186 FARM-TAED MA^'URE. 



nishes. After a consecutive series of remunerative crops of 

 corn, turnips, and clover, these plants ^vill thrive no longer 

 in the same field. 



Since, then, the presence of decaying organic remains 

 in the soil does not, in the slightest degree, prevent or 

 arrest its exhaustion by cultivation ; it is impossible that 

 an increase of those substances can restore the lost capa- 

 city of a field for production. In fact, when a field is 

 completely exhausted, neither boiled saw-dust, nor salts 

 of ammonia, nor both combined, will impart the power 

 of yielding the same series of crops a second and third 

 time. When these substances improve the physical con- 

 dition of the ground, they exert a favourable influence 

 upon the produce ; but, after, all, their ultimate effect is 

 to accelerate and complete the exhaustion of the soil. 



But farm-yard manm-e thoroughly restores to the soil 

 the power of producing the same succession of crops a 

 second, a third, and a hundredth time : where it is 

 apphed in proper quantities it will ftdly cure the state 

 of exhaustion, and often make a field more fertile than 

 it ever was before. 



The restoration of fertility by farm-yard manure can- 

 not be attributed to the mixture of combustible mate- 

 rials (salts of ammonia and the substance of decaying 

 saw-dust): for if these had a favoiurable effect, it must 

 have been of a subordinate khid. The action of farm- 

 yard manure most undoubtedly depends upon the incom- 

 bustible ash-constituents of the plants which it contains. 



In farm-yard manure the field actually receives a cer- 

 tain quantity of all the mineral ingredients which have 

 been removed in the crops. The dechne of fertihty was 

 in proportion to the removal of mineral constituents ; the 

 renewal of productiveness is in proportion to their 

 restoration. 



