FERTILIZER PRACTICE 569 



4. Physical condition of the soil. The addition of lime 



and organic matter, the utilization of drainage, 

 tillage, and the like, all are conducive to higher 

 crop returns through the indirect effect on fertilizer 

 efficiency. 



5. Lime. Lime, by improving physical conditions, 



by setting plant-food free, by correcting acidity, 

 by stimulating bacterial action, and by tending 

 to eliminate toxic materials either directly or 

 indirectly, is of great importance in fertilizer 

 practice. In fact, certain fertilizers, such as 

 ammonium sulfate and acid phosphate, do not 

 reach their full efficiency unless plenty of lime is 

 present. 



6. Organic matter. Besides the effect of organic matter 



on physical conditions and chemical reactions 

 which indirectly influence fertilizer action, an im- 

 portant action is set up by organic matter in the 

 encouragement of bacterial functions. As the 

 favorable changes of fertilizers, especially those 

 carrying nitrogen, is due to biological activity, 

 the presence of organic materials becomes doubly 

 important. 



7. Chemical composition of the soil. Since the full 



return from a fertilizer is derived when the ele- 

 ments are well balanced, the actual constitution 

 of the soil becomes a factor, especially when ready 

 availability is obtainable. Therefore, in choosing 

 a fertilizer and deciding on the amounts to apply, 

 the chemical condition of the soil is no mean factor. 



While the conditions affecting fertilizer efficiency have 

 thus been so briefly disposed of, it is evident that a more 



