Loess Soils of the Transition Region 3 



Considerable work, also, was done during the course of this 

 research, with a view to determining which are the most satisfac- 

 tory and practical methods for the determination of the above- 

 mentioned soil-constituents, under different conditions. 



METHODS USED IN THE DETERMINATION OF HUMUS, NITROGEN AND 

 HUMUS NITROGEN 



Before beginning the investigation of the humus and humus 

 nitrogen content of the soils of the Transition Region, taken at 

 various depths, it was necessary to select methods which would 

 give reliable results, as well as be reasonably economical of time. 

 Before finally selecting a method for the gravimetric determina- 

 tion of humus, three methods were taken into consideration, viz., 

 the " Official " method, which is the method of the Association of 

 Official Agricultural Chemists of the United States, the method 

 devised and used by Hilgard, and the method worked out by 

 Rather, which is a modification of the " Official " method. Some 

 surface soil from the Nebraska Experiment Station farm was 

 taken as a standard and this was used in all cases. The " Offi- 

 cial " method was discarded after a very brief trial, as it was 

 found, as had'been previously reported by others, to give results 

 which are unreliable ; it has been proven on numerous occasions 

 that the results obtained by the " Official " method are very high, 

 often several times as high as the results obtained by a " Hilgard " 

 determination on the same soil, the latter method having been 

 generally accepted as one which gives reasonably accurate and de- 

 pendable results. 



THE OFFICIAL METHOD 



The " Official " method is carried on as follows : The soil sam- 

 ple, usually lo grams, is placed in a filter and washed repeatedly 

 with I per cent, hydrochloric acid until the washings show no 

 precipitate when treated with ammonium hydrate and ammonium 

 oxalate. This treatment extracts all lime and magnesia, which, 

 if present, would prevent the humus going into solution in the 

 later treatment with 4 per cent, ammonium hydroxid. The acid 

 is then removed by repeated washings with distilled water, using 



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