298 



SOIL CONDITIONS AND PLANT GROWTH 



TABLE LXXX. NITRATES IN CROPPED AND UNCROPPED SOILS AT ROTHAM- 

 STED EXPRESSED AS N., Ib. PER ACRE. RUSSELL (24i/). 



climatic factors seem to be ruled out. In 1905 Waring- 

 ton showed that the amount of nitrate in the drainage waters 

 from Broadbalk field was -considerably less than was ex- 

 pected from the manure supplied and the crop reaped. He 

 thought that denitrification might account for some of the 

 discrepancy but not for all, as it could hardly be supposed to 

 act in dry summer weather ; he further suggested that the 

 nitrate might be taken up by the plant and then somehow 

 lost before harvest. More recently Lyon and Bizzell (183) 

 found more nitrate on land cropped with maize (after allowing 

 for the nitrogen present in the crop) than on fallow land of 

 similar history, and concluded that the growing maize plant 

 in some way stimulated nitrification. During the latter part 

 of the life of the plant less nitrate was found in the cropped 

 than in the fallow land, and the further conclusion is drawn 

 that nitrification is, inhibited by the conditions accompanying 

 the decreasing activities of the roots. On the other hand, 

 where oats and potatoes were grown the nitrates were never 

 so high in the cropped as in the uncropped land, again, 

 apparently, after allowing for what has been absorbed by the 

 crop. The following amounts of nitrogen as nitrate occurred 

 in parts per million of soils are given in Table LXXXI. : 



