16 



BULLETIN 699, U. S. DEPARTMENT OF AGEICULTUEE. 



Table VII. — Phosphoric acid (PiO^) voided in dung of animals fed tcith phos- 

 phated and unphosphated ensilage. 





Phosphoric acid found. 



Material. 



Total. 



Soluble in 

 0.1 per cent 

 citric acid. 





Per cent. 

 1.17 



5.95 

 6.95 



1.78 



9.34 

 9.34 



Per cent. 

 0.75 



Dung from cow No. 10 (untreated ensilage) plus a quantity of floats equal to that 



.88 





1.05 



Dung from fawTQ heifer (untreated ensilage) 



1.38 



Dung from fawn heifer (untreated ensilage) plus a quantity of floats equal to that 



1.47 





1.86 







Apparently the combined processes of fermentation and subse- 

 quent digestion of the phosphated ensilage produced small increases 

 in the citric solubility of the rock phosphate, but in view of the 

 fact that the animals would eat but limited quantities of the treated 

 ensilage, and that it was doubtful whether the increase in solubility 

 was due to the ensilage process or to animal digestion, he concluded 

 that this method did not offer a practical means of rendering the 

 phosphoric acid of raw rock phosphate available for agricultural 

 purposes'. 



In a laboratory investigation on the effect of phosphates and 

 sulphates on soil bacteria Fred and Hart^ found that the addition 

 of such materials to a soil in soluble form increased the ammonifi- 

 cation, carbon dioxide evolution, and total number of bacteria. 

 While these effects were much less marked in the case of a rela- 

 tively insoluble phosphate (bone ash), the suggestion that the in- 

 crease in yield resulting from phosphate applications is due in part 

 to the promotion of bacterial activity, which in turn increases ammo- 

 nification (or the supply of available nitrogen) and also the carbon 

 dioxide content of the soil, seems reasonable. The latter compound 

 is effective in bringing about the solution of a further quantity of 

 phosphate mineral. 



Hopkins and Whiting,^ in an article entitled " Soil Bacteria and 

 Phosphates," showed that nitrous acid produced b}^ the action of 

 nitrate bacteria upon ammonium salts dissolved phosphate of lime, 

 the amounts of lime and phosphoric acid in solution increasing as 

 the quantity of oxidized nitrogen increased. These same authors 

 also point out that if all the nitrogen required by standard crops 

 were obtained from the oxidation of ammonia or ammonium salts 

 and the acid thus produced made to act upon rock phosphate the 



iWis. Agr. Expt. Sta. Research Bui. No. 35, pp. 35-66 (1915). 

 «I11. Agr. Expt. Sta., Bui 190, pp. 395-406 (1916), 



