448 NATURE AND PEOPERTIES OF SOILS 



247. Sodium nitrate (NaNO^ +)-^ — Sodium nitrate is 

 mined in Chile, occurring as a crude salt (caliche) in the 

 semiarid regions along the coast. It is found near the sur- 

 face under an over burden of varying thickness. The cal- 

 iche contains, besides sodium nitrate, such salts as NaCl, 

 K2SO4, NagSO^, and MgSO^ besides traces of Na^COg, K2CO3, 

 and boron. The refined salt, which is shipped to this country, 

 carries from 2 to 3 per cent, of NaCl and KNO3. Its am- 

 monium content is generally rated at about 18 per cent. 



The fertilizer appears on the market in clouded crystals of 

 a yellowish cast, extremely soluble in water and quite de- 

 liquescent. The fertilizer is generally alkaline to litmus. 

 In the soil it diffuses rapidly and is immediately avail- 

 able to plants. For this reason it is extremely valuable early 

 in the spring before nitriiS-cation is active. 



The long-continued use of sodium nitrate will tend to pro- 

 duce an alkaline residue of sodium carbonate in the soil.^ 

 This is due to the absorptive power of the soil for sodium and 

 the ease with which the nitrate ions are lost in drainage. The 

 plant, by using large amounts of nitrates, intensifies this se- 

 lective absorption. 



The origin of the caliche deposits is problematical. The 

 theory has been advanced that the origin is due to the de- 

 composition of great deposits of seaweed on an uplifted con- 

 tinental shelf. Another hypothesis would have the deposits 

 originate from wind-carried guano dust. As rational a the- 

 ory as any is proposed by Singewald and Miller,^ who believe 

 the nitrates were leached from the Andes Mountains and 



^ Fertilizer materials are never pure salts. The plus after tlie formula 

 indicates the presence of impurities. 



^ Hall, A. D., The Effect of the Long Continued Use of Sodium Nitrate 

 on the Constitution of the 801I; Trans. Chem. Soc. (London), Vol. 85, 

 pp. 950-971, 1904. Also, Brown, B. E., Concerning Some "Effects of Long- 

 Continued Use of Sodium Nitrate and Amino^num Sulfate on the Soil; 

 Ann. Eep. Pa. State Coll., 1908-1909, pp. 85-104. 



^Singewald, J. K, and Miller, B. L., Genesis of the Chilean Nitrate 

 Deposits; Econ. Geol., Vol. II, pp. 103-313, 1916. 



