28 



In conclusion they say 



these five samples of soil are really the same soil under long- continued 

 treatment of different kinds. It is not improbable that work on widely differ- 

 ent soils will show even much greater variations than those here noted. 

 The work shows, however, that even in such cases there is a difference in 

 the nitrogenous compounds in the soil, and that different decompositions of 

 the nitrogenous matter has taken place and probably will continue to take 

 place, under the different conditions imposed upon the soils in the field. 



A very interesting study has been made by Shmook (1914) 

 of the nitrogen distribution in four Russian soils, one of the Podzol 

 type, two of the Chernozem type, and one of the Laterite type by 

 applying the method of Hausmann (1899). The water extract 

 from 100 grams of the Podzol soil showed a very high content of 

 soluble nitrogenous compounds. This amounted to 0.0452 gram 

 of nitrogen which constituted 19.10 per cent of the total soil nitro- 

 gen. This was distributed as follows : amide nitrogen 0.0034 

 gram, di-amino nitrogen traces, and mon-amino nitrog-eia 0.0408 

 gram. These results were deducted from the analyses of the 

 hydrolyzed soil. Thirty gram samples of soil were hydrolyzed 

 with 120 cc. of hydrochloric acid (sp. gr. 1.12) for 8 hours and 

 the analysis carried out as directed. 



He finds, that the Chernozem and Podzol soils show a simi- 

 larity in the distribution of amide nitrogen, and that of the amino 

 acid nitrogen, but that the nitrogen distribution in the Laterite 

 soil is entirely different from the other types. He concludes that 

 the amount of protein in the soil is not in direct relation to the 

 amount of organic matter, and that the nitrogen insoluble in hydro- 

 chloric acid occurs in unknown form and composes only 1.50 to 

 1.90 per cent of the organic matter of the Chernozem and Podzol 

 soils, but 13.70 per cent of the total organic matter of the Laterite 

 soil, after subtraction of the protein nitrogen belonging to this 

 insoluble portion. He suggests that these results would indicate 

 that the organic nitrogen existed in the soil in large part as protein 

 material in the Chernozem and Podzol soils, but that a considerable 

 portion was of a non-protein origin in the Laterite soil, since 

 the amount of this insoluble "melanin" in pure proteins amounts 

 to from 0.60 to 1.80 per cent of the total protein nitrogen.* 



Potter and Snyder (1915 a) made a study of some Iowa soils 

 using Van Slyke's (1911) method of protein analysis. Their soils 

 were the same type but had received different fertilizer treatment. 

 At the same time they also made a study of peat soil. The soils 

 were in all cases first extracted with 1 per cent hydrochloric acid 

 "in order to render the humus more soluble." They were then 

 hydrolyzed by boiling one part of the soil with two parts of 22 

 per cent hydrochloric acid for forty-eight hours. They also pre- 

 pared a 1 per cent sodium hydroxide extract of the acid leached 

 soils, and after precipitation with sulfuric and acetic acids the 

 resulting humic acid precipitate was subjected to the above method 

 of analysis. 



The authors conclude: (1) that the humin nitrogen as deter- 

 mined by the Van Slyke method on soils extracted by dilute alkali 



*Actually in some cas^s these results are much lower, and in others de- 

 cidedly Higher, e . gr., Van Slyke (1911) finds gelatin contains 0.07 per cent and 

 fibrin 3.17 per cent. 



