THE INFLUENCE OF PLANT RESIDUES ON NITRO- 

 GEN FIXATION AND ON LOSSES OF NITRATE 

 IN THE SOIL. 



By henry brougham HUTCHINSON. 

 {RolhamMed Experiwental Slalion.) 



(With Three Figures in text.) 



The incorporation of plant residues with the soil may give rise to a 

 number of different changes, any one of which tends to dominate the 

 rest according to the varying conditions of the general environment — 

 air and water supply, temperature, the reaction of the soil itself. Whilst, 

 under average conditions the easily decomposable constituents of the 

 plant are speedily resolved by the action of the soil flora, the more 

 resistant structures often persist unchanged for considerable periods, but 

 ultimately lose their identity and as humus become an integral part of 

 the soil. The generally accepted statement that organic matter possesses 

 value on account of its humus forming properties does not express fully 

 the influence of organic residues, and it is quite probable that the primary 

 and intermediate stages of decomposition are equally important from the 

 standpoint of soil fertility 



An indication of such effects of plant residues is afforded by two of the 

 Rothamsted plots which, since 1882 and 1885, have been allowed to revert 

 from arable to prairie conditions. As the result of analyses of the soil of 

 these plots, Hall (1) was able to show that during the twenty year period 

 of the observations very considerable accumulations of nitrogen had 

 taken place, and although it was recognised that the conditions were 

 complicated by the presence of leguminous plants in the herbage of one 

 of the plots, by the absorption of free ammonia from the atmosphere, 

 and the possible capillary uplift of nitrates from the permanent soil 

 water it was, at the same time, considered that part of these gains might 

 reasonably be ascribed to the activity of certain nitrogen fixing organisms 

 wliich have been found in these soils by Ashby(2). It was, in fact, con- 

 sidered that the carbohydrates formed by the decomposition of the crop 



