88 FIELD CROPS FOR THE COTTON-BELT 



rich in organic matter, it will furnish the cotton fanner 

 a very much cheaper source of phosphoric acid than acid 

 phosphate. Raw rock phosphate contains from 28 to 30 

 per cent of phosphoric acid. 



96. Need of cotton soils for phosphoric acid. — The 

 need of phosphatic fertilizers in the production of cotton 

 is almost universal on the Norfolk, Orangeburg, and Sus- 

 quehanna soils comprising the greater part of the Atlantic 

 and Gulf Coastal Plain region. Analyses have shown 

 much of these soils to contain less than 200 pounds of 

 phosphoric acid to the acre. (For such a calculation the 

 depth of the soil is considered to be seven inches.) 



A permanently profitable system of agriculture can 

 never be established on these soils without the more or 

 less continued use of phosphate fertihzers. The riph 

 alluvial soils of the Mississippi River and the Houston 

 black clays of Texas, Alabama, and Mississippi, con- 

 stitute the most important cotton soils that are not at 

 present considered to be in need of phosphatic fertilizers. 



Experience has taught that practically all of the sands 

 and sandy loam soils and much of the upland clays in the 

 cotton-belt, except the arid section of west Texas, are 

 benefited by the application of phosphates. 



97. Potassic fertilizers. — There are three materials 

 that "furnish the potash in cotton fertilizers. These are 

 kainit, muriate of potash, and sulfate of potash. Of these 

 three, kainit is most largely used. Experiments have not 

 shown that a pound of potash in kainit, when applied to 

 cotton, is more effective than an equal amount in muriate 

 or sulfate of potash. The farmer should buy the material 

 in which he can get the potash cheapest. 



Kainit is a low-grade material containing approxi- 

 mately 12 per cent of potash, largely in the form of sulfate. 



