68 DEPARTMENT OF AGRICULTURE GEORGIA. [354] 





ist learns what they contain, and in what ratio the different 

 elements enter into their composition. 



2d. By experiments in growing plants under circum- 

 stances in which all the conditions of growth are known, 

 and in which the effect of different elements of plant* food 

 can be definitely ascertained. Indeed, plant analysis, soil 

 analysis, and experiment, are all employed i.i conjunction, 

 to ascertain the needs of different plants. 



Seeds are planted in soils of known composition, to 

 which different elements of plant-food, in vaiious quanti- 

 ties and ratios, are added, and the results compared. 



Science is thus enabled to know, not only what kinds of 

 food are required for different agricultural plants, but the 

 proportions in which they unite in each. 



By reference to the Tables in the Appendix, it will be 

 seen that in the ash of most of our cultivated plants, 

 potash and phosphoric acid play a conspicuous part. 



Not only do these enter largely into the ash of these 

 plants, but it is a well established fact that they are earlier 

 exhausted from the soil than any other mineral elements, 

 and hence must be supplied artificially by the farmer. 



These, together with nitrogen, are the principal constitu- 

 ents necessary to be artificially supplied on most soils, 

 though soda and lime are often applied with satisfactory 

 results. 



As shown by the Tables, tobacco is a large consumer of 

 all of the principal elements of mineral plant-food, and is, 

 consequently, the most exhausting crop grown in the 

 South. While the analysis of plants indicates very accu- 

 rately the kind and per cent, of the constituents which 

 enter into the organism, a knowledge of the character of 

 the soil, and feeding capacity of the plants, is necessary to 

 determine to what extent these constituents should be 

 artificially applied. 



In plant fertilization, the farmer aims to supply each crop 

 with just those constituents in kind and quantity which 



