CHAPTER XIII 



GENERAL MANURES ANIMAL AND VEGETABLE 



General Manures. Consideration of the general 

 manures has been postponed to the second place simply 

 on account of their greater complexity. The arrange- 

 ment has no reference to their relative importance as 

 compared with the special manures. * The latter, as a 

 rule, contain only one fertilising constituent, and their 

 virtue depends entirely upon their chemical composition. 

 The former are complete manures, i.e., they contain 

 phosphates, nitrogen and potash, and the mechanical 

 effects produced by some of them are nearly as impor- 

 tant as those due to the fertilising ingredients. They are 

 all of organic origin and consist of waste animal or vege- 

 table matter, or a mixture of the two. Those which 

 consist entirely of animal matter are generally the most 

 concentrated and most active. Those which consist of 

 vegetable matter are more bulky and decompose more 

 slowly, but produce greater mechanical effects. The 

 mixed products, to which farmyard manure belongs, are 

 less concentrated than the jfirst, but are often nearly as 

 active, and their mechanical effects are often greater 

 than those of the purely vegetable manures. 



ANIMAL MANURES GUANOS. 



Introduction of Guanos. The discovery of guano was 

 the immediate cause of what has amounted to a great revo- 

 lution in modern agriculture. Its fertilising properties 



