cultivates not solely to kill weeds and admit warmth and air into 

 the soil, but to encourage the growth of bacteria, as well as 

 the distribution and conservation of soil moisture. 



"The Sap of the Soir' 



We frequently hear farmers speak of the "sap of the soil" — 

 a phrase which expresses a great deal. All cultivated plants 

 take up their food in dilute solution. The sap of a tree or 

 plant circulates throughout its system of trunk, branches and 

 leaves, carrying with it the nourishment necessary for its up- 

 building, as does the blood in animals. This sap has been 

 absorbed from the soil through the roots of the plant, and is 

 charged more or less with plant food ingredients which were 

 either appHed in a soluble form or were rendered soluble through 

 bacterial action in the soil, or through the digestive process 

 which takes place in contact with the roots of plants. Manure 

 or commercial fertilizers enrich the sap of the soil by supplying 

 additional quantities of available plant food. Bacteria, as we 

 have seen, help to break down the organic forms of plant food 

 and render them soluble for the sap of the soil to absorb. 



Potential Fertility 



Plant 

 Food 

 Locked Up 



Chemistry teaches us that plants are composed of certain 

 fixed elements which are supplied by the soil and the air. It 

 further teaches that while there is an abundant supply, yet 

 we have exhausted the three leading elements, nitrogen, phos- 

 phoric acid and potash in available forms; that so-called 

 barren or unproductive soils may be rich in plant food elements, 

 but that these elements are so locked up as to be of little value 

 to the commercial farmer, whose chief concern is quick crops for 

 quick returns. In other words the available plant food (nitro- 

 gen, phosphoric acid and potash) has been exhausted, leaving 

 only the unavailable or what is known as the potential fertility, 

 which, by the slow processes of nature, is yielded up too slowly 

 to be depended upon by the commercial farmer. 



It has been known for a long time that practically all 

 tillable soils are rich in all plant food elements, and yet many 

 of them are barren and most of them will not produce profit- 



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