vii.] NITRATES IN SOIL 223 



they effect, and by the mere mechanical distribution 

 of the bacteria into new quarters, where there are fresh 

 food supplies. In some experiments of Deherain's he 

 found that the drainage water from pots of cultivated 

 soil, which had been sent from a distance, and thus 

 much knocked about in travelling and filling into the 

 pot, contained as much as 466 to 664 parts of nitrogen 

 as nitric acid per million. The drainage water from the 

 Rothamsted wheat plots contains only from 10 to 20 

 parts per million ; even the cement tanks at Grignon, 

 2 metres cube, into which the soil had been filled, gave 

 drainage water containing only 39 parts of nitric 

 nitrogen per million. In another experiment a quantity 

 of soil was thrown upon a floor, and worked about 

 daily for six weeks ; on analysis it contained 0-05 1 

 per cent, of nitric nitrogen, as against -002 per cent, of 

 nitric nitrogen in the same soil left in situ. The diagram 

 (Fig. 15), due to King, shows the dependence of nitrate 

 production on temperature and the cultivation of the 

 soil. The lower curve shows the amount of nitrate 

 in parts per million in dry soil in the top foot of land, 

 which was not being cultivated because it carried clover 

 and oats. The upper curve shows the same results 

 obtained on well-tilled land carrying maize and potatoes. 

 On the cultivated land the proportion of nitrates rises 

 rapidly until the end of June, when the crop begins to 

 draw freely upon them, and reduces them to a minimum 

 throughout August and September. 



One of the best examples of the manner in which 

 the thorough working and aeration of a warm soil 

 promotes nitrification is seen in the management of 

 the turnip crop as usually grown in this country. 

 Though shallow-rooted, and taking away large quan- 

 tities of nitrogen per acre, it is usually grown with 

 but little nitrogenous manure ; phosphates with a little 



