A THIRTY-YEAR FERTILIZER TEST. 135 



For the first five crops the two treatments gave practically the same 

 results. For the last five crops, jdelds were maintamed fairly well by the 

 manure treatment, and not at all well on the fertiUzer treatment. This 

 difference in plot behavior may be explained, in part, either by the fact 

 that manure contained organic matter while the fertiUzer used did not, 

 or by the difference in plant food. The amounts of plant food applied 

 per acre in the two contrasted treatments are as follows: — 



Pounds per Acre (Aver- 

 age PER Year). 



Applied in 

 Manure. 



Applied in 

 Fertilizer. 



Nitrogen 

 Phosphoric acid 

 Potash 

 I 



108 

 118 



169 



The amount of manure used is larger than could have been produced 

 had all crops gro\\'n been fed to animals and all of the manure produced 

 carefuU}^ saved and returned to the land. For this reason the fact brought 

 out in the foregoing table has no great significance in its bearing on actual 

 practice. 



Response of Corn to Fertilizer Nitrogen. — There was wide variation in 

 the degree of response of the crop to the use of fertilizer nitrogen. In two 

 cases there was apparently a significant decrease in crop produced by 

 such use, — a result which, while unusual, is by no means impossible. 

 Owing to its favorable effect on nitrification, corn seldom shows marked 

 response to the use of this plant food except under those conditions where 

 the soil supply of organic nitrogen is very limited. Less response would 

 therefore be expected on the com crops following legumes or grown on 

 sod than on the com crops following non-legumes or grown on stubble, 

 while the greatest increase would be expected from those com crops which 

 are three years from a legume. 



The following tabulation was made to see if this expectancy be sup- 

 ported by facts. Owing to the comparatively small variation in checks, 

 the yields on the phosphoric acid and potash plot are compared directly 

 with those on the complete fertilizer i)lots. The yields on the manure 

 plots are included, as significant of results secured where there was a 

 sufficiency of plant food and organic matter in the soil. Since moisture 

 and temperature conditions influence nitrification, the departure from 

 normal of both precipitation and mean hourly temperature is tabulated 

 alongside the yield records. 



