MANURING AND WORN-OUT SOILS 327 



mineral plant foods potash and phosphoric 

 acid and there are many soils that are ex- 

 hausted of these. Fertilisers and manures must 

 be used to make good this loss. But he did 

 mean that a majority of the soils that now pro- 

 duce unsatisfactory crops, and are said to be 

 "worn out," need the humus that comes from 

 decaying plants more than mere additions of plant 

 food. This practice is becoming a noteworthy 

 feature of American farming. 



HOW HUMUS BENEFITS THE SOIL 



Humus benefits the soil in several ways. Its 

 greatest benefit is in improving texture. Mix a 

 little leaf mould, gathered from the woods, with 

 a pailful of light, sandy soil ; it gives the soil more 

 "body," and makes it less leachy. Add leaf 

 mould to a pailful of stiff clay soil that clods, 

 bakes and cracks in the field; the clay be- 

 comes more porous and works up better. Wet it 

 and it does not puddle. These same results farm- 

 ers secure, on a commercial scale, in their fields. 



The relation of good texture to the fertility of 

 cloddy land lies in the uselessness of the clods. 

 The root hairs of plants feed on the outside of the 

 smallest particles of soil. If, therefore, a large 

 proportion of the soil is lumpy and in bad heart 

 the feeding area or "pasturage" is reduced that 

 much. This is why we hear about plant food 

 being "locked up" in lumps it is where the 

 plants cannot get to it. This is why it is said, 

 and truly, "Fining the soil may be equivalent to 

 fertilising it." One way of fining the soil, and 

 hence of increasing its productive power, is to im- 

 prove the texture by adding humus. 



