Module 7: Nitrogen and Phosphorous Cycles

Question 1

plant nutrients

Answer 1

nitrogen, phosphorous, magnesium, calcium, and a few other elemtnts

Question 2

how can we determine plant growth in any land-based ecosystem?

Answer 2

• optimal temperature
• moisture
• light condition

Question 3

what is distribution of a crop based on?

Answer 3

• optimal temp
• light
• soil conditions

Question 4

what impacts management practices?

Answer 4

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

Question 5

how much nitrogen is in the atmosphere?

Answer 5

78%

Question 6

what forms of nitrogen can plants assimilate?

Answer 6

• nitrates
• nitrites
• ammonium

Question 7

legumes

Answer 7

soybeans, clover, peanuts, kudzu

Question 8

nitrogen fixing bacteria

Answer 8

• 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

Question 9

how else can ammonium be made?

Answer 9

• other decomposers like fungi, protists, and other kinds of bacteria

Question 10

nitrifying bacteria

Answer 10

• can take ammonia from the nitrogen fixing bacteria and turn into nitrates and nitrites

Question 11

denitrifying bacteria

Answer 11

metabolize nitrogen dioxide and turn back into nitrogen has using a special enzyme called nitrate reductase

Question 12

what is unique about the phosphorous cycle?

Answer 12

• only element that does not involve the atmosphere

Question 13

phosphorous cycle

Answer 13

• 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

Question 14

what are the three categories of fluxes?

Answer 14

additions, losses, and internal transformations
- key to determining nutrient availability in any ecosystems

Question 15

nutrient additions

Answer 15

through atmospheric deposition, nitrogen fixation, and mineral weathering of rocks in phosphorous minerals
- very low and not enough to support plant annual growth requirements

Question 16

how are plant nutrient needs met?

Answer 16

decomposition and mineralization
- internal transformation

Question 17

additions in target ecosystem

Answer 17

• atmospheric deposition through rain or dust
• weathering of rocks or minerals
• biological nitrogen fixation

Question 18

losses in target ecosystem

Answer 18

• leaching of nutrients with water
• gaseous losses to the atmosphere
• erosion of soil by wind or water

Question 19

transformations in target ecosystem

Answer 19

• keep nutrients stored
• still active and still available for plant and microbial growth

Question 20

what is an important distinction between the phosphorous and nitrogen cycle?

Answer 20

almost all the fluxes within the nitrogen cycle are mediated by microbes
- the phosphorous cycle is mediated by mineralization and immobilization

Question 21

mineralization

Answer 21

the conversion of organic nitrogen and phosphorus to inorganic
nitrogen and phosphorus that are soluble in water and available for plant and microbial uptake

Question 22

nitrification

Answer 22

only takes place in the presence of oxygen and results in the production of nitrate

Question 23

how can microbes gain energy?

Answer 23

from converting ammonium to nitrate

Question 24

mobilization

Answer 24

• reverse of mineralization

Question 25

denitrification

Answer 25

only takes place in the absence of oxygen and is how we get nitrogen back from the soil and the atmosphere

Question 26

how long does it take to form 38 cm of rock?

Answer 26

20,000 years

Question 27

how is nitrogen primarily lost?

Answer 27

nitrate leaching and denitrification

Question 28

how is phosphorous primarily lost?

Answer 28

erosion

Question 29

what are some similarities between the nitrogen and phosphorous cycles?

Answer 29

- stored in soil, water, and living biomass - movement through mobilization and mineralization

Question 30

why does phosphorous readily fixed in the soil?

Answer 30

by adsorption and precipitation processes

Question 31

what is phosphorous sorption and precipitation high dependent on?

Answer 31

pH - very soluble at neutral pH

Question 32

acidic soils

Answer 32

high in aluminum or iron - phosphate readily sticks or absorbs to the surface or locked to the actual soil particles

Question 33

basic soils

Answer 33

- more calcium - calcium and phosphate in the soil solution immediate form calcium phosphate forming a precipitate

Question 34

what is the pH of most agricultural soils?

Answer 34

a little above or a little below neutral

Question 35

nitrogen mineralization

Answer 35

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

Question 36

what are the 5 factors that impact plant growth?

Answer 36

Climate Soil properties Management Plant age Plant genetics Irrigation schedule Nitrogen nutrient management

Question 37

nutrient cycles: pools

Answer 37

- plant (living) biomass - soil - minerals - water bodies - atmosphere

Question 38

comparisons of natural and conventional agricultural ecosystem

Answer 38

- 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

Question 39

what is the key to understanding nutrient cycles is to identify what factors?

Answer 39

- pools - fluxes - ecosystem boundaries

Question 40

differences in inputs of N and P

Answer 40

- P - born of rock (weathering, dust) - N - born of air

Question 41

differences in transformations of N and P

Answer 41

- N - microbially mediated - N - involves transfer of energy - P - involves P minerals

Question 42

differences in losses of N and P

Answer 42

- N - losses by leaching and gas production - P - losses by erosion

Question 43

similarities between N and P

Answer 43

- immobilization and mineralization - connected the carbon cycle via decomposition and soil organic matter formation

Question 44

best management practices promote

Answer 44

- 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