512 EXPERIMENT STATION RECOKD. [Vol.36 



with the time of year were noted. The uitrogen-fixiiig power was lowest in 

 winter and gradually increased through the spring and summer to a maximum 

 In the fall. 



On the basis of these results the author judges these soils to be entirely 

 unsatisfactory with reference to productivity. 



It was further found that the greatest bacterial numbers and nitrogen fixa- 

 tion occurred in a soil growing root crops, while the fallow soil stood nearly the 

 last in both. Conclusions based on these results are considered unsafe. 



The organic matter of the soil. — I, Some data on hum.us, humus carbon, 

 and humus nitrogen, R. A. Gobtneb (SoU Sci., 2 (1916), No. 5, pp. 395-U2, 

 pis. 2, figs. 17). — Experiments conducted at the Minnesota Experiment Station 

 are reported in which " eight mineral soils, three peats, one muck, and five 

 samples of unchanged vegetable materials were selected and analyzed for total 

 carbon and total nitrogen ; for carbon and ' humus ' soluble in 4 per cent NIIiOH 

 both before and after leaching the substances with 1 per cent HCl ; for carbon 

 and nitrogen soluble in 4 per cent NaOH both before and after leaching the mate- 

 rial with 1 per cent HCl ; for carbon and nitrogen extracted by 4 per cent NaOH 

 from the residue remaining after the soil or vegetable materials which, without 

 previous treatment, had been extracted with 4 per cent NaOH and subsequently 

 leached with acid ; for carbon and nitrogen extracted by the addition of water 

 to the residue remaining from the preceding extraction ; and for nitrogen in the 

 1 per cent HCl extract. Colorimetric measurements were also made on the 

 Tarious solutions." 



The results of a comparison of the data obtained are taken to indicate that 

 " the ' humus ' extract of soils and peats is not a typical soil product, formed 

 in the soil by the action of bacteria and fungi, for very similar extracts can be 

 obtained from unchanged vegetable materials. ' Humus ' does not consist en- 

 tirely of a black compound, or compounds, but it also contains a large propor- 

 tion of almost colorless substances, the presence of which is normally masked 

 by the black color. A 4 per cent solution of sodium hydroxid does not extract 

 either the same substances or the same quantity of substances as does a 4 per 

 cent solution of ammonium hydroxid. From a given soil, after leaching with 

 1 per cent HCl, ammonium hydroxid will extract less carbon and at the same 

 time more color than will a sodium hydroxid solution. In general the forms 

 of soil nitrogen appear to be quite similar in solubility to those forms occurring 

 in unchanged vegetable materials, the only noteworthy difference being that 

 vegetable materials contain a very considerable amount of nitrogen soluble in 

 1 per cent HCl while soils contain only a small quantity, and the soils contain 

 an appreciable amount of nitrogen quite insoluble in 4 per cent NaOH, in 

 decided contrast to the unchanged vegetable materials." 



All the mineral soils and the one calcareous peat tested contained a soil 

 pigment which was absent from the unchanged vegetable materials or the acid 

 peats, was intensely black, and contained only a relatively small proportion of 

 the soil nitrogen. 



From the results obtained, it is considered extremely doubtful if a specific 

 " huraification " of plant materials takes place in the soil. 



It is concluded that " the common practice of comparing ' humus nitrogen,' 

 determined in a 4 per cent NaOH extract, with ' humus,' obtained by 4 per cent 

 NHiOH, can give only meaningless results. ... A determination of the 

 ' humus ' as ordinarily carried out appears to be wholly without scientific 

 justification. The European method of reporting ' humus ' by making a deter- 

 mination of total organic carbon appears to be far preferable." 



Thirty-one references to literature bearing on the subject are cited. 



