203] 1'^^ FERTILITY OF THE COMMON FIELDS 4^7 



sufficient replacement of the phosphates taken from the soil, 

 the yield of wheat was so low that the amount of phosphoric 

 acid removed was small, and the system was permanent for 

 all practical purposes. One of the facts given in substantia- 

 tion of this view is that the yield after enclosure increased 

 considerably/ 



In discussing these points, it will be well to begin with 

 the evidence as to exhaustion afforded by the increased yield 

 under enclosure. The improvement in yield took place be- 

 cause of the long period of fallow obtained when the land 

 was used as pasture; or, in the eighteenth century, with the 

 increase in nitrogenous organic matter made possible when 

 hay and turnips were introduced as field forage crops. That 

 is, the increase in yield depended either upon that prolonged 

 period of recuperation which will restore fertility, or upon 

 an actual increase in the amount of manure used. Appar- 

 ently, then, open-field land had become exhausted, since an 

 increase in yield could be obtained by giving it a rest, with- 

 out improving the methods of cultivation, etc., or by adding 

 more manure. 



There was not, as Dr. Russell supposes, enough manure 

 under the medieval system of husbandry to maintain the fer- 

 tility of the soil. It is true that the husbandman understood 

 the value of manure, and took care that the land should re- 

 ceive as much as possible, and that he knew also of the value 

 of lime and marl. But, as Dr. Simkhovitch says : 



It is not within our province to go into agrotechnical details 

 and describe what the medieval farmer knew, but seldom prac- 

 ticed for lack of time and poor means of communication, in 

 the way of liming sour clay ground, etc. Plant production is 

 determined by the one of the necessary elements that is available 



2 Ihid., pp. 48-52. 



