468 NATURE AND PROPBETIBS OF SOILS 



a reaction tends to encourage soil acidity, injurious influ- 

 ences may easily occur on soils already acid or possessing only 

 small quantities of active calcium and magnesium. If sulfur 

 functions as a fertilizer, it is by a change to the sulfate, in 

 which form it is absorbed by plants. 



263. The use of sulfate sulfur. — The experimental evi- 

 dence regarding the direct fertilizer influence of sulfate sulfur 

 is much more difficult to interpret than that regarding flowers 

 of sulfur. Gypsum has been applied to soils for centuries 

 and marked influences on crop growth are of common observa- 

 tion. Whether this stimulation is due to the sulfate or to the 

 base which accompanies it cannot be determined. Even if the 

 sulfate influence could definitely be proved, there would still 

 remain the question as to whether the action was direct or 

 indirect. 



264. Relation of sulfur to soil fertility. — The possible 

 deficiency of sulfur in arable soils was first established by 

 Hart and Peterson.^ They point out that crops remove more 



Table XCVII 



pounds sulfur trioxide and phosphorus pentoxme 

 removed to the acre by average crops. 



Crop and Yield to the Acre 



Wheat (30 bu.) 



Barley (40 bu.) 



Oats (45 bu.) 



Corn (30 bu.) 



Alfalfa (9000 lbs. air dry) .... 



Turnips (4657 lbs. air dry) 



Cabbage (4800 lbs. air dry) 



Potatoes (3360 lbs. air dry) 



Meadow hay (2822 lbs. air dry) 



Pounds to the Acre 



S03 



PA 



15.7 



21.1 



14.3 



20.7 



19.7 



19.7 



12.0 



18.0 



64.8 



39.9 



92.2 



33.1 



98.0 



61.0 



11.5 



21.5 



11.3 



12.3 



* Hart, E. B., and Peterson, W. H., Sulfur Bequirements of Farm Crops 

 m delation to the Soil and Air Suppli/; Wis. Agr. Ex|v Sta., Bes. BuL 

 U, 1911. 



