116 
The nitrogen in the fertilizer cost per acve.<- 25. 2422)42 2 see cele $1 80 
Rhesphosphoricyacid= costsper ACrel oc ser as cco ie oho ere 1 50 
(BhHESPOtASM COST PEL FACTO 4 sciaiee wave icusts, exe clste eee ead eke ee 1 10 
The complete fertilizer cost per acr@a5—-284.-..........-.-92 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 8.8 bushels at a cost of $1.10. As wheat sold at 90 cents 
per busiel 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 know that 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 18 bushels per acre and that of the unfertilized plots being only 
2 bushels. 
In these experiments the nitregen 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 cyverlooked in planning such experiments, 
and for a considerable time the indirect etfects may be so great as to mis- 
lead one who does not take them into consideration. Thus the gypsum 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 
im 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 indirect 
effects mask the direct effects. 
