Terrestrial Nitrogen Cycle

Question 1

____ is the conversion of atmopheric nitrogen to a plant available form. This occurs either through an industrial process, as in the production of commercial legumes (alfalfa, clover).
N2 -> NH3 -> R-NH2
nitrogen gas -> ammonia -> organic nitrogen

Answer 1

Nitrogen fixation
N2 fixation

Question 2

___ is a nitrogen loss pathway that is of concern to water quality. Soil particles are negatively charged and do not retain nitrate well. Rates increase as greater rainfall and nitrogen inputs (especially outside the growing season).

Answer 2

Leaching

Question 3

____ is the loss of nitrogen through the conversion of ammonium to ammonia, which is released to the atmosphere. Losses increase at higher soil pH and conditions that favor evaporation (eg. hot and windy)
Urea -> ammonium -> ammonia

Answer 3

Volatilization

Question 4

___ is the process by which microbes decompose organic nitrogen from organic matter to ammonium. It occurs rapidly in warm, well-aerated and moist soils.
R-NH2 -> NH3 ->NH4+
organic N -> ammonia -> ammonium

Answer 4

mineralization

Question 5

___ occurs when nitrogen is lost through the conversion of nitrate to gaseous forms of N. This happens when the soil is saturated with water (aeration is poor).
NO3- -> NO2- -> NO ->N2O -> N2
nitrate -> nitrite -> nitric oxide -> nitrous oxide -> dinitrogen gas

Answer 5

denitrification (*leaky pipeline)

Question 6

____ is the process in which nitrate and ammonium are taken up by soil organisms and become temporarily unavailable to plants. It is greater if materials with a high C:N ratio are added to a soil.
NH4+ and/or NO3- -> R-NH2
ammonium and or nitrate -> organic nitrogen

Answer 6

immobilization

Question 7

____ is the process by which microbes convert ammonium to nitrate. It produces the most plant available form of nitrogen. The process is most rapid when soils are warm (>5 degrees celcius), moist and aerated.
NH4+ -> NO2- -> NO3-
ammonium -> nitrite -> nitrate

Answer 7

Nitrification