51 



first half of this increased application (from 60 to 76 pounds) increases pro- 

 duction much more than the last half (76 to 92 pounds) (fig. 7). The first 

 half increases production by 0. 18 ton per acre and the second half by 0. 07 

 ton. This means that the second half of the nitrogen application does not 

 produce its proportionate share of the needed increase, 0. 125 ton per acre, 

 and that consequently it costs more than it returns. The first half produces 

 more than its proportionate share and returns more than it costs. This ex- 

 plains the statement that, under these conditions, the most profitable rate 

 is midway between 60 and 92 pounds for curve "B. " Theoretically, it might 

 differ slightly from this because of irregularities in the nitrogen response 

 curve, but for practical application it is near enough to the correct theoretical 

 application to be used. 



TONS PER ACRE 



100 



LB. OF AVAILABLE NITROGEN APPLIED 



U. S. DEPARTMENT OF AGRICULTURE 



Figure 7. Select section of curve "B" fronn figure 6 



NEC. 59(3)-2665 AGRICULTURAL RESEARCH SERVICE 

 tl-i-iM 



