N uptake from rice plants was calculated from the average N
contents of the average mass of exported crop parts (grain and
ears). N losses due to emissions to the air in the form of N2O, NO
and NH3 were calculated as shown in previous sections. N2 is
emitted during the last phases of denitrification. Although not a
pollutant, N2 needs to be assessed to complete the whole mass
balance. Brentrup et al. (2000) proposed an emission factor of 9% of
all N fertilisation. Although their emission factor corresponded to
annual crop conditions under temperate climate, it was used in this
study, in the absence of more adapted data.