PRINCIPLES OF MANURING. 45 



3. The ossonti;il materials for vegetable growth that the soil and 

 air can always furnish in abundance are oxygen, hydrogen, carbon 

 and iron, sulphuric acid, lime and magnesia being very seldom 

 wanting. So long as only minute quantities of silica and chlorine 

 are needed we have no occasion to fear but that any soil will meet 

 all the possible demands that can be made for those substances. 

 Inexhaustible stores of carbon exist in the air and in decaying 

 vegetable and animal matter, oxygen and hydrogen are as free as 

 water, while it would be utter nonsence to purposely' put iron iu a 

 fertilizer. 



4. The substances that plants most often have need to hunger 

 after are nitrogen, phosphoric acid, and potash. A "run out" soil 

 may Inck one, two or all of these in an available condition, but a 

 soil is seldom found that fails in any other materials. 



5. The main reason why sulistances called manure cause an 

 increase of crops is that they contain all or part of these valuable 

 ingredients, nitrogen, phosporic acid and potash. This is true of 

 both conmiercial and fai'ra manures. 



6. The chief value of any manure depends upon what it contains 

 of these last mentioned substances. It is not a question of bulk, 

 color, odor, or any other condition save the one mentioned that 

 chiefly determines the value of manures. Remove these three ingre- 

 dients wholly from any manure and it would be of ver}' little value. 



7. One farmer manufactures better manure than another simplj- 

 because his cattle are so fed that larger quantities of nitrogen, phos- 

 phoric acid and potash are found in it. A manufactures better 

 phosphates than B because he causes them to contain more phos- 

 phoric acid in an available form. , 



Means by Which a Soil Becomes Barren or Run Out. 



Soils become run out by continuous cropping without the subse- 

 quent return to them of the materials that the plants have removed, 

 especially niti'ogen, phosporic acid and potash. The same weight 

 of diflerent crops does not remove the same number of pounds of 

 these valuable ingredients. The removal of a ton of wheat impover- 

 ishes the land much more than the removal of a ton of sugar l)eets. 

 The following table shows quite n(>arly the quantities of nitrogen, 

 phosphoric acid and potash contained in a ton of the various 

 productions, that a farmer in Maine would be likel}' to sell from his 

 farm. The figures are taken from a German book, "Fraktische 

 DUngerlehre," written by Dr. Emil Wolff. 



