Final Exam Flashcards
What are some examples of organic amendments?
*compost–decomposed plant material
*manure–decomposed waste
*non-legume cover crops
*legume cover crops
What are the advantages of organic amendments?
-increased aggregation
-increased water holding capacity
-increased CEC
-increased water infiltration
-adds nutrients (nitrogen, phosphorous, potassium, etc.)
Percentage of N, P, and K from organic amendments?
percentages vary but are generally below 5%
What are cover crops?
*non cash crop grown to amend soil, may be mown or left standing
*increase soil OM, add nutrients (after decomp. OM), tie up nutrients in living plants to prevent nitrate leaching, reduce erosion, suppress weeds
Attributes of legumes
-produce nitrogen
-add OM
-some provide nectar sources for pollinators
and beneficial insects
Attributes of Grasses
-tie up nitrogen
-add OM
-fibrous roots
Attributes of Brassicas
-long tap root
-may have some biofumigant property when incorporated
Attributes of Sunflowers/Buckwheat
-add decorative elements for agrotourism
-provide habitat and food source for pollinators and beneficial insects
What factors should you consider when choosing a cover crop?
- What type of cover crop? (legume, grass, etc.)
- Annual or Perennial? Does it self-seed?
- When will the cover crop be actively growing?
-cover crops don’t normally get irrigated, must be grown late fall/winter/early spring
-most SJV cover crops are chosen to die/go dormant during warm season
-if not they may need to be killed so they don’t compete with crops for water
-in either case they should be mown, and may be tilled under
Describe the symbiotic relationship between rhizobia and legumes
-are present in legume root nodules
-bacteria are able to harvest nitrogen as N2 from the air and can convert it to ammonium (then converted into nitrate) so it is available to the plant
-in return, bacteria receives carbohydrates from the plant
How can you tell the difference between rhizobia and root nematode nodules?
-root nodules that are slightly pink on the inside indicates the presence of healthy rhizobia bacteria
Why should legume seeds be inoculated?
-not all strains of rhizobia are naturally present in the soil all the time, or may not be present in high amounts
When does N from legumes become available to a crop?
-Nitrogen fixation rates peak just before bloom
-Nitrogen that is fixed is available to the legume when it is actively growing
-Nitrogen will not be available to the crop until the dead legume material begins to decompose
What affects the decomposition rates of cover crops?
-temperature
-soil moisture
-whether the material is incorporated in the soil or left on the surface
What is the efficient legume that fixes N?
the ‘Lana’ wooly pod vetch (cool season annual that reseeds itself)
Are summer active legume cover crops recommended for our area? Why or why not?
-not a standard practice
-growers concerned of costs, whether they will grow without irrigation, and whether it will take water and nutrients from the crop
-compete with crops for water–not recommended for our area
What is the purpose of planting a grass cover crop?
-grasses can take up large quantities of nitrogen from soil, reducing nitrate leaching
-to purposefully reduce nitrogen, wheat, oats or barley are often used and harvested as a crop, removing nitrogen from the soil
-can be planted to release N into the soil very slowly–have a high C:N ratio
What is the purpose of planting a Brassica cover crop?
-Several species in the mustard family can uptake large amount of nitrogen like grasses do, but decompose more rapidly
-Some brassicas (mustards) produce compounds that are toxic to soil-borne organisms when incorporated–potential for some biofumigant effect
*efficiency of fumigant action is variable
Why is understanding the carbon cycle important?
-organisms needs carbon dioxide to survive
-helps us track fuel used by all living organisms
-excess carbon causing global warming
What are the key parts of the carbon cycle?
-photosynthesis by plants
-respiration by plants, animals and microorganisms
-decomposition of plants, animals and microorganisms
-combustion of fuel
What is decomposition?
breakdown of large organic molecules into simpler components
What are the factors controlling rate of decomposition?
- Moisture
- Temperature
- Contact of OM with soil
- Carbon to Nitrogen ratio
Describe how C:N ratio affects decomposition.
*most microorganisms require a certain amount of nitrogen to decompose carbon materials
-Low C:N ratio=they have lots of available nitrogen, will decompose relatively quickly, and plant available nitrogen will be released into the soil
-High C:N Ratio=they will decompose slowly and may tie up all available nitrogen
-microbes scavenge the soil for nitrogen, take all of it up, and none is available to plants to take up
List 3 materials with low C:N ratio
-legume cover crops
-grass clippings
-finished compost
List 3 materials with high C:N ratio
-bark chips
-mulch
-newspaper
What is humus?
-most soil OM decomposes relatively quickly
-Humic substances do not – Humin, Humic acids, Fulvic acids
-Humic substances are highly complex polymers that are extremely resistant to decay
Why is humus important in soil?
-play a part in plant health, increase water uptake, stimulate root imitation and elongation and enhance growth of shoots
-has high CEC
What is char?
-when a fire occurs, not all of the fuel undergoes total combustion
-some undergoes pyrolysis, where OM is heated to 250-500 degrees C under low oxygen conditions
-leaves behind char (charcoal)
Why is char important and what role does it play in arid climate soils?
-in forest ecosystems, 5-10% of soil OM is char
-in grasslands, 40-50% of soil OM is char
-has many of the same properties as humus
-high CEC
What is peat used for?
-use for plant “soil” mixes and other horticultural uses, like turfgrass, and is also burned as fuel source in some places
-it is mined from peat bogs in canada, scotland and russia
Why is the use of peat not recommended?
-Peat is a huge natural carbon sink, and when we dig it u and let it decompose (burn it), all of the carbon is released into the atmosphere
-if we stop using peat now, it is estimated that it will take 2000 years to sequester the carbon lost in the past 50 years
What can peat be replaced with?
-more sustainable alternatives include coco coir and compost
How mobile in zinc in plants?
is not as mobile in plants; signs of deficiency appear in the leaves first
Symptoms of Zinc deficiency?
-decrease in stem length and rosetting of terminal leaves
-reduced fruit bud formation
-mottled young leaves (interveinal chlorosis)
-dieback of twigs after first year
-striping or banding on corn leaves
How mobile is iron in plants?
is not very mobile; deficiency shows in young leaves first
How mobile is manganese in plants?
-not very mobile; deficiency begins in young leaves