106 



BULLETIN No. 145 



[April, 



of soil having a low humus content in a box and set aside for one 

 year. At the end of the experiment the humus was extracted and 

 the carbon and nitrogen determined in the inatiere noire. At first 

 thought this would appear to furnish the desired information, but 

 unfortunately no check was run with the untreated soil, so no cor- 

 rection can be made for the carbon and nitrogen which may have 

 been converted into humus from the unhumified material of the 

 soil. This is evidently not a quantity which can be ignored since 

 the humus content of the original soil is .06 percent while the total 

 nitrogen of the soil is .02 percent showing that considerable un- 

 humified organic matter was present, otherwise the humic nitrogen 

 would be 33.33 percent while it has been shown (71) that the 

 humic nitrogen would more probably be nearer 5 percent. In ad- 

 dition, the fact that the humus obtained from sugar contains some 

 nitrogen is evidence that some of the unhumified organic matter of 

 the soil has been converted into humus, since sugar does not con- 

 tain nitrogen. The results, however, will be found in Table 7. In 



TABI,E 7. MINNESOTA Soil, STUDIES: HUMUS PRODUCTION FROM KNOWN 



MATERIALS 



the first five substances the variation is from i :2i.7 for oat straw 

 to i :4-5 for meat scraps. 



The large number of carbon and nitrogen determinations made 

 in the soils of Illinois (68) rendered it possible to determine the 

 nitrogen-carbon ratio, not only for the surface soil, but also for 

 the subsurface and subsoil. The average of 19 determinations for 

 the soil type, gray silt loam on tight clay, gave the ratios 1 110.4, 

 i :8.8, and 1 17.6 for the surface, subsurface, and subsoil re- 

 spectively. The ordinary brown silt loam soils as an average of 

 68 determinations gave a nitrogen-carbon ratio of 1:12.1, 1:11.5 

 and i :8-9 for the surface, subsurface, and subsoil respectively. The 

 black clay loam soils as an average of 25 determinations gave 

 i 111.7, i :II.Q and i :g respectively in the surface, subsurface, and 

 subsoil. The peat soil as the average result of 5 determinations 

 gave i :ii.8 and i :i2.9 for the surface and subsoil respectively. 



