Exam 2: Study Guides Flashcards
which is greater? the CEC of clay or CEC of organic matter?
organic matter
what factors determine how much organic matter is maintained in mineral soil?
a. Fresh organic residues
b. Active and unstable decomposing matter
c. Living organic matter
d. Stable organic matter
what makes up the organic matter portion of the soil?
- composed of carbon
- living fraction
- dead/decomposing fraction
biological functions of SOM
i. Source of energy
ii. Reservoir of nutrients
iii. Soil/plant system reliance
chemical function of SOM
i. Cation exchange capacity
ii. Binding of SOM to soil minerals
iii. Soil pH
physical function of SOM
i. Structure stability
ii. Water retention
iii. Thermal property
list at least 3 reason organic matter is important to sandy florida soils
- bind soil particles together and create soil structure
- prevent draining
- increase CEC
what is decomposition?
- SOM at different forms of decay are food for microbes
a. Soil organic matter microbes are responsible for the formation of organic matter through decomposition
b. Decay serves as food for microbes
c. Reservoir of energy
d. Mass loss
e. Break carbon bonds and produce carbon dioxide
describe the process of decomposition in terms of inputs and outputs within the carbon cycle
a. Photosynthesis converts carbon dioxide to sugars into a useable form of energy
b. When plant biomass dies, most of the solid carbon is put back into the atmosphere as CO2 and a small amount is stored as soil organic matter
c. Photosynthesis converts gas into a solid – sugar
i. Sugar provides energy to plants and other biomass
d. Dead leaves contain sugars and other energy
e. Plant roots respire which uses the sugar used and burns energy from sugars
what does Dr. Enloe call decomposition “reverse photosynthesis”? Explain using the terms carbon dioxide, energy, microbial activity
c. Sugars are carbon-carbon bonds in plants. When a plant dies, that energy and CO2 that is stored in the plant is released
d. Additionally, the organic matter is also used as a source of energy in microbial growth
i. Food for microbes and other decomposers like earthworms
what is compost?
a. The biological decomposition of organic constituents under controlled conditions to form a stable, humus-like product
what does stabilized mean in terms of the composting process?
a. Biological and chemical decomposition of the wastes has ceased or diminished to a level so that such decomposition no longer poses a pollution, health, or safety hazard
b. biological decomposition of the waste that was composed or anaerobically digested has occurred to a sufficient degree that will allow beneficial use
c. Based through the thermophilic stage
list the composting parameters that can be controlled in a successful process. identify how these parameters are optimized in the composting process.
a. Carbon to nitrogen ratio
i. Composting occurs most easily if high nitrogen and carbon materials used with the ratio being 25-40 parts carbon for 1 part nitrogen
b. Distribution of particle sizes in the pile
i. Mix of course and fine particles
ii. Create macropores for greater airflow in the pile
iii. Micropores allow for microbial activity
c. Moisture content
i. 40-60%
ii. Too little – mold growth
iii. Too much – anaerobic conditions
d. Oxygen content
i. 15% of O2 to reduce anaerobic activity which cause compost to smell
e. Temperature
i. 90 – 140 F
ii. 60- 140 F
how are pathogens killed in the composting process?
a. Fungi replace bacteria in phase 2
b. The fungi in phase 2 are replaced by filamentous bacteria and mold in phase 3
c. In phase 4, worms and invertebrates feed upon the bacteria from the previous phase
d. High temperatures kill pathogens
list 2 ways that composting and anaerobic digestion are similar
a. Decomposition of organic products
b. Stabilizes the organic fraction into a material that can easily and safely be stored, handled, and used in an environmentally acceptable manner
list 2 ways that composting and anaerobic digestion are different
a. Composting is under aerobic conditions
b. Anaerobic digestion is done under anaerobic conditions
identify the pools and fluxes in the nitrogen/phosphorous cycle for a natural ecosystem
i. Nitrogen comes from the soil - small amount of organic matter and clays that contain nitrogen. phosphorous comes from erosion of minerals.
ii. Limit plant growth because nutrients are low
iii. Tightly cycled to meet plant immediate needs
iv. Additions are small but losses are small
v. Met through decomposition and mineralization
identify the pools and fluxes in the nitrogen/phosphorus cycle for agro-ecosystems?
i. Nitrogen/phosphorus is added into the environment through fertilizers
ii. Additions are greater and losses are greater
iii. Internal transformations cannot meet a crop’s daily nutrient needs without the additions of fertilizers
for the N and P cycle, identify individual processes that require microbes
nitrogen:
i. NH3 – ammonia – nitrogenase breaks N2 triple bond
ii. Nitrifying bacteria can make nitrate NO3 – and nitrites NO2 –
iii. Denitrifying bacteria – nitrate reductase back into N2 for the atmosphere
phosphorus:
i. Lithotrophs but most phosphates are made from erosion
ii. Decomposers break is down and re-release it back into the cycle
explain the role of decomposition in plant nutrition and soil organic matter formation
a. Legumes are known to host rhizobium bacteria in roots
b. The legumes and bacteria die and the leftover is mineralized and nitrified
c. In a form the plant can take up
d. Biological fixation followed by mineralization
e. Can also form nitrogen gas through denitrification
mineralization and immobilization as components as components within the decomposition or organic materials and the supply of nutrients to plants
predict whether mineralization or immobilization occurs based on the C to N ratio of a crop residue
c. High N content/low C content – mineralization dominates
d. Low N content/low C content – immobilization dominates
the role of pH and lime in phosphorous management
a. Phosphorous is very soluble t neutral pH – optimal uptake
b. Acidic soil – low pH
i. High in aluminum or ion
ii. Phosphate sticks to these minerals and sticks to the soil particles
c. Basic
i. More calcium
ii. Form calcium phosphate and insoluble and forms a solid
Adding lime (Figure 1) increases soil pH (reduces acidity), adds calcium (Ca) and/or magnesium (Mg), and reduces the solubility of Al and Mn in the soil.
