2IO 



SOILS AND FERTILIZERS 



per acre. Such soils, however, should be more thor- 

 oughly cultivated, and manured with farm manures, to 

 make the phosphates available. There is frequently 

 an apparent lack of phosphoric acid when in reality the 

 trouble is due to other causes, as a deficiency of lime or 

 organic matter to render the phosphates available. Be- 

 fore using phosphate fertilizers, careful field tests should 

 be made to determine the needs of the soil. 



242. How to keep the Phosphoric Acid Available. - 

 Phosphoric acid associated with organic matter in a 

 moderately alkaline soil is more available than that in acid 

 soils. Soft phosphate rock may be mixed with manure or 

 material like cottonseed meal and made slowly available 

 for crops, but where land is high in price such a pro- 

 cedure is not economical. Soils which contain a good 

 stock of phosphoric acid, when kept well manured and 

 occasionally limed if necessary, have a liberal supply 

 of available phosphoric acid. The following is an 

 example of two soils from adjoining farms, which 

 have been cropped and manured differently. 31 



