18171 SOILS PEBTILIZERS. 423 



low concentrations of dried blood such as are used in the field were employed, 

 active nitrification took place in every case, and when equal amounts of nitrogen 

 were added it was found that the yield of nitrate was quite similar whether 

 the nitrate had been derived from dried blood, bone meal, or ammonium sul- 

 phate. High concentrations of bone meal furnishing amounts of nitrogen 

 equivalent to that supplied by 1 per cent of dried blood inhibited nitrification 

 in the same way as the dried blood. It was found that the inability to nitrify 

 1 per cent of dried blood was not confined to any one type of soil nor to soils 

 low in organic matter. 



" The effects produced by the addition of alkali salts varied greatly when 

 different concentrations of nitrogenous materials were employed. In a given 

 soil a concentration of 0.05 per cent of sodium carbonate was distinctly toxic 

 to the nitrification of 1 per cent of dried blood, while as high a concentration 

 as 0.4 per cent produced no effects on the nitrification of 0.1 per cent of dried 

 blood. Likewise, 0.1 per cent of sodium carbonate was toxic to the nitrification 

 of 0.15 per cent of ammonium sulphate, and markedly stimulating when 0.0625 

 per cent of ammonium sulphate was used. Similar statements may be made 

 with regard to the effects of sodium sulphate. 



" The results al.so show that widely different conclusions may be drawn from 

 laboratory experiments when different periods of incubation are used. 



" Nitrites were found to accumulate in large amounts where excessive 

 amounts of nitrogenous materials were employed. In some cases the nitrite 

 content greatly exceeded the nitrate content after an incubation period of 

 sevei-al weeks. Likewise, the addition of alkali salts may suppress nitrate 

 formation, while at the same time permitting nitrite formation to proceed 

 actively." 



The author concludes as a result of these investigations " that the methods 

 now employed by many students of nitrification, in which high concentrations of 

 nitrogenous materials are added and the nitrate determined at a fixed interval 

 of time, are not only unsatisfactory, but that the results thus obtained are likely 

 to be more misleading than informing." He therefore recommends that the 

 activities of nitrifying organisms be studied in an environment as nearly similar 

 to that of the field as possible. 



A bibliography of literature bearing on the .subject is given. 



The nitric nitrogen content of the country rock: A contribution regarding 

 the origin of niter spots in certain western soils, R. Stewaet and W. Peter- 

 son (Soil Sci., 2 (1916), No. 4, pp. 3^5-361, pi. J ) .—Experiments conducted at 

 the Utah Experiment Station with samples of Utah and Arizona soils are 

 reported, from which results were obtained similar to those obtained in previous 

 work (E. S. R., 32, p. 28) with Utah, Colorado, and Wyoming soils. 



It is concluded that " the nitrates of the niter spots of the cultivated soils 

 are derived from the preexisting accumulations occurring in the adjacent 

 country rock and transported by the movement of underground water, brought 

 to the surface by exposure of the rock outcrop, and there deposited by the evap- 

 oration of the water. The brown color of the niter spots is due to the solvent 

 and decomposing action of the nitrates on the old organic compounds of the soil, 

 the source of which, like the nitrate, is in the shale and sandstone of the area, 

 which is coal and oil bearing." 



It is further pointed out that " characteristic niter spots may be produced 

 artificially in the laboratory vsith a rich greenhouse soil and an excess of sodium 

 nitrate. They are produced equally as well in soil rendered sterile by treat- 

 ment with a saturated solution of mercuric chlorid or 5 per cent solution of 

 carbolic acid." 



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