190 GREEN MANURE. 



manure sown. These advantages have led to the 

 assertion that plentiful crops may be obtained with- 

 out any other kind of manure, if, between every 

 two corn crops, green manure is employed. It has 

 been forgotten, however, that this itself will ex- 

 haust the subsoil in the long run. If the subsoil 

 be very rich in fertilizing substances, the surface- 

 soil may be kept in full vigor for many years by 

 green manures, without the assistance of dung ; 

 nevertheless, under any circumstances, it will be 

 useful to manure occasionally, employing such sub- 

 stances as gypsum, common salt, bone-dust, wood 

 ashes, etc., which will be useful both to the crop 

 for manure, and to that which is to follow it. 



" He who wishes to obtain all possible advantage 

 from green manure must observe — first: those 

 plants only must be used whose seed is very cheap. 

 Second : those must be taken which are sure to 

 succeed and grow very fast, in order that in the 

 shortest time the greatest amount of herbage may 

 be produced. Third : they must not contain sub- 

 stances which would be injurious to the succeeding 

 crops. Fourth : they should be deep-rooted plants, 

 for such will absorb the nourishing? substances hid- 

 den in the earth, and convey them to the surface 

 for the use of the shallow-rooted crops. We are 

 not required, however, to confine ourselves to an- 

 nual plants ; on the contrary, it is much better (as 

 will be seen hereafter) if perennial plants are sown, 



