Midterm Flashcards
How do you calculate relative humidity?
((Current Vapor Pressure)/(Saturation Vapor Pressure))x100
Does the amount of water that air can hold increase or decrease with temperature?
The amount of water air can hold increases with temperature.
What is the dew point?
Dew point is the temperature when water will condense for a given vapor pressure.
How does water leave the soil?
Evaporation, transpiration, drainage (gravitation force)
How does water get into soil?
Percolation
What is water potential?
Quantitative description of the free energy states of water (ability to do work)
What is the water potential equation and components?
YW = ΨP + ΨS + ΨG ΨP = pressure potential, measure of turgor in plant cells, always positive unless plant is wilted ΨS = solute or osmotic potential due to dissolved solutes in cells, always negative unless pure water ΨG= gravitational, only important in tall trees
What is SPAC and how does it work?
Soil plant air continuum. Water moves down its potential gradient from high to low -> water taken up roots and up stem into leaves and out in to the atmosphere.
How can you prevent nitrate leaching?
Careful irrigation and fertilizer management. and cover cropping
How much irrigated land is salt affected and how much is added each year?
About 20% globally is salt affected with 2,500-5,000 km2 lost production added each year.
How do you manage salinity in irrigated ag.? (Plant placement?)
Double row beds, salt accumulates in middle. Wide/sloping beds, plants on low side salt accumulates on high side. Alternate furrow irrigation and the salt will accumulate in non watered furrow.
Does water move up or down its potential gradient?
Water moves down potential gradient from high potential to low potential.
What is an adaptation to too much water available?
Hollow roots so the air can diffuse down.
What is the rain shadow effect?
As the air rises and condenses on one side of the mountain then the air without much moisture continues on to the other side where it is now dry air without much or any moisture.
Define soil fertility.
The capacity of a soil to provide nutrients required by plants for growth, and is one component of soil quality.
Define soil quality.
Broad concept, soil capacity to:
- Accept, hold, release and mineralize nutrients and other chemical constituents.
- Accept, hold, and release water to plants, streams and groundwater
- Promote good root growth and maintain good biotic habitat for soil organisms
- Resist degradation
Name two goals of a sustainable fertility/soil management program.
(1) To sustain good productivity and crop quality (min. disease/pest susceptibility, balanced nutrient supply for crop, time season nutrient availability to correspond with crop demand)
(2) Sustain environmental quality (minimize soil quality, min. off-farm impacts)
List the soil profile horizons (5) and the layers (2)
O Horizon, A Horizon, (Eluviation Layer) B Horizon (Illuviation Layer), C Horizon, R Horizon.
What is O horizon composed of?
composed of plant litter at various levels of decomposition and humus
What is A horizon composed of?
primarily mineral particles mixed with humus and organic matter
zone of translocation with eluviation moving finer particles and soluble substances
dark in color, usually light in texture and porous
often differentiated into a darker upper horizon and lighter lower horizon
What is B horizon composed of?
mineral soil layer strongly influenced by illuviation
receives material eluviated from the A horizon
has a higher bulk density than the A horizon due to enrichment of clay particles
may be colored by oxides of iron and aluminum or by calcium carbonate illuviated from above
What is C horizon composed of?
is composed of weathered parent material
texture quite variable with particles ranging in size from clay to boulders
not been influenced by pedogenic processes, translocation, and/or organic modification
What is R horizon composed of?
consists of unweathered bedrock.
What is the typical size particles for Sand, Silt and Clay?
Sand: 0.05mm - 2mm
Silt: 0.002mm - 0.05mm
Clay: <0.002mm
Define: Texture (soil)
Particle size distribution
Define: Structure (soil)
Aggregate properties, size and stability.
Define: Tilth (soil)
Porosity and workability.
What is the optimal pH range for soil for most nutrients? And how can a grower increase pH if it falls too low?
6 - 7; add lime
Name a crop that can survive acidic conditions and moderately acidic.
Blueberries 4.5-5.0pH (acidic)
Peanuts, watermelon, & sweet potato 5.0-6.0 (moderately acidic)
What is CEC and its relevance to soil minerals?
Cation Exchange Capacity (amount of cations that can be held).
Many mineral particles are negative charged which repel negatively charge ions and attract positively charge ions, or cations.
How is CEC in soil determined?
By the types of clay minerals present and amount of organic matter, both of which have a negative charge.
Define: Buffer capacity (soil)
The higher a CEC the more cations that can be supplied by the soil and replenished.
At a low soil pH what ions is the CEC mainly occupied by?
H+ and Al3+ (acidic cations)
At a high soil pH what ions is the CEC mainly occupied by?
Ca2+, Mg2+, K+, and Na+ (basic cations)
What is SOM made up of?
33-50%: Decomposing organic matter
33-50%: Stabilized organic matter (humus)
10%: Fresh reside
<5%: Living organisms
What are some effects of SOM?
- Improved soil structure and porosity by helping build and stabilize aggregates
- Improve water holding capacity
- Improve CEC
- Provide a reservoir for nutrients that are released as OM is decomposed
- Provides food for soil microbes to decompose (basis of soil food web)
Describe a quick soil food web.
OM
2nd level: Bacteria/Fungi/Nematodes(root feeders)
3rd level: Arthropods (Shredders&Pred.) / Nematodes (Predators)
4th level: High level predators birds animals
What is the chemical equation for photosynthesis?
6CO2 + 6H20 +Light Energy = C6H1206 + 6O2
What happens during photoinhibition?
The plant is producing so much oxygen that it reacts with rubisco and inhibits the plant from fixing carbon to make sugar - too much light
What would be the process for C3 plants?
Phase 1: Carbon fixation with rubisco 3 CO@.
Phase 2: Reduction into G3P a sugar, which is used as output for the plant and then 5 are used to regenerate CO2 acceptor
What is the enzyme that fixes CO2?
Rubisco
What is the process for C4 plants?
C4 plants have PEP carboxylase which is not sensitive to CO2:02 ratio to store the CO2. Then it is transferred to bundle sheath cells where it is processed at a controlled CO2:02 ratio.
What is the process for CAM?
During the day the plant will close stomata and fix CO2 into simple sugars. At night the stomata is open for active flow of H2O and CO2.
What ‘rules’ in the phosphorous cycle?
Soil chemistry and mineralogy. Fertilizer, plant residue, weathering of rocks, manures & OM are inputs for this. In low P soils mycorrhizal fungi are important.
What bacteria forms a symbiotic relationship in the nodules of legumes to fix N2?
Rhizobium
What are the key microbial processes for nitrogen & N transformations?
Mineralization: Organic N -> inorganic N as ammonium (NH4+)
Immobilization: Inorganic N, Ammonium NH4+, Nitrate NO3- :-> Organic N
Nitrification: Ammonium -> nitrite -> nitrate (NO3-)
Dentrification: nitrate -> gaseous forms
What is the Nitrogen Cycle? (Input, components and loss)
Input: Plant residue, manure, atmosphere, N fixation by legumes
Components are: Organic N, Ammonium NH4+, Nitrate NO3-,
Loss: volatization, crop removal, runoff, denitrification, and leaching
What are the goals of a sustainable fertility/soil management program?
To sustain good productivity and crop quality (balanced nutrients, seasonal nutrient availability to meet crop demand, min. disease/pest susceptibility, build soil OM). To sustain environmental quality. (Maintain or improve soil quality, minimize off farm impacts, close nutrient cycles as much as possible)
Why is it good to have a microbial community?
Decomposition of plant and animal material, mobilize and immobilize nutrients, create soils structure by providing “glue” to hold aggregates together and create pore space for air and water movement.
What are requirements of nice soil?
Good structure to provide aeration for oxygen, good water infiltration, moderate pH 6-7.5, low salinity, low levels of potentially toxic elements, balanced fertility
What are some examples of a C3 plant?
rice, temperate grains, legumes
What are some examples of a C4 plant?
corn, sorghum, sugarcane
What are some examples of a CAM plant?
Pineapple, aloe vera, Agave
Where do C4 plants dominate and what kind are they?
Grasslands and they are mainly grasses.
What is significant about light saturation point?
LSP is when the maximum rate of photosynthesis at light saturation has been met, after this photoinhibition will follow where a plant will start to photorespire too much.
What are plant macro-nutrients?
C, H, O - Basic constituents of OM N - Proteins, chlorophyll, enzymes Ca - Cell walls P - Energy transfer Mg - Chlorophyll S - proteins Cl - light reaction K - Ionic balance
Why should one use cover crops?
Fertility management, weed suppression.
What is the difference between Cover/Catch crop and green manure?
Cover crop prevents soil erosion, catch crop catches nutrients left after harvest. Green manure is turned under for soil improvement.
How would you build SOM with a cover crop?
Choose a crop with high biomass. Fall non-legumes: rye, legume/cereal
Provide N and SOM: sub-clover or woollypod vetch.
Summer: Sudan, buckwheat, cowpea, pigeon pea
To use cover crop to provide N what should you do?
Choose a legume that is well suited for the area. Sufficient rhizobia bacteria present in soil to give good root nodule formation. May need to inoculate the soil with rhizobium if first time
What is the typical N contents for cover crop types, annual legumes, perennial legumes and grasses
Annual legumes: 3.5-4%
Perennial legumes: 2.5-3%
Grasses: 2-3%
How do you roughly estimate N from a cover crop?
Calculate above ground dry weight, then multiply by the %N content of biomass to give total N in cover crop.
