jp/o] 



CARBON, PHOSPHORUS AND NITROGEN IN SOILS 



111 



It will be observed that from 1/4 to 2/5 of the total phos- 

 phorus of the several soil types considered is in organic combina- 

 tion. These results indicate that a larger amount of phosphorus 

 is in organic combination than the work of some American inves- 

 tigators would lead us to believe. 



2. CHEMICAL 



(a) ANALYTICAL, RKSUL/TS OF SOIL FROM ILLINOIS SOUTH 



FARM 



A sample of soil for a study of the organic phosphorus, by the 

 available methods for the determination of the organic phosphorus 

 of the soil, was obtained from the Illinois South Experimental 

 Farm. This soil is the ordinary brown silt loam soil of the corn 

 belt. 



The total potassium, carbon, nitrogen, and phosphorus in the 

 surface and subsoil were determined by the methods adopted by 

 the Illinois Experiment Station. The results, expressed as pounds 

 per two million pounds of dry soil, will be found in Table 15. The 

 average potassium content of 36,700 pounds, and 37,070 pounds in 

 the surface and subsoil indicate a constant mineral composition, 

 hence the calculation method may be safely applied for the deter- 

 mination of the organic phosphorus. The amount of organic phos- 

 phorus, the various ratios and the developed factor will be found 

 in Table 16. It will be seen that 46 percent of the total phosphorus 

 in this soil is in organic combination. 



TABLJE; IS. ANAI,YTICAI, RESUI/TS OF Soil, FROM ILLINOIS SOUTH KXPF.RI- 

 MENTAI, FARM: RESULTS EXPRESSED AS POUNDS IN Two MILLION 

 POUNDS OF DRY Soil, 



*L/ater inspection of the strip of land from which this sample was taken led to the conclu 

 sion that it may have been modified by a previous disturbance of the soil in putting- in tile 

 drainage; and a composite sample was subsequently collected at points a short distance from 

 the tile drain which showed 985 pounds of phosphorus instead of 919 pounds. The possible 

 influence of this difference should be kept in mind. Thus the percent of total phosphorus in 

 org-anic form would be reduced from 46 percent to 43 percent. C. G. Hopkins. 



