Test 2 Flashcards
Percent of water that’s ocean water.
Ice?
all other water?
ground water?
97.25%
2%
<0.05%
0.7%
percent lake water?
Soil moisture?
Atmosphere?
Rivers
60%
33%
6%
1%
What are two restrictions of water movement?
Rate of water supply from soil to root.
Rate of loss from leaves through evaporation.
Evapotranspiration is affected by?(5)
Radiant energy- 540 calories to evaporate 1g water. Atmospheric vapor pressure Temperature wind soil moisture supply
Different crops lose moisture at different rates(T/F)
True
Transpiration ratio-
kg of water needed to produce 1kg of dry weight.
Water vapor losses from soil surface and plants are determined by(4)
Climate
Plant cover
Water use efficiency
Length and season of plant growing period
Ways to control soil evaporation?
Encourage soil cover
Mulches
Paper plastic mulches- high cost/high value crops
crop residue and conservation tillage- requires herbicide use.
Percolation-
subsurface drainage, downward movement of water through soil.
-loss of soluable salts
runoff-
surface drainage
Leaching losses
loss of fertilizer
soil and water pollution
problems abated through split applications of fertilizers.
infiltration-
absorption of water by soil
If rate of rainfall exceeds rate of infiltration what happens?
soil ponding or surface runoff occurs.
Land drainage occurs in what two regions?
Delta and flat coastal plains.
Ex. of subsurface drains?(3)
Mole drain-lasts one season
Perforated plastic pipe- 90% of todays systems
Clay tile drains- to expensive for ag. popular 20-30 years.
Benefits of drainage?(5)
reduces frost brewing helps soils warm up faster in spring Aeration easier to work fields Maintains productivity of irrigated soils.(no salting out)
Perc test is used for what? how do you do one?
to determine percolation test. and determine solubility for a septic tank drainfield.
measure water in a hole over time.
Aeration-
process of maintaining a supply of O2 to the soil
Oxygen is important why?
respiration
organic matter decay
release organic nutrients(N,F,S)
reducing toxicities of elements( Mn and S)
Diffusion-
random motion of molecules from an area of high concentration to an area of low concentration.
Partial pressure-
the pressure a gas would exert if it alone were present in volume occupied by a mix.
Factors affecting diffusion-
Texture-
Structure-
Water Content-
Texture-
finer textures soils have more micropores
Structure-
introduces large pores into fine textured materials.
Water Content-
drainage of macropores, oxygen diffuses more slowly through water than air.
Consequences of poor aeration(5)
reduces microbial activity Accumulation of organic acids Plant growth curtailed Absorption of nutrients and water is decreased Toxic compounds
Poor aeration-
if air filled porosity <20% plants will suffer from deterioration of roots.
Wetlands-
Soils that are water-saturated near the surface for long periods of time. Plants and microbes can grow and remove oxygen.
The weter end of a wet land is where?
where water is to deep for rooted emergent vegetation.
Wetland Delineation-
the drier end of wetland.
3 characteristics of a wetland-
Wetland hydrology, Hydric soils, Hydrophytic plants
Hydric soils-
soils subjected to periods of saturation
Soil temperature influences:
Microorganisms- o matter, decomposition
Plants- germination, nutrient uptake,transpiration/respiration.
Mineral weathering
Reflectance by clouds- absorbence by dust and water- Evaporation- Radiation- Reflection-
30% 20% 30% 5% 5%
what 10% of sun is absorbed by the soil?
10%
factors that affect energy entering the soil?
soil color
slope- closer to perpendicular the greater the absorption
Vegetation
Daily temperature fluctuations are greatest at the soil surface and decrease with debth.(T/F)
true.
How can you modify soil temp?
Moisture/Drainage
Mulches(color)
What is the smallest soil particle?
Clay 1um, highly reactive w/ large surface area per unit mass.
CEC-
ions are absorbed on the colloid surfaces.
Mineral properties-(2)
Composition-kinds of atoms
Crystallinity- arrangement
clays are composed of two basic crystal units:
Tetrahedrons
Octahedrons
Interlocking units of Aluminum Octrahedron form what?
an octrahedral sheet.
what is an isomorphic substitution?
substitution of an ion of similar size for Si or Al that occur during crystal formations. has charge imbalance but isnt negative.
1:1 Clay minerals are made of?
1 tetrahedral sheet and 1octohedral sheet, share oxygen atoms. H-bonds
2:1 Clay minerals are made of?
1 octohedral and 2 tetrahedral sheets, share oxygen linked sheets.
Kandites
1:1 Clay mineral
CEC 2-10 cmolc low reactivity
broken edges, non explanding.
Smectite-
2:1
CEC 80-120 cmolc
highly reactive, explanding, high surface area
illite-
2:1
CEC is 20-40 medium
vermiculite-
similar to illite
CEC 120-150,limited expanding,high surface area.
Chlorite-
2:1:1
CEC 20-40, medium ,increased strength of bonding.
other sources of charges in soil:(3)
Exposed crystal edges
Fe and Al oxides
Humus
Cations-
positively charged ions
Clays-
negativly charge
Cation adsorption-
electrostatic attraction, not readily leached
Cation exchange-
replacement of one cation for another on the exchange site.
CEC definition-
ability of soil to hold and exchange cations, measure of the basic fertility status of the soil
Mole-
6.02x10^23 ions, mass of 1 mole of an ion
equivalent-
quantity of an ion that will supply the same total charge as 1 mole of H+
Predominant cations
Ca+2 Mg+2 H+ Na+ K+ Al+3
factors influencing exchange reactions-(4)
Concentration of ions
Number of charges on ions
Hydrated radius of ions
pH
pH-
master variable that affects many soil chemical and biological properties.
Why is pH important?
Availability of nutrients
plant species that will grow
Activity of soil microorganisms
Mobility and breakdown of pollutants
An Acid donates what? and A base excepts what?
protons(H+) and a Base accepts the proton(H+)
What is the end result of an acid and base combining?
formation of water and a salt.
pH is the unit of measure for what?
acidity and alkalinity
Buffer-
a substance that has the ability to resist changes in pH, acts as a reserve and soil systems are natural buffers.
Soil solution(Active Acidity)-
1 of every 10,000 exchangable cations are in active phase. less than 1 lb/acre of lime needed to neutralize.
Soil Colloids”reserve acidity”-
2-8 tons /acre needed to neutralize .
Salt replacable(exchangable) acidity-
involves Al and H that are easily exchangeable by other cations in a simple unbuffered salt solution.
Residual Activity-
Can be neutralized by limestone or other alkaline materials but cannot be detected by the salt- replaceable technique.
How do soil become acidic?
Leaching of bases by water
Crop removal of bases
Acid forming fertilizers
Effects of soil pH on plant growth:(4)
Nutrient avalibility
Solubulity of toxic substances
effects on microorganisms
Direct effect of pH on root cells
Percents of base saturation 6.5-7:
5.5-6.5:
low-5.5:
80% and up
50-80%|
less than 50%
Liming soils:
raises pH and eliminates nutrient toxicities, deficiences and microbial activity. soils respond to lime after the pH drops below 6.0
Soil amendment-
anything added to the soil that improves soil chemistry without providing nutrition. ex.(lime)
How does lime work?
it breaks down Ca ions and Carbonic acid.neutralizing acidity.
Limiting agents:
CaO
Ca(OH)2
CaCO3
MgCO3
Application of lime-
every 3 -5 years
applied with or before the crop
not economical to apply >6tons/acre/year
Amount based on soils buffering capacity
Limestone quality depend on?
the neutralization value and fitness of grind, limstone quality is the product of the neutraliztion value and the fitness factor.
Fitness Factor-
depends on how finely the rock material is ground. smaller particles the more reactive,
Quality factor-
Neutralizing value X fitness factor
Acid rain-
Acid decomposition from the atmosphere. Nitrogen and sulfur containing gases. mostly a problem in humid forests near urbanized and industrialized areas.
How to reduce the effects of acid rain(3)
reduce S and N emissions
liming lakes and forests is economically limited
re-vegetation.
What is capable of acting as a habitat for biological organisms?
Soil
What is responsible for most of the chemistry that occurs in soil?
Soil organisms
Photosynthesis
6CO2+6H2O =C6H12O6 +O2
Respiration
C6H12O6+6O2=6CO2+6H2O
Soil macro and micro organisms are important for:(4)
Organic matter decomposition
Nutrient availability
Soil development
Plant disease
Prokaryotes:
Bacteria
How do large animals help soil develop-
enhance soil by burrowing and mixing soil
Earthworms
Annelida
excret casts
increase aeration and drainage
increase size and stability of soil aggregates
mixing is very important in no till system
Protozoa
most varied and numberous
cause animal and human disease
predators in the rhizosphere
Nematodes-
Microscopic thread worms or eelworms
Saprophytes-
organisms that live on decaying matter
Parasites-
infest roots causeing extensive damage to field and vegetable crops
predators-
prey on other microbes
Green plants-(3)
Vascular plant,
contribute to soil more than other living organisms combined
autotrophs
Soil benefits of plants-(4)
Organic matter produced when plants decompose
Root channels influence physical properties
Nutrient uptake influences soil chemistry
root decomposes influences soil organisms
roots-(rhizoshpere)
tiny channels are increased in size as roots swell and grow, 15-40% mass of above ground biomass.
rhizosphere contributes to:(4)
organic acids
amino acids and simple sugars
Mucigel
competition for resources.
Algae-
photosynthetic,aerobic photoautotrophs.
needs oxygen light and moisture.
Fungi-
Aerobic heterotrophs, humus formation
need oxygen and organic carbon
responsible for most soil born diseases
Molds-
organisms of threadlike mats formed from individual strands, break down anything, low pH
Mycorrhizae-
symbiotic mold fungi,
fungus root symbiosis obtain c energy from roots,
act as root hairs
help supply nutrients to root.
Ectomycorrhizae-
external, doesn not penetrate the cortex cell walls of the root.
Endomycorrhizae-
enter cells
Actinomycetes-
resemble molds, like pH OF 6.5-7,
Can break down complex substances.
Bacteria-
smallest organisms,
most diversity
unicellular form colonies or spores
Autotrophs-
C form CO2 ,inorganic
Heterotrophs-
C and energy from .
most bacteria.(ultimate decomposers)
injurious effects of soil organisms:
rodents eat roots
everything else eats plants
soil born diseases, most from fungi
Controls of plant diseases:(6)
Quarantine Eliminate crop host Crop rotation or tillage pH control Steam and chemical sterilization Plant breeding
Agriculture practices that decrease diversity:(5)
pesticides erosion monocultures excess tillage industrial sewage
Aig practices that increase diversity:(5)
Drainage and aeration Fert and lime manures balanced irrigation Erosion control
