EXPERIMENT STATION BULLETINS. 



441 



Stations, have shown conclusively that the continued use of phosphorus 

 on the land is a safe, sane and business like operation as measured by the 

 increase in yield of the crops grown and the effect upon the soil. The 

 lime content of the soil is not markedly changed by the use of either acid 

 phosphate or bone meal. Inasmuch as raw rock phosphate or "floats" 

 sometimes contains appreciable quantities of carbonate of lime, its use 

 results in the lessening of the so-called acid or sour condition. Our 

 investigations on the solubility of soils that have been treated with certain 

 phosphates indicate that their presence decreases the rate of solubility 

 of some of the mineral constituents and thus reduces the losses due U 



leaching. 





Figure 3. — Wheat responds to phosphorus. On the right typical heads of wheat grown 

 on untreated soil, on the left heads of wheat grown on the same soil treated with 

 200 pounds of acid phosphate. 



Now with respect to the effect upon the tilth of the soil it is doubtless 

 true that as a result of their application there is a tendency toward an 

 improvement of the soil on account of the increase of the vegetable matter, 

 if care is taken to conserve it. Of course, if rotation of crops and proper 

 tillage are not practiced and the manure and crop residues not returned 

 to the land the tilth of the fine textured soils will be impaired but not 

 necessarily to greater extent with the fertilizer than without it. 



Amount to Apply. The amount of phosphate fertilizer to apply to the 

 soil depends upon the carrier and the kind of crops grown and the nature 

 of the soil. The law of diminishing returns should always be considered, 

 that is to say a small application of a phosphate fertilizer results in a 



