Nitrogen cycle Flashcards
what percentage of the atmosphere is nitrogen
78%
nitrogen cycle definition
the process by which N is gained or lost in the soil, absorbed by plants and returned to the soil as organic matter
2 forms of available N in plants
nitrate (No3)- and ammonium (NH4)+ (ammonium is rapidly converted to nitrate via nitrification
define nitrification
the process by which ammonium N is converted to nitrate N for crop uptake
what soil temperature does nitrification take place
above 4 degrees Celsius
define denitrification
the process in which nitrate N is reduced to nitrous oxide (N2O) and nitrogen gas (N2). This typically occurs in warm anaerobic soils often due to compaction and water logging
define volatilisation
the process by which ammonia gas (NH3) is lost from the soil when the concentration of ammonium N exceeds the absorptive capacity of the soil
conditions of volatilisation
light, warm, drying alkaline soils are prone to volatilisation. Most ammonia emissions come from livestock manures during storage and spreading and some come from the application of urea
how can nitrous oxide emissions be minimised
match N inputs with crop requirements
soil nitrogen supply (SNS) definition
the amount of nitrogen (kg/ha) in the soil that becomes available for uptake by the crop from establishment to the end of the growing season taking into account nitrogen losses
SNS equation
SNS= SMN + estimate of total crop N + estimate of mineralizable N
what is leeching
the loss of nitrate N (NO3-) via water
what is fixation
the process where atmospheric nitrogen gas (N2) is converted to organic N (R-NH2). This is primarily done by bacteria in legume nodules or industrial fertiliser production.
what is mineralisation
the process in which microbes convert organic N to ammonium N. This occurs in warm, moist well aerated soils.
immobilisation
the process in which soil organisms consume nitrate N or ammonia N and convert it to organic N locking it up within their cells until they die and decompose
