PLANT-FOOD AND AGRICULTURE. 225 



supplied to the plant by superphosphate, is an exact equivalent to 

 a pound of soluble phosphoric acid supplied to the plant by dung, 

 and so with the other elements. That it is an incorrect reasoning 

 which compares dung, in its effects, which is a furnisher of a com- 

 plete plant-food, with a single fertilizer which contains but one 

 element of plant-food. The true criticism of fertilizers for general 

 use must be based on their containing plant-food of all the kinds 

 required by our crops : the true comparison must be between 

 dung and a complete fertilizer. 



Our numbered facts, however, indicate an application of a fertil- 

 izer which cannot fail of success in growing our crops, even in 

 competition with dung. If it is kept in mind that plant-food is 

 plant-food, irrespective of source of supply, it cannot fail to be 

 apprehended that crops may be successfully grown by the appli- 

 cation of either dung or fertilizer of the proper kind, and that the 

 conditions of success must rest on the methods we practice to 

 bring our food within reach of the plants, and in that form which 

 will enable them to be appropriated by the plant. 



The first essential to success must be in the use, the continued 

 use, of a complete fertilizer in the quantity required by our crops. 

 This fertilizer may be either dung or a mixture of chemicals, which 

 shall contain the needed constituents. If we use dung, we apply 

 similar proportions of plant-food to all our crops, because the com- 

 position of the dung depends not on what we desire, but upon the 

 material upon which the animals have been fed who have pro- 

 duced it. It is a waste product of our barn economy. We mean 

 nothing derogatory in this term, but simply the expression of a 

 fact, a fact notwithstanding the leading importance of this product 

 in our farm operations. In a chemically complete fertilizer we 

 have a manufactured article in which the elements of the dung are 

 present, and grouped according to the needs of our plants. We 

 here reduce the chances of loss to a minimum, and escape the 

 possibly injurious effect of an excess of one element producing a 

 growth we do not calculate upon or desire. 



These are practical and theoretical views combined, and it less- 

 ens not their importance that New England farmers usually use 

 their dung for crops which they feed out and convert into dung. 



Let us see now, what we may expect reasonably, in accordance 

 with our numbered propositions, from a complete manure. 

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