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