CHAPTER III. 



MANURES 



The use of manures is, briefly, to supply nutritive matter for 

 encouraging and sustaining plant-growth. They restore the ferr 

 tility of an exhausted soil, and enrich a naturally poor soil. Any 

 substance, therefore, added to the soil which has the power, either 

 directly or indirectly, of increasing its fertility may be considered 

 as a manure. It may contribute directly by supplying what is 

 required, or indirectly by its chemical action on dormant sub- 

 stances already present, but not in a suitable state for being 

 absorbed by the plants. Manures, more especially farmyard or 

 pen manures, may also improve the physical condition of the soil, 

 rendering heavy clay land lighter and more porous, and sandy soils 

 denser and more retentive of moisture. Growth in plants cannot 

 take place without the main constituent parts of which they are 

 composed being extracted from the earth. The continued pro- 

 duction of crops, therefore, necessitates the withdrawal of an 

 enormous supply of certain elements from the soil, and it is evident 

 that if no means be taken to restore the substances thus removed, 

 the soil becomes gradually "exhausted" (see under Soils). Accord- 

 ing to LIEBIG, "the best fertiliser for any particular crop is that 

 which contains the amount of nitrogen, phosphoric acid, potash, 

 etc., which are removed from the soil by a typical good yield of 

 the crop in question." 



The immediate effect of a manure depends, (1) on its solubility, 

 and (2) on the suitability of the plant-food which it contains for the 

 use of the crop or plant it is applied to. Suitable mixtures, made 

 up according to the special need of different crops, usually afford 

 most satisfaction. Manures may be divided into two classes, viz. 

 (1) Organic (or Xatnral) manures, as those composed of vegetable 

 or animal substances ; and (2) Inorganic, or Artificial manures, which 

 are of mineral origin. While most manures act directly by sup- 

 plying the three chief elements of plant-food (nitrogen, potash, and 

 phosphoric acid), certain kinds are of value chiefly on account of 



