PHOSPHATES 79 



clay soils or soils containing considerable organic matter and 

 potash. Organic matter tends to promote fermentations which 

 attack the phosphates and make them available as plant food, 

 and with the aid of potash, it tends to act upon the lime of the 

 phosphates. The kind of crop also influences the rate of de- 

 composition of phosphates. Some plants are more able to make 

 use of the phosphoric acid of phosphates than others.* 



