316 DRAINING. 



854. Green manures, which contain but little 

 nitrogen, may also be used very advantageously 

 together with urine and similar animal substances, 

 which soon bring them into a state of decomposition. 

 A similar effect is also produced by steeping these 

 matters in the ammoniacal liquor of the gas-works 

 (154, 886) ; the whole of the vegetable matter is soon 

 reduced to a pasty decomposing mass, which is a very 

 good manure. 



855. The dry and less changeable kinds of vegeta- 

 ble matter are chiefly valuable for their mechanical 

 effects, the influence which they exert upon evapora- 

 tion, and the inorganic matters which they contain; 

 they likewise may, however, be brought into a state 

 of decomposition by the addition of animal matters 

 (802). 



856. The number of inorganic substances employed 

 as manures is very great, and their use is naturally 

 much dependent on the nature of the soil. In many 

 cases, great benefit is derived from mixing soils; 

 either mixing a portion of the subsoil with the sur- 

 face-soil (761), or by adding to the soil earth brought 

 from a distance, and possessing a different nature and 

 composition. 



857. The earthy matters thus added to the soil 

 can hardly be called manures, although in truth they 

 considerably resemble manures in the mode in which 

 they act. By draining, deep ploughing, mixing, and 

 by the use of mineral manures, either the mechanical 



