182 SOILS AND FERTILIZERS 



235. Sulfur as a fertilizer. — It has been pointed out that 

 sulfur is one of the substances essential to plant growth, 

 but it has generally been considered that a sufficient quantity 

 is contained in arable soils to supply the needs of crops, 

 and that its application as a fertilizer is unnecessary. In 

 spite of this there have been occasional experiments con- 

 ducted from time to time in which sulfur, usually in the form 

 of flowers of sulfur, has been applied to soils to ascertain its 

 effect on plant growth. 



236. Experiments with sulfur as a fertilizer. — Most of 

 the experiments with sulfur have been conducted in Europe. 

 In some cases the application of sulfur to the soil was found to 

 be beneficial to plant growth, in other cases there was no ef- 

 fect. Where no result was produced, it is reasonable to be- 

 lieve that there was sufficient sulfur in the soil to supply 

 the needs of the plants, and that any further addition was un- 

 necessary. In those experiments in which sulfur was found 

 to exert a beneficial action we cannot be certain that the in- 

 creased plant growth was due to the larger quantity of sulfur 

 obtained by the plants. Sulfur has been found to influence 

 the action of the germs in soils, and it is possible that the 

 plants grew better because the soil nitrogen was converted 

 more rapidly into an available form by the stimulating ef- 

 fect of sulfur on the bacteria concerned in that process. Sul- 

 fur sometimes has other beneficial effects on plant growth. 

 These secondary reactions sometimes lead to erroneous con- 

 clusions regarding the effect of a fertilizer. 



237. Quantity of sulfur contained in crops. — It has been 

 computed from the analyses of various plants that the 

 quantity of sulfur, when figured as sulfur trioxide, that is 

 removed from the soil by crops of ordinary size is sometimes 

 greater, and sometimes less, depending on the kind of crop, 

 than is the quantity of phosphoric acid removed by the same 

 crop. This may be seen in the following table. 



