The Function of Manures and Fertilizers 21 



NATURAL MANURES AND ARTIFICIAL FERTILIZERS 



Farmyard manure, and many other natural products, 

 possess this second function in a marked degree, and 

 the indirect manurial value of these is due largely to 

 the good effect that the substances associated with the 

 nitrogen, phosphoric acid and potash in them exert in 

 increasing the crop. This good effect is observed in two 

 directions. First, the vegetable matter contained in 

 the natural manure improves the physical character of 

 soils those that are clayey and compact, by making 

 them more open and porous, separating the particles, so 

 that the water and air can penetrate more freely, and 

 thus act directly upon the dormant or insoluble constit- 

 uents that are contained in it; and those that are light 

 and sandy, by filling up the open spaces, thus making 

 them more compact. In the second place, the addition 

 of vegetable matter to soils, even though it contains no 

 essential constituents, improves it by enabling it to more 

 readily and completely absorb and retain not only the 

 water, but also the soluble essential constituents that 

 may be added. The chief distinction between what are 

 known as manures and what are known as fertilizers 

 is the difference in respect to this secondary function. 

 The manure possesses the two functions, the one to supply 

 the essential constituents, and the other to assist plant 

 growth by aiding in the improvement of those already 

 contained in the soil, and this latter function it exerts in 

 a marked degree ; while the fertilizer, as a rule, possesses 

 but one, namely, that of furnishing plant-food. The 

 indirect effect of the materials associated with the con- 

 stituents in artificial fertilizers is seldom very useful, and 

 sometimes may be harmful. 



