360 INVESTIGATION BY CULTURE EXPERIMENTS 



almost pays for the minerals the first year, the residual effect 

 upon the other crops is to nearly double their total value. 



TABLE 59. ROTATION CROPS ON AGDELL FIELD, ROTHAMSTED 

 Average per Acre of Third 2o-year Period, 1888 to 1907 



In this system the minerals have paid for themselves and made 

 a net profit of 140 per cent on the investment. They have 

 also fully maintained the average yield of legumes, wheat, and 

 turnips since 1852, but the system fails to maintain the supply 

 of nitrogen, and because of this the barley has markedly de- 

 creased in yield. 



One may assume with reasonable confidence that if the turnip 

 leaves, the wheat and barley straw, the bean straw, and perhaps 

 part of the clover crop, had been returned to this land to furnish 

 nitrogen and decaying organic matter, the barley yields might 

 also have been maintained and the turnip crops kept equal to that 

 of 1848, thus providing a permanent system; whereas, under the 

 system practiced, it seems certain that the yield of turnips must 

 decrease in time; and in the opinion of the author the nitrogen 

 supplied by the legume residues will ultimately be insufficient to 



