Module 7: Nitrogen and Phosphorous Cycles Flashcards
plant nutrients
nitrogen, phosphorous, magnesium, calcium, and a few other elemtnts
how can we determine plant growth in any land-based ecosystem?
- optimal temperature
- moisture
- light condition
what is distribution of a crop based on?
- optimal temp
- light
- soil conditions
what impacts management practices?
soil properties and climate
- igher
quality soil means fewer inputs are required to grow crops. Hence, lower quality soils require
more water, more nutrients to maintain a viable crop yield
how much nitrogen is in the atmosphere?
78%
what forms of nitrogen can plants assimilate?
- nitrates
- nitrites
- ammonium
legumes
soybeans, clover, peanuts, kudzu
nitrogen fixing bacteria
- convert atmospheric nitrogen into ammonia
- do this through an enzyme called nitrogenase which is the only biological enzyme that can break the nitrogen triple bond
how else can ammonium be made?
- other decomposers like fungi, protists, and other kinds of bacteria
nitrifying bacteria
- can take ammonia from the nitrogen fixing bacteria and turn into nitrates and nitrites
denitrifying bacteria
metabolize nitrogen dioxide and turn back into nitrogen has using a special enzyme called nitrate reductase
what is unique about the phosphorous cycle?
- only element that does not involve the atmosphere
phosphorous cycle
- re-exposed rocks with water eroding them and phosphates are dissolved into water
- immediately available to plants
- decomposers can break down living things and integrate phosphorous back into the soil or water
what are the three categories of fluxes?
additions, losses, and internal transformations
- key to determining nutrient availability in any ecosystems
nutrient additions
through atmospheric deposition, nitrogen fixation, and mineral weathering of rocks in phosphorous minerals
- very low and not enough to support plant annual growth requirements
how are plant nutrient needs met?
decomposition and mineralization
- internal transformation
additions in target ecosystem
- atmospheric deposition through rain or dust
- weathering of rocks or minerals
- biological nitrogen fixation
losses in target ecosystem
- leaching of nutrients with water
- gaseous losses to the atmosphere
- erosion of soil by wind or water
transformations in target ecosystem
- keep nutrients stored
- still active and still available for plant and microbial growth
what is an important distinction between the phosphorous and nitrogen cycle?
almost all the fluxes within the nitrogen cycle are mediated by microbes
- the phosphorous cycle is mediated by mineralization and immobilization
mineralization
the conversion of organic nitrogen and phosphorus to inorganic
nitrogen and phosphorus that are soluble in water and available for plant and microbial uptake
nitrification
only takes place in the presence of oxygen and results in the production of nitrate
how can microbes gain energy?
from converting ammonium to nitrate
mobilization
- reverse of mineralization
denitrification
only takes place in the absence of oxygen and
is how we get nitrogen back from the soil and the atmosphere
how long does it take to form 38 cm of rock?
20,000 years
how is nitrogen primarily lost?
nitrate leaching and denitrification
how is phosphorous primarily lost?
erosion
what are some similarities between the nitrogen and phosphorous cycles?
- stored in soil, water, and living biomass
- movement through mobilization and mineralization
why does phosphorous readily fixed in the soil?
by adsorption and precipitation processes
what is phosphorous sorption and precipitation high dependent on?
pH
- very soluble at neutral pH
acidic soils
high in aluminum or iron
- phosphate readily sticks or absorbs to the surface or locked to the actual soil particles
basic soils
- more calcium
- calcium and phosphate in the soil solution immediate form calcium phosphate forming a precipitate
what is the pH of most agricultural soils?
a little above or a little below neutral
nitrogen mineralization
the conversion of organic nitrogen into
ammonium, an inorganic form of nitrogen that is soluble in water. Since ammonium is soluble in
water, we consider it to be part of the soil solution
what are the 5 factors that impact plant growth?
Climate
Soil properties
Management
Plant age
Plant genetics
Irrigation schedule
Nitrogen nutrient management
nutrient cycles: pools
- plant (living) biomass
- soil
- minerals
- water bodies
- atmosphere
comparisons of natural and conventional agricultural ecosystem
- natural ecosystems: additions are small, losses are small, Internal transformations provide a plant’s daily nutrient needs
- agricultural ecosystem: additions are greater, losses are greater, Internal transformations cannot meet a crop’s daily nutrient needs without the additions of fertilizers
what is the key to understanding nutrient cycles is to identify what factors?
- pools
- fluxes
- ecosystem boundaries
differences in inputs of N and P
- P - born of rock (weathering, dust)
- N - born of air
differences in transformations of N and P
- N - microbially mediated
- N - involves transfer of energy
- P - involves P minerals
differences in losses of N and P
- N - losses by leaching and gas production
- P - losses by erosion
similarities between N and P
- immobilization and mineralization
- connected the carbon cycle via decomposition and soil organic matter formation
best management practices promote
- Right amount of fertilizer to minimize overloading
- Conditions that promote organic matter, which promote immobilization of N and P
- Conditions that minimize erosion and leaching losses
