116 



The nitrogen in the fertilizer cost per acre $1 80 



The phosphoric acid cost per acre 1 50 



The potash cost per acre 1 10 



The complete fertilizer cost per acre $4 40 



The nitrogen increased the crop 4.7 bushels at a cost of $1.80, the 

 phosphoric acid increased it 26.2 bushels at a cost of $1.50, while the pot- 

 ash increased it S.S bushels at a cost of $1.10. As wheat sold at 90 cents 

 per bushel it will be seen at a glance that all the plant foods were used at 

 a profit, although, of course, we are not in a position to show that the 

 combination is the one most profitable. Nor do we know that this was 

 the most profitable amount. We do kuow tbat it was very profitable even 

 neglecting the value of the increase in the straw and the very striking 

 effect on the clover which followed the wheat. 



The experiment is a typical one for soils in the winter wheat belt, 

 and numerous others could be given showing results of just the same char- 

 acter and even more striking in profits. 



The figures show how the lack of phosphoric acid limited the crop, 

 and they serve to explain why bone gave such increases on these soils that 

 for nearly a generation it was considered the only profitable thing to use. 



In another series at a different place the amounts of the plant foods 

 were varied, but the season was so unfavorable that the crop was limited 

 by other considerations than plant food, the maximum crop being only 

 about 13 bushels per acre and that of the unfertilized plots being only 

 2 bushels. 



In these experiments the nitrogen is supplied from blood, the phos- 

 phoric acid from precipitated calcium phosphate free from gypsum, and 

 the potash from muriate of potash, the purpose being to use materials 

 exerting as little indirect effect as possible. 



This matter is too often overlooked in planning such experiments, 

 and for a considerable time the indirect effects inay be so great as to mis- 

 lead one who does not take them into consideration. Thus the gypsuni in 

 ordinary acid phosphate, amounting to about one-third of its weight and 

 the sodium in the nitrate, may each release so much potash from zeolites 

 in the soil that the plot with nitrate acid phosphate and potash may show 

 little if any increase over that with nitrate and acid phosphate. Compara- 

 tively few experiments exist which have been conducted long enough and 

 in such a way as to shed much light on the extent to which the indire -t 

 effects mask the direct effects, 



