Module 6 Flashcards
how do you improve soil quality and promote environmental quality?
incorporating organic matter into soils
what does organic residues on soil surface protect the soil from?
erosion and compaction
what happens when soil organic matter is decomposed and incorporated within the mineral soil?
- improves soil quality by promoting soil structure and increasing water infiltration
what is soil organic matter composed of?
- primarily carbon
- exists in a continuum of decay
what is responsible for soil organic matter formation?
soil microorganisms
- serves as food for microorganisms
defining features of the A horizon
soil organic matter
- dark and brown in color
how much organic matter can the surface layer of soil contain? what is typical of mineral soils?
- 20%
- 1 - 5%
in what ways can soil organic matter change the property of soils?
- soil color, CEC, and water holding capacity
If we are adding organic matter to soils to improve soil quality, what should be our target amount?
As a rule of thumb, we target 5% soil organic matter in the top 6 to 12 inches of the soil A horizon.
However, sandy Florida soils are an exception to the rule. Soil organic matter has a high surface area, and is sometimes referred to the glue necessary to bind soil particles together and create soil structure
organic soils
histosols
- found in south florida and in everglades
a small fraction of soil organic matter is composed of living animals, what are they?
earthworms, mites, nematodes, and soil microbes
-how much of non-living organic matter is composed of decomposing organic material?
around 15%
- the material is more uniform in appearance and it’s darker in color than the original fresh residues
- considered active and unstable
what do we mean when organic matter is unstable?
- losing mass rapidly though decomposition and still undergoing constant changes in its chemical structure
what is decomposition?
mass loss
what happens as microbes decompose organic matter?
they break carbon bonds and produce carbon dioxide
what drives mass loss?
carbon dioxide
how much of the carbon stored within the soil is stored in a stable fraction?
65%
how does soil organic matter improve soil quality for crop production?
changes in the biological, chemical, and physical composition
the more diverse the biological community…
the more resilient it is to disease, stress, and disturbance
how can SOM improve soil structure?
- cause it to clump and form soil aggregates
- With better soil structure, infiltration increases and improves and the soil’s ability totake up and hold water increases
organic matter can absorb and hold how much of its weight in water?
90%
what is a major storer of global carbon?
soil
the carbon cycle moves carbon between what?
the atmosphere, vegetation, soil, and then back to the atmosphere
decomposition
the flux that moves carbon from the vegetation to the atmosphere as CO2 and to the soil as organic matter
what is the most important flux of the carbon cycle?
photosynthesis
the carbon cycle not only moves carbon but also what?
the movement of energy that is required for life above and below ground. The source of energy is the sun, and the sun’s energy is stored in the carbon to carbon bonds and plant biomass, and soil organic matter.
flux of photosynthesis
- converts gas to CO2 into a solid - sugar
- stores energy from the sun within the carbon-carbon bonds of sugar
how is photosynthesis measured in the field?
measure how much weight or mass a plant has put on within the time frame of one year
reverse photosynthesis
respiration and decomposition
what are some ways carbon is released back into the atmosphere?
- use sugars fixed by leaves during photosynthesis
- decomposition
at what temps is microbial activity higher?
warmer temperatures
what conditions slow decomp?
saturated conditions
why is decomposition incomplete?
- not all biomass is sugar
- not all organic biomass is transferred to CO2
composting
the biological decomposition of organic constituents under
controlled conditions to form a stable humus-like product. The process occurs quickly as the
conditions for microbial activity are optimized.
first phase of composting
- mesophilic phase
both aerobic and some anaerobic activity
second phase of composting
- thermophilic phase
- hottest phase
- water within the pile is release as steam
- fungi replace bacteria
third phase of composting
- temp starts to cool
- fungi are replaced with filamentous bacteria and a few types of mold
- as the pile cools, invertebrates and worms move in
phase four of composting
- dominated by larger soil organisms that mix and shred the remaining material and feed upon the bacteria from the previous phase
- now ready to by transported and applied to the soil
when does composting occur most easily?
- high nitrogen materials are mixed with high carbon materials
- 25-40 parts of carbon for every part nitrogen
brown
high carbon material
green
high nitrogen material
why are smaller particles in compost piles more beneficial?
The smaller particles have a higher surface area that promotes microbial activity and
retention of moisture
what is the ideal oxygen level in a compost pile?
15%
as long as the pores in a compost pile are greater than 10%, the pile can be considered what?
aerobic
- If the oxygen level falls below this 10%, anaerobic
bacteria can really get going and produce sulfur gas, which smells like rotten egg
what is the ideal moisture content of a compost pile to promote bacterial and fungal activity?
40 -60%
what can too much moisture promote? too little?
- mold growth
- anaerobic conditions
improving soil quality
- protects the soil surface
- improves soil properties
- returns nutrients
mineral soil composition
- organic matter
- sand, silt, clay,
- air
- water
organic soils composition
- organic matter
- water
- air
- minerals
composition of SOM
- minerals
- organic matter - living and dead
- pore space
how can SOM effect the soil quality biologically?
- source of energy
- reservoir of nutrients
- soil/plant resilience
how can SOM effect the soil quality physically?
Structure stability
Water retention
Thermal property
how can SOM effect the soil quality chemically?
Cation exchange capacity
Soil pH
Binding ofSOM to soil minerals
what is soil organic matter like?
a sponge and can supply water-holding capacity to plants
what is the main food source for soil microbes?
SOM
- energy stored in SOM carbon to carbon bonds
carbon storage in the atmosphere
750 Pg C
- stored as CO2
carbon storage in vegetation
610 Pg C
- stored as organic c
carbon storage in soil
1580 Pg C
- stored as organic c
recycling options of organic wastes
- repurposed
- burned
- applied to soil
controlled conditions of compost pile
- Carbon to nitrogen ratio
- Distribution of particles sizes in the pile
- Moisture content
- Oxygen content
- Temperature
ideal temperatures for each composting phase
Phase 1: 90-130
Phase 2: 130-140
Phase 3: 60-130
Phase 4: 60
types of composting piles
Static pile
Windrow
Bin
Forced aeration windrow or pile
