526 SOILS: PROPERTIES AND MANAGEMENT 



445. Sulfur as sulfate. There is less experimental 

 evidence regarding the effect of sulfur in the form of 

 sulfate on plant growth than there is for the free sulfur. 

 The fact that the bases with which .the sulfate is com- 

 bined are likely to have an effect on plant growth, makes 

 the accumulation of proof by experimentation a somewhat 

 more difficult matter. That there may be a possible de- 

 ficiency of sulfur in arable soils has been pointed out by 

 several investigators, including Hart and Peterson l in 

 this country. They point out that crops remove more 

 sulfur from the soil than was shown by the early deter- 

 minations of sulfur in plant ash, from which a large part 

 of the sulfur was volatilized during the process. They 

 then proceed to calculate the sulfur removed by a num- 

 ber of crops on the basis of their own methods and 

 compare this with the phosphorus in similar crops. 



POUNDS SULFUR TRIOXIDE AND PHOSPHORUS PENTOXIDE 

 REMOVED TO THE ACRE BY AVERAGE CROPS 



1 Hart, E. B., and Peterson, W. H. Sulphur requirements 

 of farm crops in relation to the soil and air supply. Wise. 

 Agr. Exp. Sta., Research Bui. No. 14. 1911. 



