86 FIELD CROPS FOR THE COTTON-BELT 



cotton in the United States. These soils are extremely 

 deficient in both organic matter and nitrogen. There are 

 at least three important reasons for this. (1) The cropping 

 systems have been such as to return very little organic 

 matter and nitrogen. (2) The open, porous character of 

 these soils hastens the oxidation and destruction of what- 

 ever vegetable matter is applied. (3) The abundant rain- 

 fall of the region together with the porous nature of the 

 soils causes the soluble nitrogen to leach away rapidly. 

 The same conditions also cause much loss of nitrogen on 

 account of erosion. 



This deficiency of nitrogen is also noticeable on much 

 of the clay soils in the cotton-belt. Most of the Houston 

 black clay of north and central Texas, central Alabama, 

 and northeastern Mississippi, has continuously been 

 cropped to cotton until it is nitrogen hungry. Green- 

 manure crops rather than commercial fertilizers should 

 be employed to restore this nitrogen. 



95. Phosphatic fertilizers. Acid phosphate is the 

 material most universally used by cotton growers as a 

 source of phosphoric acid. Other materials of secondary 

 importance are raw rock phosphate, ground bone, and 

 slag phosphate. 



Add phosphate. This is a manufactured product 

 made by treating ground raw rock phosphate, Ca 3 (PO 4 ) 2 

 with an equal weight of sulfuric acid, (H 2 SO 4 ). This 

 results in the replacement of part of the phosphoric acid 

 by sulfuric acid, thus forming monocalcium phosphate, 

 CaH 4 (PO 4 ) 2 , and calcium sulfate, CaS0 4 as the chief 

 constituents: 



Ca 8 (PO 4 ) 2 plus 2 H 2 SO 4 equals CaH 4 (P0 4 ) 2 plus 2 CaS0 4 . 

 Phosphoric acid in the form of tricalcium phosphate is 



