Fertigation
scheduling
is
the
amount
of
fertilizer
to
be
applied
at any point in time so that before the next fertigation the plant
has been able to assimilate a sufficient quantity of the fertilizer.
Fig. 2 shows a typical cumulative N assimilation by plants with
respect to days after planting. For instance, let us assume that dur-
ing the time period between t1 and t2, sugarcane plants in an area
assimilates 20 kg/ha of nitrogen. Let us also assume that during
this
time
period,
one
can
expect
4
kg/ha
of
volatilization
loss
and
1 kg/ha of deep drainage loss. If, in this situation, 25 kg/ha of nitro-
gen is applied at time t1, 20 kg/ha of nitrogen will be available for
the
plant
in
the
root
zone.
This
method
of
applying
fertilizers
is
called a “growth curve nutrition approach”. Butler et al. (2002) have
adopted a growth curve nutrition approach for fertigation schedul-
ing for sugarcane. One disadvantage of this approach is that it does
not
take
into
account
the
carry-over
of
a
nutrient
from
previous
periods. Additionally, for the situation discussed above, the spatial
and temporal distribution of urea, ammonium, and nitrate may be
such
that
less
than
25
kg/ha
of
nitrogen
can
be
taken
up
by
the
roots.
Therefore, a certain quantity of excess nitrogen must be applied in
order to provide sufficient amount of nitrogen to meet assimilation
requirements.