i6o CHEMICAL COMPOSITION OF THE SOIL [chap. 



is maintained. A better idea of the requirements of 

 land under ordinary farming conditions may be obtained 

 from a study of certain of the Rothamsted plots, for 

 which a balance-sheet showing the gains and losses of 

 nitrogen over a period of years can be drawn up. 



Taking first the unmanured wheat plot as an ex- 

 ample of land reduced to a very low level of fertility, we 

 learn that during the years 1852 to 1902 it yielded on an 

 average a crop of 13-1 bushels of wheat, which contained 

 in both grain and straw 18 lb. of nitrogen. During this 

 period the percentage of nitrogen in the soil had fallen, and 

 the nitrogen lost by the soil is approximately equivalent to 

 that removed in the crop. At this low level of fertility, 

 then, the nitrogen that had also been removed by 

 drainage and bacterial action (and such losses must 

 exist) had been replaced by recuperative actions, 

 doubtless due to Azotobacter and kindred organisms in 

 the soil. But for the plot receiving farmyard manure 

 every year, the nitrogen removed in the crop together 

 with what has been stored up in the soil only accounts for 

 about one-half of the nitrogen applied as manure. The 

 wasteful actions due to drainage or bacteria must have 

 enormously increased and have removed the balance, 

 any recuperative actions being swamped in such great 

 losses. Turning now to one of the rotation plots on 

 Agdell, we find that when clover or beans were grown 

 once in each four years, and where also the root crop was 

 returned to the land (see Table XV.), the nitrogen in 

 the soil remained stationary despite its removal in the 

 crops of wheat, barley, and clover, or beans. In this case, 

 then, the recuperative actions (which include the growing 

 of a leguminous crop) were able to balance the wasteful 

 processes in the soil and the removal of the grain and 

 clover crops, without any additions of nitrogen from 

 outside the farm. The level of production was not, how- 



