112 2 THE BOOK OF GARDENING. 



soda, magnesia, lime, iron, silica, &c, combined with sulphates, 

 phosphates, and nitrates. 



Then, again, manures are spoken of as "general manures" 

 when they contain all the necessary elements for plant-growth ; 

 or "special manures," when they only supply one or several of 

 these elements. 



These elements, again, are said to be "dormant," "latent," or 

 "active," according as they are insoluble or soluble in plant- 

 juices, which exude from the rootlets, or in soil-water, and are 

 thus made available for plant-food, or are locked up in an inert 

 form in the soil. In fact, a very large part of the elements of 

 plant-food contained in soils is present in such a condition that 

 plants are unable to make use of it. For example, it is very 

 usual to find about o'i5 per cent, of phosphoric acid in an 

 ordinary garden soil. Such a soil cjin. deep, in its dry state, 

 may be said to weigh from 1200 to 1500 tons per acre. A 

 soil containing C15 per cent, of phosphoric acid would 

 accordingly contain somewhere about two tons of phosphoric 

 acid to the acre, disregarding the subsoil altogether. Such a 

 soil contains as much phosphoric acid per acre as would be 

 contained in about seventeen tons of superphosphate, or in nearly 

 ten tons of bone-meal; and yet the addition of a few hundred 

 pounds of phosphatic manure, may make the difference between 

 a full crop and a bad one. Similar statements would apply to 

 other constituents of the soil. This leads the gardener to 

 recognise the important fact that it is not the total proportion 

 of phosphoric acid, or potash, or of nitrogen, that rules a soil's 

 fertility for horticultural purposes, but the amount of each of 

 them that is present in an immediately available condition. 



Manures for the garden, for practical purposes, may be 

 considered as nitrogenous, phosphatic, potassic, or calcareous 

 fertilisers, according as nitrogen, potash, phosphoric acid, or 

 lime is the predominating ingredient. 



Farmyard and Stable Manure. 



This substance differs from all artificial manures, and in 

 several important particulars. Its value depends, first, on the 

 materials of which it is formed; secondly, on the condition of 

 its formation; and, thirdly, on the way it has been kept and 

 treated until it is applied to the soil. 



The materials of farmyard or stable manure are litter and the 

 excreta of animals. That produced from young growing stock, 

 or from milch cows, is not so good as that produced from old' 

 or fattening animals. Then, again, that which is produced from 

 underfed animals is of a very inferior description. Further, the 

 composition of the excreta of domestic animals of various kinds 

 is different. The excrements of horses which are fed with a more 

 nitrogenised food than most other animals of the farm, are of a 



