Soils exam 3
‑ What is meant by a fertilizer rating such as "10-20-5"
10%N 20% P2O5 5% K2O
‑ What is the best C/N ratio for a finished compost mixture?
10-20:1
‑ What is the ideal initial C/N ratio of a good compost mixture? What should the finished compost C/N ratio be?
25:1 - 35:1
‑ What pH range is typical for calcareous soils?
7-8.4
Acid Cations in soils
Al and H
Which base and/or acid cations would be present on the CEC complex at pH 6?
Al(OH), Ca, Mg, K
‑ Which base and/or acid cations would be present on the CEC complex at pHs 3?
Al, H, Ca
‑ What factors influence soil heating?
Albedo (fraction of incident radaition reflected), aspect (direction of slope), soil cover (vegetative cover)
‑ Approximately how long should the composting process take?
Around a year
‑ What range of soil pH is preferred by most bacteria? Most fungi?
Bacter pH>5.5 and fungi more acidic soils
‑ What is base saturation? How do you calculate base saturation?
Base cations/Total CE x 100
‑ What are important considerations for making a good compost mix?
C/N ratio, porosity, moisture content, pH, temperature, and climate
‑ What beneficial soil properties does soil organic matter contribute to?
CEC, WHC, organic NPS, soil quality, tilth
Are CO2 levels in soil pores higher or lower than in the atmosphere? O2 levels?
CO2 is higher in soil pores while O2 is higher in the atmosphere
‑ What are the "base" cations in soils?
Ca, K, Mg, Na
Which base and/or acid cations would be present on the CEC complex at pH 8?
Ca, K, Na, Mg
‑ What types of soils can have very high pHs? Why?
CaCO3 leeches base cations
‑ What is saline soils?
ESP = 0-15, EC = 4<, pH<8.5
‑ What is saline-sodic soils?
ESP = 13-55, EC = 4<, pH<8.5
‑ What is sodic soils
ESP = 13-55, EC= 4>, pH>8.5
‑ What are some examples of soil organisms?
Earthworms Ants, and bacteria
‑ What is the typical pH in different climates, such as eastern vs western US?
Eastern US =. 3.5-6.5 Western US - 6.5-8.5
‑ What are the different steps in the nitrogen cycle? What chemical forms are found at each step?
Fixation N to BM N, Mineralization, Organic N to NH4, volatilization Nh4 to NH3, Nitrification NO2, No3, Denitrification N2O to N
Fixation vs Nitrification vs Denitrification vs Volatilization
Fixation makes biomass N, nitrofication turns NO2 to NO3, denitrification turns N2O to N, Volatilization turns Nh4 to Nh3
‑ What types of materials would have high C/N ratios? Low C/N ratios?
High C leaves, staw, wood chips. High N vegetable scrapes, coffee grounds, grass clippings
‑ What are the general properties of: peat moss
High cost, low weight, 3.5-4.5 pH, high CEC, High nutrients, Medium Macro, High Micro, High water holding
‑ What are the general properties of: vermiculite
High cost, low weight, 7-7.5 pH, High CEC, High macroµ porosity, High water holding
‑ What are the general properties of: perlite
High cost, low weight, 7-7.5 pH, low cec, High macro, low micro, High water holding
‑ What is the "perching effect" and how does it impact potting media/containers?
Holding of water/saturation of rooting zone leading to poor O2 exchange
‑ How do oxygen levels vary with depth below the soil surface? CO2 levels?
Increase in depth the lower CO2 and higher oxygen soils
‑ What are some common products used to increase soil pH?
Increase soil pH with pine or acidic peat moss, sulfur, acid forming fertilizers
‑ What chemical additives need to be added to most potting mixes?
Lime, wetting agent, and fertilizer
‑ What are the general properties of: sand
Low cost, high weight, 6.5-7.5 pH, low CEC, High macro, Low micro, Low water holding
‑ What is the difference between a macro- and micro- nutrient?
Macro needed an abundance micro needed in a small amount
‑ What is pH? How do you measure pH?
Measure of balance between H an OH measured by pH paste, electrodoe meters,
Mineralization vs Immobilization vs Leaching
Mineralization turns organic N to NH4, immobilization truns NO3 to N, Leeching is the removal of NO3
‑ Which macronutient is used in the highest amount by most plants?
N
‑ What are the three main macronutrients that can be released as organic matter decomposes?
N P S
‑ What is the general order for elements to be reduced in soils as the redox potential decreases?
N, Mn, Fe, S, C
‑ Are target or ideal pH ranges for plants grown in potting media similar to natural soils?
Natural soils demand a lower pH than potting media
‑ Why are wetting agents added to peat moss prior to use as a potting media?
Naturally hydrophobic so its hard to wet and rewet initially
‑ What are the major loss pathways of environmental concern for nitrogen? For phosphorus?
P is erodided to soil particles and NO3 leeches
‑ What is the pH of rainfall? Normal pH range in soils?
Rainfall = 5.6, soil range = 3.5-8.5
‑ Why is lime added to peat moss?
Reduce acidity
‑ What are the six essential macronutrients that are supplied by the soil?
S, P, Mg, Ca, K, N
‑ What is electrical conductivity (EC) measuring?
Salinity of soil water
‑ What are the trade offs of using sand vs perlite?
Sand and perlite are both have the same properties, sand is heavier while perlite is lighter
‑ What are some materials that have high macroporosity?
Sand, perlite, pine bark
‑ How do you know when the composting process is finished?
Temperature at the center matches ambient, oxygen concetration grater than 10%
‑ What are some common micronutrients?
Zn, Mn, Fe, Cl, B
‑ What is buffering capacity?
ability of material or solution to resist changes in pH
‑ What is the difference in the active vs slow vs passive pools of soil organic matter?
active - BM,POM, NH sub, soil organsms eat, days to years, mineralizable N, slow - fine POM, high lgnin, deacdes, some N. passive - humus, 100s-1000s years, stable CEC, holds water, slow loss
‑ What are the three major pools of soil acidity?
active acidity, exchaneable acidity, residual acidity
‑ How does temperature vary throughout the composting process?
active phase - 55-70C, curing phase - drop 37C
‑ How can you increase soil pH? How can you decrease soil pH?
adding protons to increase adding bases to decrease
‑ Does organic matter decompose faster via aerobic or anaerobic decomposition?
aerobic decomposition is faster
‑ Should compost piles be anaerobic or aerobic? How is this accomplished?
aerobic, accomplished by frequent movement of the compost pile for aeration
‑ What are the most numerous soil organisms? What soil organisms have the highest biomass?
bacteria are most present, while earthworms and fungi are the highest in biomass
‑ What is biomass vs detritus vs humus?
biomass - living organisms, dteritus - identifable dead tissue, humus -nonliving nontissue
Mg 2+
chlorophyll and photosynthesis
‑ What is calcareous?
contains calcium carbonate that visibly interacts
‑ What colors generally indicate high amounts of carbon in the soil?
dark color means high amounst of carbon is soil
‑ What are some properties of humus?
dark color, heterogeneous, collodial, modified lignin
‑ What is the field technique for identifying calcareous soils?
droping acid
‑ How are earthworm casts different vs the original soil?
earhworms shred and mix om while casts hold aggregates to protect om
‑ What are practices that promote losses of organic matter in soils?
erosion, tillage, plant removal, overgrazing
‑ What is ESP? How is ESP calculated?
exchangeable soidum/ total CEC x 100
‑ What types of environmental conditions are preferred by microbes in general, such as oxygen levels, moisture, temperature, pH, nutrients, etc?
extereme temperatures, exchangable Ca and moderate pH, and oxygen depending on whats present
‑ What are mycorrhizae? What is the difference in ecto- vs. endo- mycorrhizae?
fungus-root, ecto- outside, endo- inside the root cortex
‑ What is meant by the term "redox" and what is the general chemical reaction for it in soils?
gain/loss of e- through oxidation and reduction
‑ What are practices that promote gains of organic matter in soils?
gen manure, return plant residue, low temperature and shading
‑ What is the procedure for collecting soil samples?
go around gather multiple samples for the same plot or area and combine those sameples, different plots/areas are kept separate
‑ Why is macroporosity of potting media important? Do you generally want low or high macroporosity?
high macroporosity for proper draining and prevent prolonged water holding
‑ How can you keep your worms happy?
high om and moisture low saturation
‑ Why is Al3+ considered an acid cation?
hydrolysis of Al3 produces H
‑ What unique properties do sodic soils have?
hydrolysis of sodium carbonate
Ca2+
in cell walls
‑ What is the relationship of soil carbon with depth below the surface?
increase in depth decrease in carbon
‑ How does tillage/plowing affect soil organic carbon content?
increase in tillage decrease carbon
‑ What are the problems with too low of soil pH?
inhibits root formation and microbial processes
Calculate pH
inverse log[H]
‑ How can increased temperatures generated during composting be beneficial?
kills pathogens, eliminated weeds, breaks down phytotoxic compounds
‑ How is immobilization of nitrogen affected by the C/N ratio of organic additions to soils?
leads to N deficiency in plants
‑ Why do areas with high rainfall have low pH?
leeching base cations and more carbonic acid formation
‑ Why don't most fertilizers contain Mg and Ca?
limeston is available for Ca and Mg
‑ What are some common products used to decrease pH?
liming with oxide and hydroxide
‑ What are the problems with too high of soil pH?
locks nutrients and restricts bioavilable nutrients
‑ What is the difference in soil macro-, meso-, and micro- organisms? What are some examples of each?
macro >2mm, meso 0.1-2, Micro <0.1
‑ What are the different aeration process in soils (i.e. how do gases move)?
mass flow, diffusion, air filled porosity
‑ What is soil salinity and how is it measured? What are the common units?
measured via electric. Conductivity in dS/M
‑ What kinds of reactions does sulfur undergo in soils?
mineralization into SO42, oxidation, immobilization, reduction, solution
‑ Are micronutrients generally more soluble at high or low soil pH?
moresoluble at a low pH
‑ Are most soils low or high in phosphorus?
most soils are low in P
‑ What is the general chemical reaction for decomposition in soils?
organic compound and 2O2 -> CO2 and H2O and energy
‑ What is chelation?
organic compounds with 2 or more atoms capable of bonding cationic micronutrients
‑ What is compost?
organic residue that is pilled and moisten to undergo aerobic deomposition
‑ Why is pH an important part of soil testing?
pH detects plant available nutrients and soil interaction
‑ What is the difference in pH vs. base saturation?
pH measures cations and base saturation is how mush base is present?
‑ What ingredients would make a good standard potting mix for most all-purpose mixes?
peatmoss, vermiculite, perlite/sand
‑ Why is soil temperature important and what processes does it affect?
plant processes, microbial processes, soil structure, erosion, frost heaving, permafrost
‑ In which types of climates do these soils occur?
rangelands, dryland farming, irrigated agriculture
‑ What is meant by the term C/N ratio?
ration between C to N
‑ What is Eh?
redox potential measures how aerobic or anaerobic the system is
‑ How does buffering capacity vary for sandy vs clayey soils?
sandy is lower while clayey soils are higher
‑ What are some materials that have Low macroporosity?
silt, clay, peat, compost, manure
‑ How does lignin content affect decomposition of plant residues?
slows decomposition
‑ What are the proper reclamation steps for saline vs sodic vs saline-sodic soils?
sodic - gypsium and soluble salt, saline -irrigation water with low SAR and good drainage , saline-sodic -gypsium and soluble salt with excess clean irrigation water
How can you moderate surface soil temperatures?
soil mulches
‑ Why are microbiotic soil crusts important in dry/desert soil environments?
stabilizes the soil surface and sequeser, mutualistic algae fungi mosses bactera etc
‑ What is the best initial C/N ratio for a compost mixture before beginning the composting process?
start 30:1 move to 10-20:1
‑ Why aren't potting mixes made of 100% peat moss?
too acidic for organic material
‑ Is phosphorus mostly soluble/mobile or insoluble/immobile is soils?
very insoluble and immoble
‑ What types of parameters are generally analyzed for a soil test?
water pH, buffer pH for lime, PK MG CA by Mehlich, lime and fertilizer recommendation
‑ What conditions promote the decomposition of organic matter in soils?
wet soil leads to less O2 and decomposition
‑ What is the rhizosphere and how is it different than the surrounding soil?
zone around the active root that has a higher concentration of mcirobial populations
