SOME GENERAL PRINCIPLES 39 



gen in the soil is by no means equal, but up to the 

 present time it would seem correct to say that rela- 

 tive capability in all of these has not yet been defi- 

 nitely ascertained. With reference to the whole 

 question much has yet to be learned, but it is now 

 certain that in all, or nearly all, instances in which 

 clovers are grown on land, they leave it much richer 

 in nitrogen than it wa;s when they were sown upon 

 the same. 



They also add to the fertility of the surface 

 soil by gathering plant food in the subsoil below 

 where many plants feed. They have much power to 

 do this, because they are deep rooted and they are 

 strong feeders; that is, they have much power to 

 take up food in the soil or subsoil. Part of the 

 food thus gathered in the subsoil helps to form roots 

 in the cultivable area and part aids in forming top 

 growth for pasture or for hay. If grazed down 

 or if made into hay and fed so that the manure goes 

 back upon the land the fertility of the same is in- 

 creased in all leading essentials. This increase is 

 partly made at the expense of the fertility in the sub- 

 soil. But the stores of fertility in the subsoil are 

 such usually as to admit of thus being drawn upon 

 indefinitely. 



Clovers improve soils mechanically by rendering 

 them more friable, by giving them increased power 

 to hold moisture, and by improving drainage in the 

 subsoil. Of course, they have not the power to do 

 this equally, but they all have this power in degree 

 and in all the ways that have been named. 



Clovers send down a tap root into the soil and 



