Rice
kg/ha


7500



7000



6500




6000-



5500




5000-

 .">
 :t


0 Observation
X Average


 I I
0 75 150


225


300


 N kg/ha

FIG.VI-3. Response of IR-22 rice to nitrogen in Corinto,
 Cauca, with P205 = K20 = 40 kg/ha.

 The method is based on the fact that the first
derivative of a quadratic function is a straight line
(Fig. VI-4). The first derivative is a value equal to the
slope of the function for any value of X, or in this case
the input nitrogen. Associated with an increase in
nitrogen from 0 to 150 kg/ha (AN1) is an average increase
of 1325 kg in the yield of rice (AY1). Here, the symbolA
means "change in." Hence, AN1 can be read, "the change