230 THE SYSTEM OF FAKM-YARD MAMJEING. 



the subsoil (which is to the clover or turnips what the 

 arable siu-face soil is to the cereals), suffering a continued 

 drain upon its stores of phosphoric acid, potash, hme, 

 magnesia, &c., begins to lose its productive power for 

 clover or turnips ; and thus the nutritive substances, 

 taken away from the arable surface soil in the corn crops, 

 are no longer replaced from the store 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 dechne ^vith the incipient faihu^e 

 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 accumulation 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, wliite-clover, 

 and other fodder-plants that derive their food from the 

 upper layers of the soil, he succeeds in keeping up his 

 hve 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 replacement of 

 the loss sustained. His high corn- crops are now gained 

 at the expense of the nutritive substances accumidated 

 in excess in the arable surface soil wJiich 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 mamu-e. 



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

 extent than formerly, but as there 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 



