Januaey 7, 1916] 



SCIENCE 



21 



order tliat those who are not familiar with the 

 data in the technical publications may form 

 an intelligent opinion regarding the merits of 

 the several theories proposed regarding the 

 origin of these spots. 



The term " niter spots " has recently been 

 applied by Headden^ to alkali accumulations in 

 certain western soils which develop spots of a 

 dark brown color. Formerly alkali soils were 

 classified as white and black alkali, depending 

 upon the presence or absence of color. The 

 black color of the black alkali spots is due, as 

 shown by Hilgard, to the presence of sodium 

 carbonate, which has a solvent and decompos- 

 ing action upon the organic matter in the soil. 

 The white alkali consisting largely of the sul- 

 phate and chloride of sodium, having no 

 solvent and decomposing action on the organic 

 matter, does not produce any color. There is 

 also an intermediate condition where the color 

 of the alkali spot is a dark or light brown. In 

 these so-called " niter spots " there are two 

 main points which differentiate them from 

 either the white or black alkali soils : (1) the 

 accumulation of large quantities of nitrates; 

 (2) the presence of a brown instead of a black 

 color. The soil of these spots always contains 

 large quantities of the sulphates and chlorides 

 of sodium, potassimn, magnesium and calcium. 

 A discussion has arisen regarding the source 

 of the nitrates and color of these special alkali 

 spots. 



Three theories have been presented regard- 

 ing the origin of the nitrates in these spots. 



(1) Hilgard,^ who first observed the accumu- 

 lations of nitrates in certain alkali spots in 

 arid soils, attributed them to the more rapid 

 nitrification of the organic matter in the warm 

 arid soils when the moisture factor was re- 

 moved by the application of irrigation water. 



(2) Headden* believes them to be due to the 

 fixation of atmospheric nitrogen by the non- 

 symbiotic bacteria, notwithstanding the fact 

 that these bacteria have no power to produce 

 nitrates. Sackett,^ apparently, adopts both the 



2 Headden, Colorado Exp. Sta. Eul. 155. 



3 Hilgard, ' ' Soils, ' ' p. 448. 



4 Headden, Colorado Exp. Sta. Bui. 155. 

 S'Saekett, Colorado Exp. Station Bui. 179. 



above views. He evidently assumes that the 

 nitrogen is fixed by azotobacter or other non- 

 symbiotic organisms and later nitrified by the 

 nitrifying organisms. (3) Stewart and 

 Greaves,^ and later Stewart and Peterson,'^ 

 believe the nitrates are due to the leaching and 

 concentrating action of the irrigating water 

 upon the nitrates occurring in the shales and 

 sandstones (or country rock) adjacent to and 

 underneath the affected areas from which the 

 soil has been derived. 



It is imperative to obtain a clear conception 

 regarding the origin of these acciunulations 

 for two important reasons: (1) Considerable 

 valuable land is being rendered non-productive, 

 due to these enormous accmnulations, and 

 methods of reclamation must await proper con- 

 ception regarding their origin. If the nitrate 

 accumulations are the result of the concentra- 

 tion of the salts preexisting in the country 

 rock proper methods of drainage, adapted to 

 the peculiar soil formation will be effective 

 in reclamation of the soil of the affected area. 

 On the other hand, if the accumulations are 

 due to the abnormal activity of the non-sym- 

 biotic bacteria, drainage is not only not effec- 

 tive in the reclamation of these lands but actu- 

 ally detrimental, since it makes more favor- 

 able the conditions for such bacterial activity. 

 If the later conception is true, investigations 

 must be undertaken to devise methods for 

 checking the abnormal activity of the non- 

 symbiotic bacteria. (2) Dr. Hopkins says: 



To increase or maintain the nitrogen and or- 

 ganic matter of the soil is the most important 

 practical problem of American agriculture. 



If conditions in certain irrigated soils of the 

 arid west are such as to bring about such an 

 abnormal fixation of atmospheric nitrogen as 

 to render the soil non-productive, due to the 

 production of enormous amounts of nitrates, 

 it is important that the conditions governing 

 such fixation may be clearly understood in 

 order that advantage may be taken of this 



6 Stewart and Greaves, Utah Exp. Sta. Bui. 114, 

 1911. 



T Stewart and Peterson, Utah Exp. Sta. Bui. 

 134, 1914; Jr. Am. Soc. Agron., Vol. 6, 241. 



