204 THE LIVING ORGANISMS OF THE SOIL [chap. 



had been removed ; this showed down to the depth of 

 9 inches an excess of nitrogen in the clover land, despite 

 the larger amount which had been removed in the crop. 



In Soil after Barley . 0-1416 per cent. Nitrogen. 



In Soil after Clover . 0-1566 >, 



In another experiment, land which had previously 

 grown beans and then been fallow for five years, was 

 sown with barley and clover in 1883, the clover being 

 allowed to stand in 1884 and 1885. At starting the 

 soil was analysed ; the surface 9 inches contained on 

 an average 2657 lbs. per acre of nitrogen, while of 

 nitrogen as nitric acid the soil only contained 24-7 lbs. 

 per acre down to a depth of 6 feet. As a result of the 

 three years' cropping with barley and clover, and then 

 with clover only, an average amount of 319-5 lbs. of 

 nitrogen was removed, yet the soil contained, on 

 analysis at the end of the experiment, 2832 lbs. of 

 nitrogen per acre in the top 9 inches, or a gain of 

 175 lbs. per acre in the three years, making a total, 

 with the crop removed, of nearly 500 lbs. of nitrogen 

 per acre to be accounted for. 



The consideration of field trials of this description 

 led many observers to think that there still might be 

 some fixation of free nitrogen, particularly by legumi- 

 nous plants. Voelcker, in England, when discussing 

 the power of a clover crop to accumulate nitrogen, 

 expressed the opinion that the atmosphere furnishes 

 nitrogenous food to that plant ; in France, it was 

 maintained by Ville ; Berthelot also brought evidence 

 to show that the soil itself, by the aid of its micro- 

 scopic vegetation, assimilated some free nitrogen. Even 

 in the laboratory experiments, some of Boussingault's 

 results, and others of Atwater, in America, showed a 

 gain of nitrogen. But the clearing up of the whole 



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