112 



BULLETIN No. 145 



[April, 



TABLE 16 ORGANIC PHOSPHORUS: RATIOS OF CARBON TO ORGANIC PHOS- 

 PHORUS, NITROGEN TO 1 ORGANIC PHOSPHORUS, CARBON To NITROGEN 

 IN SURFACE Son, 



(b) PHOSPHORUS ASSOCIATED WITH THE MATIERE NOIRE 



Of the two available methods for determining 1 the organic 

 phosphorus, the one, the determination of the phosphorus associ- 

 ated with the matier e noire extracted from the soil by 4 percent 

 ammonia, has given rise to some confusion. Grandeau (10) re- 

 garded the phosphorus extracted with the matiere noire as being 

 probably in organic combination. Eggertz (21), Nilson (79), 

 Wiklund (25), Dumont (65), Ladd (43) and Snyder (41) also 

 regarded it as organic in form. Pitsch (14) and Van Bemmelen 

 (23) took the opposite view. Pitsch thought that part of the ex- 

 tracted phosphorus may have been derived from the inorganic 

 phosphates of the soil. Van Bemmelen regarded the phosphorus 

 precipitated with the matiere noire as absorbed phosphorus. Quite 

 recently, Fraps (69) concluded that only 1/3 of the phosphorus ex- 

 tracted by ammonia was in organic combination, while still later 

 Stoddart (80) concluded that only 1/5 of the extracted phosphorus 

 was in organic combination. As a result of this conflicting evi- 

 dence there is considerable confusion regarding 1 the nature of the 

 phosphorus extracted by ammonia. One cause of this confusion, 

 no doubt, is the difficulty of getting rid of the suspended clay, 

 ordinary filtration will not remove it. Obviously all of the phos- 

 phorus associated with the suspended clay should not be included 

 with the organic phosphorus, altho part of it may be organic in 

 form. Fraps removed the clay by precipitation with ammonium 

 sulfate. There is no evidence, however, that this reagent does 

 not also precipitate some organic matter either chemically or me- 

 chanically. Ammonium sulfate is used by physiological chemists 

 to precipitate the proteins in order to make certain group separa- 

 tions, while some preliminary work here showed that complete 

 saturation of the ammoniacal extract of the soil with ammonium 

 sulfate, after the removal of the suspended clay, produced a heavier 

 qualitative precipitate of organic matter than did the addition of 

 hydrochloric acid. It would seem, therefore, that the evaporation 

 method of Hampton and Mooers (77) is more desirable for the 



