92 THE ESSENTIALS OF AGRICULTURE 



tenfold more plant food than all the commercial fertilizers used 

 in a year. Little attention is given to the care of this manure, 

 and in the country as a whole nearly half of it is wasted. Next 

 to the waste of the soil itself, this is probably the greatest waste 

 on American farms. 



99. What is manure? Any material which contains con- 

 siderable quantities of more or less available nitrogen, phos- 

 phorus, or potassium, and which is added to the soil for the 

 purpose of increasing crop yields, is called a manure or fertilizer. 

 Such materials usually are not applied in sufficient quantities to 

 supply the entire needs of the crop, but enough is applied to sup- 

 plement the available plant food already in the soil. Farm manure, 

 commonly called barnyard manure, is derived from the farm 

 itself, as the manure from farm animals or the refuse from crops. 

 Commercial fertilizers are those sold on the general market and 

 consist of concentrated and soluble forms of the three elements 

 of plant food nitrogen, phosphorus, and potassium. 



100. Value of barnyard manure. The value of barnyard 

 manure is the plant food it contains, the organic matter 

 which it supplies to the soil, and the beneficial action its 

 presence exerts upon the soil organisms. The plant food in 

 manure comes from that taken from the soil by the crops. 

 When crops are fed to animals, approximately three fourths 

 of the nitrogen, phosphorus, and potassium goes with the 

 manure and may be returned to the land. These plant foods 

 are then in a form to become quickly available through decay 

 of the manure. 



101. Value of manure from different animals. The value of 

 manure when the feed remains the same depends upon the 

 kind and age of the animals by which it is made. Growing ani- 

 mals take more nitrogen from their food for the production of 

 muscle and more phosphorus for the production of bone than 

 grown animals that are at work or that are merely fattening. 



102. Value of manure per one thousand pounds live weight 

 of animals. In the following table the values are based on 

 the amount of the principal elements of plant food present in 



