190 



PRINCIPLES OF AGRICULTURAL CHEMISTRY 



behavior of the corn crop was closely related to the quantity of 

 active phosphoric acid in the soil. Soils containing 20 parts per 

 million, or less, of active phosphoric acid are clearly deficient in 

 phosphoric acid. Soils containing 30 to 100 parts per million 



Fig. 41. Corn grown with and without phosphoric acid on four soils con- 

 taining less than ten parts per million of active phosphoric acid, Texas Sta. 



were, as a rule, deficient. Soils containing 100 to 200 parts per 

 million were deficient in about one-half of the experiments. 

 AVERAGE CORN POSSIBILITY AND AVAILABILITY OF PHOSPHORIC ACID. 



Active phosphoric acid 



Corn equivalent 

 (bushels per acre) 



The quantity of phosphoric acid withdrawn from the soil was 

 also related to the quantity of active phosphoric acid. In the 



