80 \ /5500 OUUU
 4080

 6600
 60 \ V 6800

P205
kg/ha
 40

 C

 20 A



 0
 0 50 100 150 200 250 300

 N (kg/ha)


FIG.VI-11. Smoothed product contours and budget lines.

achieved with approximately 37 kg/ha of N and 18 kg/ha of
P, represented by point A on Fig. VI-11. If a farmer has
$400 to spend, maximum yield will approximate 5450 kg/ha
and will be achieved with approximately 80 kg/ha of N and
25 of P, at the intersection labeled point B. With $600
to spend, maximum yield would approximate 5930 kg/ha and
would be achieved by utilization of approximately 123
kg/ha of N and 30 kg/ha of P (point C on the figure).
Similarly, best combinations and yield levels can be
estimated for other budget amounts, such as $1000 and
$1400. The cost of moving from one budget line to the
next and the value of added yield can be calculated to
determine profit or net return for different levels of
fertilizer use (Table VI-6). In this example, taken from
an earlier period when fertilizer prices were low, it pays
to apply fertilizer to produce nearly 7000 kg/ha of rice.
If the price of fertilizer were double that used in the
example, profit would decrease after the $1200 budget
line.