232 THE SYSTEM OF FARM-YARD MANURING. 



field permanently richer in nutritive substances than 

 it is by nature, \ve might expect that a course of manur- 

 ing for fifty years would necessarily produce a steady 

 increase in the crops. 



Now, if farmers who practise the system of rotation, 

 laying aside all bias and prejudice, would compare their 

 present with their former crops, or with those obtained 

 by their fathers or grandfathers, none of them would 

 be able to say that the crops have increased, and only 

 few that the average has remained the same. Most of 

 them would find, that on the average, the straw-crops 

 have turned out higher, but the corn-crops lower, and 

 proportionately lower than they formerly were higher ; 

 and that the surplus money which their parents gained 

 by the former high crops, the result of their improve- 

 ments, as they supposed, must now be paid out again, 

 to purchase manuring substances, which, as people 

 formerly thought, could be * produced.' Now, how- 

 ever, they begin to learn that though such substances 

 may be produced for a time, they cannot be reproduced 

 in perpetuity. 



In like manner, the farmer whose richer ground has 

 enabled him to carry out the three-field system, and 

 whose rich meadows guarantee a supply of manure, 

 who obtains as abundant harvests and as large a weight 

 of corn as the farmer who adopts the system of rotation, 

 and thus surmises that his management has procured 

 what the ground gives of its own free will, will inevi- 

 tably discover that his fields may be exhausted of the 

 conditions of their fertility, and that it is quite erroneous 

 to suppose that all the farmer's art consists in convert- 

 ing manure into corn and flesh. 



A simple law of nature regulates the permanence 

 of agricultural produce. If the amount of produce is 

 in proportion to the surface presented by the sum total 

 of nutritive substances, in the soil, the permanence of 

 the crops will depend upon the maintenance of that pro- 

 portion. 



This law of compensation, the replacement of nutri- 

 tive substances which the crops have carried away from 



