354 THE PRINCIPLES OF SOIL MANAGEMENT 



and hay were all larger on the carbonate -of- lime 

 treated plats. 



224. Sulfate of lime. Gypsum, in which form calcium 

 sulfate is usually applied to soils, is effective in liberating 

 potash, and possibly other substances, from the more 

 difficultly soluble combinations. Its action in improving 

 tilth is less marked than that of caustic lime, or of the 

 carbonate. Whether it eventually contributes to the 

 presence of carbonate of lime is a matter regarding 

 which there is still a difference of opinion. It has the 

 disadvantage of introducing into the soil an acid radical, 

 which is removed by plants only in small amounts, and 

 which tends to produce an acid condition of the soil. 

 On the whole, gypsum is not an adequate substitute for, 

 nor so desirable a form of, calcium as the oxide, hydroxide 

 or carbonate. 



225. Common salt. Sodium chloride has a marked 

 effect upon some soils, but wherein its effectiveness lies 

 is not well understood. The addition of sodium and of 

 chlorine as plant constituents is clearly not the reason, 

 as these substances are always present in soils in avail- 

 able form far in excess of their requirements. 



The effect of sodium chloride upon clay-bearing soils 

 is to liberate certain plant nutrients, among which are 

 calcium, magnesium, potassium, calcium and phos- 

 phorus. This action, although limited in amount, is, 

 in some cases at least, partly responsible for the bene- 

 ficial action of common salt. 



The structure of the soil is improved by the applica- 

 tion of sodium chloride, just as it is by lime, although 

 usually not to the same extent. 



