OF PLANTS BY MANURING. 69 



The rapidity, then, with which a manure will ex- 

 ert its action on the soil depends upon the facility 

 wdth which it passes into decay, or becomes soluble 

 in the ground. The slower this process, the slower 

 will its operation also be. Dry weather, heavy soil, 

 and a coarse or compact condition of the manure, 

 retard its decay and liquefaction, and accordingly its 

 working, just as the opposite circumstances acceler- 

 ate them. On this account, manuring substances 

 when dissolved always operate more promptly than 

 when solid. If a substance is wholly insoluble, and 

 remains so in the ground, it excites no action, even 

 when composed of the most powerfully fertilizing 

 elements. This we see illustrated in the various 

 kinds of coal, which are often very rich in nitrogen, 

 and yet exert no forcing power, inasmuch as they 

 continue lying in the earth without undergoing lique- 

 faction or decay. On the other hand, the most active 

 manuring elements may do injury instead of benefit, 

 if applied in too strong or too concentrated a form ; 

 and this will occur when the manure decays and de- 

 liquesces rapidly, and finds but little moisture in the 

 soil to dilute it. Drainings when applied to fields in 

 dry weather burn up vegetation, but when mixed 

 with water, or thrown upon moist soils, do not pro- 

 duce this effect; guano and rape-dust strewed too 

 near the seed not unfrequently destroy its germinat- 

 ing power, whilst this injury does not occur when 

 they are mixed with earth, or harrowed into the 

 ground before the time of sowing. 



