Final Flashcards
Organic matter is responsible for ___ of CEC. It ______ soil aggregates, and increases __ ___ ____. Energy, Carbon and nutrients for _______
1/3
stabilizes
water holding capacity
biomass.
Soil organic matter can be divided into 3 components:
Biomass- living organisms
Detritus- Identifiable dead tissue
Humus- nonliving,non tissue
a complex mixture of brown and black amorphous and colloidal organic substances that result from microbial decomposition and synthesis and has a chemical and physical properties of great significance to soils and plants.
Humus
What percent of carbon is lost to CO2 from organic residues breaking down?
60-80
Humic acids-
Dark brown to black, high molecular wt.
Soulble in bases, not acids.MW up to 300000 g/mol
Fulvic acids-
Yellow to red, lower molecular wt.
Soluble in base and acid. Mw 2000- 30,000 g/mol
Humin-
Highly condensed completed with clays.
Insoluable
Non humic substances make up what percent of soil organic matter? they are (more or less) complex chemically? (More or less) resistant to decomposition? The chemical and physical structure is _______?
20-30
Less
Less
Definite
Humic substances make up what percent of soil organic matter? they are _____. they are _____ in color and have a _____ molecular weight? _____ resistant to microbial attack?
60-80
amorphous
Dark, High
highly
Organic matter soil physical properties-(4)
Dark brown to black surface horizons
Improved soil aggregation
increased water infiltration
Increased water holding capacity
CEC,______ accounts for 50-90% of CEC in surface soils. and provides much of the ______________ in soils.
Humus
pH buffering capacity
Organic Matter(3)
provides most of the food for heterotrophic soil organism, especiall for the detritus fraction.
Provides nutrients for plants.
Diversity of organic matter increases diversity of soil organisms.
Soil organic matter increases or decreases depending on balance between?
Where do the gains come from?
Where do the losses come from?
gains and losses of carbon.
Gains- from plant residues grown in place or applied organic matter
Losses- from respiration, plant removal, and erosion.
How does temperature influence amount of organic matter?
at low temps, plant growth is greater than decomposition, organic matter accumulates.
How does moisture influence amount of organic matter?
more moisture means more organic matter
How does vegetation influence amount of organic matter?
more organic matter under grassland than forest
How does Soil texture influence amount of organic matter?
more organic matter in finer textured soils.
How does drainage influence amount of organic matter?
poorly drained soils accumulate more organic matter.
How does Tillage influence amount of organic matter?
decreases organic matter. aerates soil and breaks up residue
Guidelines for managing SOM(5)
add continuous supply of plant residues, animal manuers.
Ideal amount of SOM depends on soil, plants, and climate.
Adequate nitrogen
Limit tillage
Encourage perennial vegetation
Soil microorganisms need N in addition to C.
1g of N for every 24g of C
If C/N ratio exceeds 25:1 what happens
Microbes will need to get N from soil
Plants could suffer from N deficiency
Decay of organic matter could be delayed.
Composting-
creating humus-like organic materials by aerobic decomposition outside the soil.
Compost-
Organic residues have been allowed to undergo biological decomposition.
Thermophilic Compostion-
Composting in large aerated piles; heat builds up within the compost piles.
3 stages of thermophillic compostion-
- Mesophillic stage-
- Thermophillic stage.
- curing or 2nd mesophillic stage.
Mesophillic stage-
sugars and readily available food is metabolized; temps to voer 40C
Thermophillic Stage-
decomposition of cellulose and other resistant materials; 50-70C
Curing or Second mesophillic stage-
temp falls to near ambient levels
When compostion the C/N ratio will decrease until what ratio is reached?
10:1 -20:1
Cocomposting-
mixing organic materials to try to balance initial C/N ratios.
Advantages of Compost-(3)
Nitrate depression occurs in compost pile; wont affect plants
Composts can suppress soil borne plant diseases
Compost is carbon -neutral; environmentally sustainable
Carbon,Hydrogen, and Oxygen-
Non mineral nutrients
from water and CO2
plant backbone
Carbohydrates
N,P,K
primary macro nutrients
S,MG, Ca
secondary macro
Nitrogen is obtained from?
Whats it found in?
Organic matter Biological fixation Chemical Fixation. Proteins Nucleic acids Enzymes.
Nitrogen Fixation-
converts N2 gas to NH3
Nitrogen Volatilization-
gaseous loss of N to atmoshpere (NH3)
Nitrification-
NH4– NO2—NO3
nitrosomonas and Nitrobacter
Leaching-
loss of soluble N drainage water.
Denitrification-
loss of N back to the atmosphere
Biological Nitrogen fixation-
Most important reaction for life
2/3 of N fixed
Symbiotic fixation in rhizobium and legumes
Biological Nitrogen fixation-
Most important reaction for life
2/3 of N fixed
Symbiotic fixation in rhizobium and legumes
Nonsymbiotic- source of N for native species.
Mineralization-
Conversion of organic compounds to inorganic compounds.
immobilization-
plant or microbial uptake.
phosphorus-
obtained from-
Found in plants as:
P
organic matter, fertilizerrs
ATP, respiration and photosynthesis, drives biochemical processes.
P problem for soil fertility-(3)
Total P in soil is 1/10 that of N
P in soil is unavailable
when added to soil it becomes fixed to Fe and Al oxide surfaces.
Ways to control P availability:
Saturate P fixation capacity Fert. placement Combination of Ferts P efficient plants Manuers Contol pH Encourage mycorrhizal symbiosis
Eutrophication in lakes
Natural process based on nutrient availability
occurs when excess nutrients are added to a system
characterized by algal blooms
often due to excess N and P in systems
Eutrophication in lakes(4)
Natural process based on nutrient availability
occurs when excess nutrients are added to a system
characterized by algal blooms
often due to excess N and P in systems
Potassium-
mostly influenced by cation exchange 2:1 clays readily fix it Illite filled with K+ enzyme activator Osmotic regulator
Sulfur-
Amino acids, Vitamins, Aromatic oils
Ca and Mg-
Chlorophyll and cell walls. Limestone
Cations Iron- Zinc- Nickle- Copper- Manganese
reduction reactions seed development seed devel respiration metabolism
Anions
Molybdenum-
Boron-
Chlorine-
Nitrogen fixation
Enzymes and cell division
Photosynthesis and root growth
Chelates-
keep cations in solution
orgainc compunds with 2 or more atoms
synthesized by plant roots
Deficiency-
very low levels of a nutrient;plant growth restricted
Toxicity-
high levels of a nutrient; plant will take up to much.
4 goals of nutrient management-
- Cost effective crop and animal production
- efficient use and conservation of nutrient resources.
- Maintenance or enhancement of soil quality
- protection of environment.
Factors influencing fertilizer use-(5)
crops- legumes , grasses
Soil- natural fertility; physical limitations
Climate- humid regions need more fert.
Economics- yield increases follow a curve
Management-personal preferences
Soil sampling and testing-
best time is at end of growing season
separate samples needed for each soil type
random samples
avoid unusual areas
Site- specific nutrient management-
Precision farming
combines technology from GPS and GIS
Geologic erosion-
is a natural process that transforms soil into sediment.
depends on rainfall
under ideal conditions rate of formation equals rater of erosion
acceleratied erosion can be 10-100 times greater than geologic erosion.
On-site effects of accelerated erosion-
Soil loss- 0.5 tons/A/yr forests, 40-140 tons/A/ yr rotated crops.
Plant nutrient loss- fert and organic matter loss.
texture change-sand often left behind
structure change- block pores
field dissection- gullies
Off site effects of accelerated erosion-
Engineering structure damage- roads/bridges
Water pollution- non-point sources
Sedimentation- turbidity, loss of navigation ability
Health Hazard- wind erosion
Rill erosion-
water collects in depressions and breaks through forming small channels rills can be removed by tillage.
Splash erosion-
impact of a rain drop can move soil 1-2 ft in air and 3-5 ft away.
Sheet erosion-
soil is removed uniformly from every part of the slope, not very noticeable.
Gully erosion-
Severe soil removal. Cannot be removed by cultivation.
A= R= K= L= S= C= P=
estimated annual soil loss runoff factor soil erodibility factor Length slope cover and management factor supporting practices factor.
Why tillage?
seed bed prep,
weed control
Looks
Tradition
Conservation tillage-(4)
any practice that leaves 30% cover over the soil
incorporates residue leaving a bare surface
no-till uses herbicides to kill vegitation with minimal soil distribution
ex) ridge tillage,stubble mulch, strip till,
History of No-till-
first in 1960s
milan,Tn Tom mcCutchen
Limitations are equipment and herbicides.
No till-
a method of farming where the soil is left undisturbed from the harvest of the crop to the planting of another.
Crops are planted directly into the residue from the previous crop.
Why no-till?(12)
improved water inflitration increased soil organic matter decreased soil compaction improved soil tilth increased wildlife food and habitat reduced air pollution reduced labor saves time field accessibility lower machinary requirements reduced operation costs reduced soil erosion
What 3 things ring successful no till reqs.
- positive attitude
- Proper planting equiptment
- Proper herbicide program
No-till weed control
Burndown herbicides
Selective preemergence
Selective post emergence herbicides.
Vertisols
Soil order in which soils have a high content of shrink-swell clays and have deep cracks when dry.
Histosols
Soil order in which soils have more than 30% organic matter.
Entisols
Soil order in which soils are composed of very young soils with no B horizons
Andisols
Soil order in which soils are formed from volcanic ash and lava deposits.
Oxidation
weathering that involves the loss of electrons and/or transfer of electrons.
Hydrolysis
Weathering which involves H20 molecules are split and the H+ ions attack the crystal surfaces.
Eluvial horizon-
Zone of loss, loss of silicate clay, Fe and Al; E horizon
Illuvial Horizon-
Zone of accumulation; accumulation of Fe and clay that results in enhanced structure; B horizon
Leaching-
the removal of minerals in solution from the soil by downward movement of water.
Loess-
Wind blown parent material deposited during periods of glaciation; commonly found in much of west tennessee
Residuum-
Parent material formed in place from rocks and minerals; found in the centeral basin. of tennessee.
Epipedon-
A diagnostic surface horizon of soil.
The composition of ideal soil?
25% water
25%AIR
5%organic
45% mineral
A soil particle that is 1mm in diameter is ?
Sand
At permenant wilting point what is the water potential of the soil?
-1500 kPa
Alluvium-
Unconsolidated material deposited or in transit by streams, including gravel, sand ,silt clay,
Weathering in which CO2 combines with water,creating an acid that helps to break down rocks and minerals
Carbonation
Soil profile-
A vertical section of the soil through all its horizontal layers .
What force prevents the rapid downward movement of water through the silt loam?
Capillary forces.
What does the munsell system use to describe soil colors?
Hue, Value, and Chroma
What causes the adhesive and cohesive properties of water?
Hydrogen Bonding
When determining soil texture by feel, a smooth feel indicates a high percentage of?
Silt
In lab we dipped soil peds in wax to determine their?
Bulk density
The unconsolidated mineral and organic materials on the immediate surface of the earth that serves as a natural medium from the growth of plants?
Soil
What are 3 functions of soil?
modifier of the atmosphere
Habitat for soil born organisms
Engineering medium
What are the 3 classes of rock?
Igneous
metamorphic
Sedementary
What are negative effects of poor aeration?
Lack of oxygen for plant roots
Accumulation of organic acids
Decreased uptake of plant nutrients
Kaolinite-
clay with a 1:1 structure.
What ion can replace silicon in the silicon tetrahedron structure of clay minerals?
Aluminum
As the pH decreases from neutral,what happens to the availability of calcium and magnesium in the soil?
the availability of both decreases.
What is an Acid?
A compound that decreases the pH
A compound that donates protons
A compound that reacts with a base to form water and a salt.
In the aluminum octrahedron structure of clay minerals, how many hydroxide ions surround the Al?
6
Hydrogen ions and aluminum ions that are found on the cation exchange sites are considered to be part of?
Reserve acidity
A type of fungi that forms a symbiotic association with roots of higher plants.
Mycorrhizae
What is a liming agent?
they all have OXYGENS in them
The zone of soil that immediately surrounds the root is called?
The rhizosphere
What can be used to increase the soil temperature?
Dark colored or clear plastic mulch
Infiltration-
Absorption of water by the soil; movement of water into soil.
Respiration-
C6H12O6+ 6O2 = 6CO2 +6H20
Actinomycetes-
group of filamentous bacteria that are often branched
Fungi-
Group of organisms responsible for most soil-borne diseases.
Transpiration-
Evaporation of water from leaves
Nematodes-
Microscopic thread worms or eelworms
Protozoa-
Mobile single -celled creatures that capture and engulf their food.
Percolation-
Downward movement of water through soil
Photosynthesis-
6 CO2 +6 H2O = C6H12O6 +6O2
Water table-
The upper surface of groundwater
Hyphae-
Individual fungal filaments
Redoxymorphic features-
Soil properties associated with wetness that result from reduction and oxidation of iron and manganese compounds.
Name 3 ways earthworms benefit the soil:
produce casts-high in nutrients aerate the soil provide drainage to the soil size and stability of aggregates assist in notill opperations
What are the Basic soil elements?
Ca,Mg,Na,K
what are the non basic soil elements?
H+, Al
Why is kaolinite good for building as a foundation?
It is a small particle and can be packed together tighter, since its only 1:1. Also it doesnt expand. It is also not reactive so it wont deteriorate over time.
What is a perc test\?
A test to measure how well the water percolates into the soil over time. Its used for septic tank fertilization fields.
