74 DEPARTMENT OF AGRICULTURE GEORGIA. [360] 



ent in most soils in sufficient quantity to meet all demands 

 for it in the first capacity. 



Phosphate rock and animal bones furnish the chief com- 

 mercial source of phosphoric acid. 



Potash, next in importance to phosphoric acid, is ex- 

 ported from Germany in the two forms of sulphate of pot- 

 ash and chloride of potassium. 



From hard wood ashes it is obtained as carbonate. It is 

 furnished also to soils, by the decomposition of igneous 

 rocks containing felspar. In some instances the debris of 

 these rocks is, in some localities, deposited in vast beds in 

 connection with marl, known as green sand marl. There is 

 a deposit of this marl in Houston, and other counties both 

 east and west of it, which analyzes from two to three per 

 cent, of potash. 



Fwm-yard manure, which is a complete manure in the 

 sense of containing ail of the elements of plant-food, has 

 in all time been used in soil fertilization, and answers an 

 admirable purpose when applied broadcast in large quanti- 

 ties ; but the supply is too limited, especially in a planting 

 region, to accomplish the purpose on a large scale. 



The chief reliance for soil improvement on a large scale 

 must ever be the growth of leguminous plants, to be re- 

 turned to the soil, in connection with the application of the 

 principal mineral elements in conjunction with a judicious 

 rotation of crops, which require the mineral elements in 

 different proportions. 



The plants used in this country for this purpose are 

 clover, the field pea or bean, and common vetch. 



Dr. St. Julien Ravenel, of Charleston, South Carolina, 

 has been conducting some very interesting experiments on 

 the coast lands of his State, in which he applies what he 

 calls the ash element, composed of 500 pounds of cal- 

 cined marl, and 1,000 pounds of ground phosphate 

 rock and 500 of kainft, to peas on cultivated lands, and 

 to vetch on meadows, at the rate of 400 or 500 pounds per 

 acre. 



