222 THE SYSTEM OF FARM-YAftD MANURING. 



which existed in the deeper layers, and was brought up 

 by the clover or the turnips. But the high returns of 

 corn given by a field do not necessarily decline with the 

 incipient failure of the clover ; for where the arable 

 soil of a field has, after every rotation, received from the 

 clover or turnips more corn-constituents than it had 

 lost by the corn-crop, there may be a gradual accumu- 

 lation of an excess of these elements of food sufficient to 

 conceal altogether from the farmer the true condition of 

 his land. By introducing into his rotation vetches, white- 

 clover, and other fodder-plants that derive their food 

 from the upper layers of the soil, he succeeds in keeping 

 up his live stock, and he indulges in the notion that all 

 things go on in his field just as before, when the clover 

 or the turnips yielded good crops. This is of course 

 simply a delusion, as there is no longer an actual re- 

 placement of the loss sustained. His high corn-crops 

 are now gained at the expense of the nutritive sub- 

 stances accumulated in excess in the arable surface soil 

 which are set in motion by the fodder-plants introduced 

 into the rotation, and are uniformly distributed again 

 in the arable soil after each rotation, by means of the 

 farm-yard manure. 



His dung-heap may happen to be of larger bulk and 

 extent than formerly, but as the-re is now no further 

 supply of nutritive substances brought up from the sub- 

 soil or the deeper layers by the clover or turnips, the 

 power of the manure to restore the original fertility of 

 the arable soil is continually decreasing With the 

 ultimate consumption of the excess of corn-constituents 

 accumulated in the arable soil, the time comes when 

 the corn-crop begins to diminish, whereas the produce 

 of straw is comparatively higher than before, as the 

 conditions for the formation of straw have been steadily 

 increasing. 



Of course, the farmer cannot fail to remark the 

 diminution of his corn-crops, which induces him to have 

 recourse to drainage, to improved tillage, and to the 

 substitution of other cultivated plants, in lieu of clover 

 and turnips. If the subsoil of his fields will permit it, 



