COMPOSITION AND FERTILITY OF THE SOIL. 25 



to Caircl, ^* by examples taken, first, in the natural state 

 of pasture, and secondly, in similar soils after treatment. 

 The maximum of fertility in the natural state is a rich 

 pasture capable of fattening an ox and two sheep on an 

 acre. Such soils are exceptional, though in most counties 

 they are to be met with .... The minimum of fertility 

 may be exemplified by a bleak mountain pasture, where 

 ten acres will barely maintain a small sheep. 



The artificial maximum or minimum which results 

 from the treatment of soils of the same quality is more 

 instructive, and may be clearly exemplified by taking two 

 of the experiments which have been carried on by Mr. 

 Lawes of Rothamsted for the last thirty years. Con- 

 fining the comparison to the average of the last twelve 

 years, the following was the weight in pounds of an 

 average crop : — 



Corn, 

 lbs. 



Wheat, grown continuously, without manure 730 



" " ^' with special manure.. 2,340 



The soils here are exactly similar and in the same 

 field, strong land on clay with a substratum of chalk. 

 The management is the same, in so far as culture is con- 

 cerned; both crops are kept equally clean and free from 

 weeds; the same seed is used, and they are exposed to the 

 same changes of weather. The only difference is, that in 

 the one case nature has for thirty years been unassisted 

 by manure, and in the other the soil receives every year 

 the various kinds of manure which have been found most 

 suitable to the crop. The result of this treatment is a 

 return of three times the weight of corn and four times 

 the weight of straw, for an expenditure of manure which 

 leaves a profit of one hundred per cent, on its cost. In 

 both cases the wheat is grown continuously year after year. 



Exhaiistiou of Fertility.— The effect of continued 

 2 



