All components of N balance therefore are known, assumed or
neglected, with the exception of N losses to deep percolation and
surface drainage as water-soluble nitrates. N inputs from fertiliser
have been calculated from the fertilisers’ formulae and application
doses. N inputs from rainfall and irrigation water were calculated
from data on N contents, average precipitation and irrigation data
over the period under consideration (cropping cycle). Using data
from the Pollution Control Department of Thailand (PCD) and from
the Royal Irrigation Department of Thailand (RID), we calculated
and used an average NO-
3 concentration of 0.7 mg.l1 in precipitation,
and 0.11 mg.l1 in irrigation water. Rainfall data from the
Thailand Meteorological Department rainfall stations located in the
study area were used (as shown in Table 3).