What is the importance of soil Aeration? What processes would be affected by a soil that is well aerated?
Soil aeration is important because it drives chemical processes like microbe respiration. Affects the Eh(redox potential)
affects OM degradation, plant growth, nutrient availability, greenhouse emissions, soil color, toxins and contaminants
CN Ratios
When added to the soil what would an organic material with a CN ratio of 160:1 cause?
Alternatively a CN ratio of 9:1 would cause net mineralization
What processes can cause soil degradation?
Name 3
A soil sample plus its cylinder weighed 155 g dry. The cylinder holding the soil has a volume of 123 cm3 and a weight of 9.0 g. Assume particle density is 2.65g/cm3.
Calculate the bulk density of this soil, showing the correct units.
Db = mass/volume = (dry weight - cylinder weight)/volume
1.19 g/cm^3
What does soil quality measure?
It is a measure of ecosystem services
Rank the bond strength of the following Major Cations from weakest to strongest
Mg+2, Na+, NH4+, K+,Al+3,Ca+2
what about the hydrated radius?
Na+ < K+=NH4+<Mg+2<Ca+2<Al+3
The hydrated radius has a trend on the periodic table Going up the table increases the hydrated radius, while going down and to the right there would be an increase in charge and sorption
So Na+ would have the largest hydrated radius and the lowest sorption/charge
What acids compose of acid rain?
from NOx +H2O -->Nitrous acid (HNO2)
from SOx + H2O ---> sopheric acid H2SO4
What are 3 types of erosion? in increasing scale
sheet erosion rill erosion gully erosion
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Using a 37-10-20 fertilizer, you wish to apply 150 lbs. of N.
How much fertilizer (lbs.) do you need to apply? Round to the nearest 1 lb.
405 lbs.
define these terms: Colluvium, Alluvium, Eluviation, Illuviation
Alluvium - deposited by streams
Colluvium- Deposited by gravity ( found near hill/mountain bottoms)
Eluviation- exiting upper horizon
Illuviation- Accumulation of minerals - usually happens in horizon B
What pH range is optimal for plants and why?
pH is important because it affects the bioavailability of nutrients as well as harmful toxins to plants by affecting the mobility and leaching depending on the pH. This includes how pH affects the CEC (high pH --> high CEC)
optimal range 6.5-7 for neutral soils
Define Rhizobia, actinomycetes, and fungi
rhizobia: symbiotic bacteria that fix nitrogen in legume roots
actinomycetes: filamentous bacteria in dry alkaline soils( rain smell)
Fungi -chemoheterotrophs and are often filamentous and multicellular
How does tillage affect SOM?
tillage increases erosion which reduces SOM
Tillage also decreases aggregation, which increases O2 and decreases soil protection, reduces SOM
Specific heat capacity
How much energy does it take to raise 1g of a soil with θm= 22% 1 degree C?
given cdry soil= .2 cal/g or .8 J/g
and cwater = 1cal/g or 4.18 J/g
How to use this formula when given
% gravimetric moisture (θm):
1. Assume you have 100 g of dry soil
2. When mass of dry soil = 100g,
water mass = m water = θm , so
divide 𝜃𝑚/(𝜃𝑚 +100) to get Fwater*
3. F water+F dry = 1, so we can just
subtract 1-F water to get F dry
4. Now plug in the variables
22/(22+100) = .18 =Fwater
100/(22+100)=.82 = Fdry
Cmoist soil = Fdry*cdry+Fwater*cwater
answer is .856 cal/g
What are the master horizons in order?
O- organic litter
A- top soil / Organic matter mixed with minerals
E - zone of eluviation
B - zone of illuviation
C- unconsolidated parent material( partially weathered)
R - consolidated rock ( bedrock)
What are some management techniques that you can do to manage soil temperature.
difference between Black and clear plastic mulches(bonus question)
Plant residues
plant mulches.
Black vs clear plastic mulches(bonus question)
cover crop
tillage
moisture control
Oxidation and reduction.
2S+3O2+2 H2O→2 H2SO4→4H++SO4-2IS this reaction a oxidation or reduction
What is the valence state of S in the reactants and in the Products
Oxidation rxn
S in the reactants is +0
S in the products has a oxidation state of +6
How does phosphorus pollution cause eutrophication?
Eutrophication from fertilizer runoff gets into waterways, then with the extra nutrients in the water this causes an algal bloom, When the algae dies off it sinks to the bottom where heterotrophic algae and bacteria are able to perform aerobic respiration consuming dissolved Oxygen, eventually leading to an area in the water where there hypoxic levels of Oxygen can kill fish.
CEC from soil colloid composition
Soil composition has 16% sand 40% clay and 38% silt and 6% OM
Of the colloid clays there is 8% kaolinite , 70% vermiculite and 22% montmorillonite.
Given the CEC (cmolc/kg)
Kaolinite= 8
Vermiculite= 150
Montmorillonite= 100
Organis Matter- 200
Calculate the CEC with the given fractions
CECsoil = Fkaolinite*CECkaolinite +Fvermiculite*CECvermiculite+Fmonmorillonite*CECmontmorillonite+ Fom*CECom
CECsoil= (.4*.08)*8 + (.4*.7)*150+(.4*.22)*100+.06*200=
63.056 cmolc/kg