30 Practical Farming 



soil to be used over again in furnishing plants with food. 

 In addition to the fossil phosphorus in the rocks we get 

 phosphorus from the bones of dead animals of the present 

 day, which thus quickly return it to the soil to grow more 

 plants and to feed more animals; for, as we have seen, 

 without phosphorus no plant can grow, and vdthout plants 

 no animals could live on the earth. Thus the mineral 

 kingdom suppHes food to the vegetable and the vege- 

 table to the animal, and the succession of Hfe is main- 

 tained. 



While analysis shows that there is an immense deposit 

 of the various essential plant foods in the soil, it has also 

 been proved in practice that continual cropping depletes 

 some of these faster than others, and that one of the most 

 rapidly used-up elements is phosphorus. While, as we 

 shall see hereafter, we can get nitrogen in abundance with- 

 out applying any to the land, our older cultivated soils 

 may need application of phosphorus and potassium in the 

 forms of phosphoric acid and potash for the perfection of 

 crops, even when a chemical analysis would show these 

 abundant in the soil. For often they become available 

 too slowly for the demands of modern farming. It has 

 been found, too, that the plants that help us get nitrogen 

 from the air can do this far more effectively when well 

 supplied with phosphorus and potassium. Lime added 

 to the soil plays, as we have seen, an important part in 

 the nitrification of organic matter, and it also assists in 

 bringing into use the insoluble potash in the soil. If 

 carelessly used it may aid in the robbing of the soil. But 

 the use and abuse of lime will be treated in a subsequent 

 lesson. 



