USE OF PHOSPHORUS IN DIFFERENT FORMS 255 



the 40 pounds of phosphorus applied in raw phosphate has not pro- 

 duced markedly greater benefit than the 20 pounds in acid phos- 

 phate, these applications having been repeated in connection with 

 manure every three years for twelve years. This is an important 

 and interesting question. It may be best considered in connection 

 with the general average yields recorded in Table 40, which, it may 

 be observed, includes results from the use of kainit, gypsum, and 

 " complete " fertilizers. The amounts of kainit and gypsum used 

 are the same as raw phosphate and acid phosphate; namely, 320 

 pounds with 8 tons of manure per acre every three years. The kainit 

 costs about $15 per ton and the gypsum about $6 per ton. The 

 footnotes to Table 40 give further data, so that any one may make 

 his own computations concerning the increase in yield or profit 

 from every kind of treatment. 



Attention is called to the fact that plot n is a continuation of 

 plot i, and on Series C it is so abnormal that its influence is seen 

 in the general average of every crop. 



By computations from Tables 23 and 40 it is a simple matter 

 to construct most of Table 41, in which a balance is shown for the 

 elements nitrogen and phosphorus supplied and removed in these 

 experiments with manure and phosphates. 



The figures given in Table 40 may be considered as approxi- 

 mately correct, but the amounts of nitrogen furnished by the soil 

 and by the clover residues are roughly estimated. This estimate 

 is based upon the assumption that the total clover tops, aside from 

 the clover hay harvested, will be equivalent to one half of the regu- 

 lar hay crop. These residues consist of (i) the first season's growth, 

 chiefly after the wheat harvest; (2) the fall growth the second 

 season ; and (3) the following spring growth before plowing for 

 corn. These estimates are added to Table 40, not as well-established 

 facts, but rather as suggesting methods of study that deserve 

 further investigation. To one familiar with field conditions it 

 seems certain that the clover is given at least all credit due for 



from plot Ci in computing the increase produced by the raw phosphate by the 

 Ohio method of comparison. As a suitable topic for a debating society, the author 

 suggests the question: 



Shall we use acid phosphate or raw rock phosphate in systems of permanent 

 agriculture? 



