380 NATURE AND PROPERTIES OF SOILS 



ditions of contact between the soil and the gypsum were ab- 

 normal. McMillar * found that the potash of certain Minne- 

 sota soils treated with one per cent, of gypsum was appre- 

 ciably influenced three months after the application. When 

 gypsum has proven beneficial to crop growth, the effect may 

 have been due to the nutrient influence of the sulfur it con- 

 tains or to the potash liberated from its soil combinations. 

 The use of gypsum as a soil amendment is now seldom recom- 

 mended, especially if the other forms of lime are available. 



Sodium chloride has a marked effect on the productivity of 

 some soils, especially when certain crops such as asparagus 

 are grown. Wherein its effectiveness lies is not well under- 

 stood. Increased fertility arising from the addition of sodium 

 and chlorine, which are plant constituents, is probably not 

 the reason of its influence, as these substances are usually 

 available in soils far beyond any possible plant requirement. 

 When common salt shows a beneficial influence, it is probably 

 due to its tendency to liberate certain mineral nutrients such 

 as potassium, calcium, and magnesium. Since it tends to 

 leave an acid residue in the soil and since some form of lime 

 will generally give better and more permanent results, the 

 use of common salt is not recommended except in certain 

 cases. 



The use of di-calcium silicate (Ca 2 Si0 4 ) in an experimental 

 way as a liming material has recently received some attention. 

 Cowles, 2 in 1917, presented data from which he concluded that 



1 McMillar, P. R., Influence of Gypsum upon the Solubility of Potash 

 in Soils; Jour. Agr. Res., Vol. XIV, No. 1, pp. 61-66, 1918. 



Morse, F. W., and Curry, B. E., The Availability of Soil Potash in 

 Clay and Clay Loam Soils; N. H. Agr. Exp. Sta., Bui. 142, 1909. 



Bradley, C. E., The Eeaction of Lime and Gypsum on Some Oregon 

 Soils; Jour. Ind. and Eng. Chem., Vol. 2, No. 12, pp. 529-530, 1910. 



Briggs, L. J., and Breazeale, J. F., Availability of Potash in Certain 

 Orthoclase-b earing Soils as Affected by Lime or Gypsum; Jour. Agr. 

 Res., Vol. VIII, No. 1, pp. 21-28, 1917. 



a Cowles, A. H., Calcium Silicates as Fertilizers. Metal. Chem. Eng., 

 Vol. 17, pp. 664-665, 1917. 



