168 FIRST PBINCIPLES OF AGRICULTURE. 



meal and wheat middlings, valuable food products, which 

 contain practically equivalent amounts of total digestible 

 food, and which usually cost about the same price per 

 ton: — 



POUia)8 OF 



, Nitrogen. Phosphoric Acid. Potash. 



One ton of Com Meal contains ... 33 14 8 



One ton of Wheat Middlings contains .50 28 14 



Excess in Middlings 17 14 6 



That is, by the exchange of one ton of com meal for one 

 ton of wheat middlings, there is not only no loss of fertil- 

 ity, but a gain in mineral constituents nearly equivalent 

 to that contained in one ton of the corn meal. The use of 

 tables in the Appendix will enable the student to make 

 correct comparisons of the fertility values of the chief 

 farm crops and purchased feeds. 



Manurial Value. — The direct fertilizing value of a 

 ton of feed is, however, greater than the manurial value of 

 the same; since, in feeding, a portion of the fertilizing 

 constituents is retained in the animal itself or obtained 

 in animal product, the amount depending upon the kind 

 of animal, and the object of feeding. 



The quantity of nitrogen and ash constituents voided in 

 the manure of a grown animal, neither gaining nor losing 

 in weight, will be nearly the same as that contained in 

 the food consumed. In case animals are increasing in size, 

 producing young, or furnishing milk or wool, the nitrogen 

 and ash constituents in the manui-e will be less than in the 

 food, in direct proportion to the quantity of these sub- 

 stances which have been converted into animal products. 



The data secured in experiments by Lawes & Gilbert, 

 at Rothamsted, England, contained in the following table, 



