382 INVESTIGATION BY CULTURE EXPERIMENTS 



phosphate (compare O2 and 04 for the 3o-year and 25-year 

 periods). 



Where nitrogen has been applied without phosphorus, the stimu- 

 lating effects of the alkali salts is still apparent, probably because 

 they continue to liberate some phosphorus from the soil. Where 

 both nitrogen and phosphorus are provided, the effect of the al- 

 kali salts is most marked, and here it is increasing, very possibly 

 because all of the potassium needed by the larger crops is not liber- 

 ated from the soil on account of lack of decaying organic matter. 

 Here it will be seen, however, that the sodium in sodium nitrate 

 without potassium (plot N2) produces even better results than the 

 alkali salts, including potassium (plots A4 and N4), but this com- 

 parison is complicated by the fact that ammonia nitrogen and 

 nitrate nitrogen may have different effects, and the chlorin and 

 sulfate radicle may also produce some effect. 



It is of special interest to compare the marked residual effect of 

 farm manure on plot 7-1, Hoos field, with the absence of such an 

 effect from the heavy applications of commercial fertilizers (in- 

 cluding 172 pounds of nitrogen) on plot 16 of Broadbalk field. (See 

 Table 62.) However, it should be kept in mind that plot 7-1 re- 

 ceived 314 tons of manure during the 20 years (1852 to 1871), 

 which is equivalent to almost 6 tons per acre a year for the entire 



55 y ears - 



At 40 cents a bushel for barley, the manure applied to plot 7-2 

 has been worth about 85 cents a ton, while that applied to plot 7-1 

 has already paid $1.36 a ton for itself, not deducting interest on 

 investment or counting the remaining residual effect, plot Ci being 

 used as the basis for comparison. 



A comparison of plots N2 and 7-2 shows the marked superiority 

 of the farm manure in a dry season (1893), while the commercial 

 fertilizers give nearly as good results in normal or wet seasons, and 

 probably would surpass the farm manure if the nitrogen were in- 

 creased sufficiently. 



If the 43 pounds of nitrogen cost $6.45 and the 29 pounds of 

 phosphorus $3.48, and if barley is worth 40 cents a bushel, the 

 ammonia nitrogen has left a deficit of $1.97 a year for the 55 years, 

 while phosphorus, in addition to nitrogen, has overcome $1.92 of 

 the deficit, leaving a net loss of 5 cents per acre per annum. 



