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CHAPTER VII. 



EFFECT OF CROPPING UPON THE SOIL. ROTATION 

 OF CROPS. 



Effects of cultivation. Composition of ash from the common 

 crops. Differences in the ash from various parts of the same 

 plant. Differences in ash of different crops. How particular 

 classes of substances may be exhausted, and special manures be 

 useful illustration in the use of lime. Bearing of these facta 

 upon theories of rotation in cropping. Necessity of rotations, 

 and care to be exercised in their management. 



SECTION I. ON THE COMPOSITION OF THE ASH FROM OUR 

 COMMON CROPS. 



We are now able to understand the effect of constant 

 cultivation upon the soil. This might indeed, to a 

 certain extent, be gathered from what has already been 

 said in the two preceding chapters; it is necessary, 

 however, that the sketch of such an important part of 

 the subject should be made perfectly clear and precise. 

 The student will by this time know, that as the in- 

 organic part in the seed of the plant consists mostly 

 of those constituents which were shown by Table I. to 

 be least abundant in the soil, the constant selling off 

 of grain must in time very materially decrease the 

 stock of such substances, unless the supply is kept up 

 by the addition of manures. If the soil was very rich 

 at the commencement, exhaustion might be quite slow; 

 but if the stock of fertility was small, it would soon 

 reach the utterly exhausted and worn out condition in 

 which we see so many of our farms. This and other 

 points will be made more clear by a table giving the 

 composition of our most common cultivated crops. 



