Commercial Fertilizers. 167 



been manured with natural products, as stable manure, they 

 may be used singly to force a maximum growth of the crop. 

 Thus, a specific fertilization is arranged for the various rotations, 

 the crop receiving that which is the most useful. There is no 

 doubt that there is a good scientific basis for this system, and that 

 it will work well, particularly where there is a reasonable abund- 

 ance of all the plant food constituents, and where the mechanical 

 and physical qualities of .the soil are good, though its best use is 

 in * intensive' systems of practice. It cannot be depended upon 

 to give good results where the land is naturally poor, or run 

 down, and where the physical character also needs improve- 

 ment." 



Wagner system. "Another system which has been urged, 

 notably by the German scientist, Wagner, is based upon the fact 

 that the mineral constituents, phosphoric acid and potash, form 

 fixed compounds in the soil and are, therefore, not likely to be 

 leached out, provided the land is continuously cropped. They 

 remain in the soil until used by growing plants, while the nitro- 

 gen, on the other hand, since it forms no fixed compounds and 

 is perfectly soluble when in a form useful to plants, is liable to 

 loss from leaching. Furthermore, the mineral elements are rel- 

 atively cheap, while the nitrogen is relatively expensive, and the 

 economical use of this expensive element, nitrogen, is dependent 

 to a large degree upon the abundance of the mineral elements 

 in the soil. It is, therefore, advocated that for all crops and for 

 all soils that are in a good state of cultivation, a reasonable excess 

 of phosphoric acid and potash shall be applied, sufficient to more 

 than satisfy the maximum needs of any crop, and that the nit- 

 rogen be applied in active forms, as nitrate or ammonia, and in 

 such quantities and at such times as will insure the minimum loss 

 of the element and the maximum development of the plant. The 

 supply of the mineral elements may be drawn from the cheaper 

 materials, as ground bone, tankage, ground phosphates and iron 

 phosphates, as their tendency is to improve in character; potash 



