USE OF PHOSPHORUS IN DIFFERENT FORMS 



257 



TABLE 41. BALANCE SHEET FOR NITROGEN AND PHOSPHORUS IN MANURE- 

 PHOSPHATE EXPERIMENTS 

 Totals for Three Years, Pounds per Acre: in Part roughly Estimated 



nitrogen fixation. In other words, that the draft upon the soil 

 by the crops grown is likely to be greater rather than less than 20 

 pounds above that supplied by the manure and clover, and, in 

 addition to this, there are losses of nitrogen in drainage waters 

 probably exceeding all other additions (as in rainwater, by azo- 

 tobacter, etc.). The loss of nitrogen by drainage is no doubt 

 much greater from the best-treated plots than from the untreated 

 plots. Failing nitrogen may finally reduce the phosphorus effect. 

 On the whole, it seems clear that nitrogen must limit the crop 

 yields on these four plots treated with manure and phosphate. 

 On the other hand, in every case the phosphorus applied exceeds 

 the amount removed in the crops, so that, instead of there being 

 any draft upon the soil, there is a positive increase in the phosphorus 

 content of the soil above the crop requirements. This increase 

 varies from 2 and 13 pounds with acid phosphate to 22 and 33 

 pounds with raw phosphate. If nitrogen is the limiting element on 

 all of these manure-phosphate plots, it is plain to see why the raw 

 phosphate gives practically no larger yields than the acid phos- 



