138 



SOIL CONDITIONS AND PLANT GROWTH 



the crop. The following amounts of nitrogen as nitrate occurred in 

 parts per million of soils : 



TABLE LVIII. NITROGEN AS NITRATE IN CROPPED AND UNCROPPED SOILS, 

 ITHACA, N.Y. (LYON AND BIZZELL). PARTS PER MILLION. 



It is interesting to observe that the figures are generally of the 

 same order as at Rothamsted excepting only in July and August, 

 1908. We have never observed, however, any increase in nitrate on 

 cropped land such as is recorded in their maize experiments ; our 

 results with wheat and barley have always shown a decrease, like 

 theirs with oats. Leather's experiments also show a decrease. 

 (167^). The nitrate in the drainage water from the fallow gauges 

 at Pusa contained respectively 261*5 an< ^ 209*6 Ib. per acre during the 

 period 1907-9, while that in the drainage water and crops of the 

 gauges cropped with grass accounted only for 128*4 and 115*6 Ib. per 

 acre over the same period. The final rainfall before the account was 

 made up was so heavy as to deplete the gauges of nitrate, so that no 

 error arises through the retention of nitrate in the soil. 



Deherain's experiments made at Grignon, near Paris (82), between 

 1892 and 1897, also showed much more nitrate coming from the fallow 

 lysimeters than from those covered with crops even after allowing for 

 what was absorbed by the crop. In this case, however, it is uncertain 

 how much nitrate was left in the soil, the rainfall probably being in- 

 sufficient to wash it all out. 



Thus it seems to be an established fact that less nitrate accumu- 

 lates on cropped land than on fallow land, even after allowing for 

 what is absorbed by the crop. Although the actual experimental 

 figures refer only to the accumulation of nitrate we are probably justi- 

 fied in supposing that they indicate a diminished production of nitrate 

 in cropped land, otherwise we have to assume some destructive pro- 

 cess at work in the cropped soil that does not go on in the fallow soil, 

 an assumption for which there is no evidence at all. The wide range 

 of climatic conditions under which the result is obtained seems to pre- 

 clude any assumption that the diminished production is due to the 



