146 Points in the Composition of Soils. 



covered with plates of glass, kept under proper conditions of 

 temperature and moisture for specified periods, extracted from 

 time to time, and the nitric nitrogen determined in the extracts. 



The periods were never less than twenty-eight days, and some- 

 times more. The rate of nitrification declined after the third and 

 fourth periods. There was a very marked increase in the rate 

 of nitrification in the subsoils during the eighth period compared 

 with the seventh, there having been ad Jed only as much as the 

 tenth of a gram of garden soil containing nitrifying organism. 



This result is of much interest, affording confirmation of the 

 view that the nitrogen of subsoils is subject to nitrification, if 

 only under suitable conditions, and that the growth of deep-rooted 

 plants may favour nitrification in the lower layers. 



Records show that the rich prairie sails of the Northwest 

 are competent to yield large crops ; but, under existing condi" 

 tions, they certainly do not on the average yield amounts at all 

 commensurate with their richness compared with the soils of 

 Great Britain, which have been under arable cultivation for 

 centuries. That the rich prairie soils do not yield more produce 

 than they do, is due partly to climate but largely to scarcity of 

 labour, and consequent imperfect cultivation, and to luxuriant 

 growth of weeds ; and until mixed agriculture, with stock feed- 

 ing, can be had recourse to, and local demand arises, the burn- 

 ing of the straw, and deficiency or waste of manure, are more 

 or less inevitable, but still exhaustiDg practices. So long as 

 land is cheap and labour dear some sacrifice of fertility is 

 unavoidable in the process of bringing these virgin soils under 

 profitable cultivation ; and the only remedy is to be found in the 

 increase of population. Still the fact should not be lost sight of, 

 that such practices of early settlement, however unavoidable, do 

 involve serious loss of fertility. 



A table has been prepared showing the comparative characters, 

 as to percentage of nitrogen and carbon, of exhausted arable 

 soils, of newly laid down pasture and of old pasture soils, at 

 Rothamsted, also of some other old arable soils in Great Britain ) 

 of some Illinois and Manitoba prairie soils ; and, lastly, of 

 some very rich Russian soils. A comparison of the figures leaves 

 no doubt that a rich virgin soil, or a permanent pasture surface 

 soil, is characterised by a relatively high percentage of nitrogen 



