108 [Senate 



to decrease in fertility, provided each successive growth of plants is 

 removed. But if suffered to remain on the soil, in most cases they 

 enrich it, especially if buried beneath the surface before decay has 

 dissipated their fertilizing parts. A continual turning-under of green 

 crops perpetually increases fertility, for all which the plants abstract- 

 ed from the soil itself, with all they received from the air superadded, 

 is given to it again. But in most of the operations of the farm, the 

 crop is removed ; hence the necessity of making a return in the form 

 of manure, to prevent an increase of sterility. 



2. Another principle is, that plantSj at different periods of their 

 growth, exhaust the soil unequally. As a general rule, during their 

 early growth, and while in a green state, they impoverish the soil but 

 slightly ; but during the ripening of their seeds, they make a heavy 

 draught upon it. Hence, pasture, which is consumed on the ground 

 jn a green state, injures the soil much less than grass cut for hay, after 

 the seeds become fully ripe. Flax, though usually a severe crop, is 

 far less so when removed while in a green and growing state. 

 A striking illustration is also given in case of the turnep, which, 

 though one of the heaviest crops in weight and bulk, produces 

 but slight injury to the soil ; but when it remains on the ground the 

 second year, and ripens its seeds, it has a powerfully exhausting in- 

 fluence. 



3. Different plants do not exhaust in the same manner, nor in equal 

 degree. Some imbibe from the earth much larger portions of certain 

 ingredients than others. Thus, red clover requires a considerable 

 quantity of sulphate of lime or gypsum, which is found largely in its 

 stems by chemical analysis, and which consequently greatly benefits 

 it, when deficient in soil, by application as manure. Grain crops, on 

 the other hand, usually require a liarge supply of silicates, while the 

 nettle and the sun-flower are benefited by nitrate of potash or nitre. 

 Hence, a continual succession of the same crop may soon deprive the soil 

 of certain parts essential to its growth, and languish for the supply, while 

 other succeeding crops requiring different food, may flourish luxuriantly. 



Different plants, too, may feed from different depths of the same 

 Boil. Some of the grasses occupy only a few inches of the surface j 

 while red clover and lucerne are known, sometimes, to send down 

 roots to the depth of three feet, or more. Hence, after some 

 may cease to obtain nourishment from the surface, others may obtain 

 supplies from a greater depth. But this consideration is of compara- 



