Global terrestrial N cycling: estimates of pools and transfers (transfers in 106 tonnes atmos phere(mainly n2) 39 X105tonnes N2 fixation nitrate denitrification biological 139 ~150 non-biological 50 plants, animals, microorganisms 1.3 x 1010 tonnes, soil, peat and litter 30x 1010 tonnes Nitrate leaching 18-33 rivers and then oceans
Global terrestrial N cycling: estimates of pools and transfers (transfers in 106 tonnes) atmosphere (mainly N2 ) 39 x1015 tonnes N2 fixation biological 139 non-biological 50 ‘nitrate’ 32 rivers and then oceans denitrification ~150 Nitrate leaching 18-33 plants, animals, microorganisms 1.3 x 1010 tonnes, soil, peat and litter 30 x 1010 tonnes
Main forms of organic N in soil ● amino acias used quickly by soil microorganism proteins variable availability to soil micro-organisms complex polymers Chitine(几丁质), lignin(木质素) not very available
Main forms of organic N in soil • amino acids – used quickly by soil microorganism • proteins – variable availability to soil micro-organisms • complex polymers – Chitin(几丁质), lignin(木质素) – not very available
N is dominated by biological processes crop atmosphere soil N2 fixation stable labile InorganIc plants organIc microbe labile soil stable InorganIc solution organIc leaching(NO3) erosion
N is dominated by biological processes erosion soil solution stable inorganic labile inorganic microbes plants stable organic labile organic leaching (NO3 - ) crop atmosphere N2 fixation soil
n availabilit NO3 and NH are available to plants Low buffering capacity in soil Biological cycling of n between organic matter and inorganic forms in soil solution Mineralisation(矿化作用) depends on soil moisture and temperature and C: N ratio of organic inputs Biological fixation of gaseous N2 (fertilizer applications
N availability • NO3 - and NH4 + are available to plants • Low buffering capacity in soil • Biological cycling of N between organic matter and inorganic forms in soil solution • Mineralisation(矿化作用) depends on soil moisture and temperature and C:N ratio of organic inputs • Biological fixation of gaseous N2 • (fertilizer applications)
Decomposition of organic N produces NH4 atmosphere nitrogen fixation organIc NH NO3H+NO2/NO/N2 N soil solution Ammonifying Nitrifying Denitrifying organisms organisms organisms
Decomposition of organic N produces NH4 organic N NH4 Ammonifying organisms NO3 Nitrifying organisms NO2 /NO/N2 Dentrifying organisms atmosphere nitrogen fixation soil solution