46 THE ENCLOSURES IN ENGLAND [202 



unsatisfactory. Much calcium carbonate is also lost during the 

 process: and when this constituent falls too low, the soil be- 

 comes " sour " and unsuited for crops. 



The simplest system of husbandry is that of continuous wheat 

 cultivation, practiced under modern conditions in new countries. 

 When the virgin land is first broken up its fertility is high ; so 

 long as it remains under cultivation this level can no longer be 

 maintained, but rapidly runs down. During this degradation 

 process considerable quantities of plant food become available 

 and a succession of crops can be raised without any substitution 

 of manure . . . After a time the unstable period is over and the 

 new equilibrium level is reached at which the soil will stop if 

 the old husbandry continues. In this final state the soil is often 

 not fertile enough to allow of the profitable raising of crops ; 

 it is now starving for want of those very nutrients that were 

 so prodigally dissipated in the first days of its cultivation, and 

 the cultivator starves with it or moves on. 



Fortunately recovery is by no means impossible, though it 

 may be prolonged. It is only necessary to leave the land cov- 

 ered with vegetation for a period of years when it will once 

 again regain much of the nitrogenous organic matter it has lost.^ 



'Dr. Russell adds that soil-exhaustion is essentially a mod- 

 ern phenomenon, however, and gives the following reasons 

 for supposing that the medieval system conserved the fer- 

 tility of the soil. First, the cattle grazed over a wide area 

 and the arable land all received some dung. Thus elements 

 of fertility w^ere transferred from the pasture land to the 

 smaller area of tilled land. This process, he admits, in- 

 volved the impoverishment of the pasture land, but only very 

 slowly, and the fertility of the arable was in the meanwhile 

 maintained. Secondly, the processes of liming and marling 

 the soil were known, and by these means the necessary cal- 

 cium carbonate was supplied. Thirdly, although there was in- 



1 E. J. Russell, The Fertility of the. Soil, Cambridge, 1913, pp. 43-46. 



