where F is the amount of fertilizer nutrient
applied (kg ha -1 ); P F represents the price per
kg of fertilizer; G P represents the price per kg
of paddy; and b 1 and b 2 are constants fitted by
regression.
NOTES:
As a rule of thumb, optimal rates
determined on an economic basis are
smaller than those required to produce
maximum crop yields. Economic yield
targets usually do not exceed 80% of the
maximum potential yield (Y max , Section
2.1). The ‘nutritional balance’ approach
described in Section 2.5 focuses on
achieving the physiological optimum in
terms of crop nutrient uptake. In most
cases, this physiologically optimal yield is
not very different from the optimal
economic yield.
The benefit-cost ratio, BCR =
is often used to assess fertilizer rates or
fertilization technologies. For a nutrient
that follows a diminishing response form