DISTRIBUTION OF MTK'IFVINC OIMIAMSMS -Jl 



tendency to increase and isl)ut litilr liiuhcr tliaii the jJiojMii-iinu 

 in the soil of other adjoinini]: meadows wliicli have oiiK lu-i-n 

 kid down to grass for tliirty years or so. Again, in tin- I'.id.td 

 balk wheat tield, tlie j)lot wliieli receives farniy.ird manure is 

 snppHed annnally with far more nitrogen than is renioNcd in 

 the crop. Dnring the earher years of the e\|)ciimcni> tlniv 

 was in consequence a rapid rise in the jiro|iortion ot niirogrn 

 in the soil, but this rise has diminished, and lias liecn latterly 

 by no means equal to the annual increment of nitrogen. A 

 state of equilibrium is eyentually attained, when the destructive 

 agencies find the conditions so fayourable for their develop- 

 ment that the quantity of nitrogen compounds broken down 

 to the state of gas becomes equal to the surplus of eonibine(l 

 nitrogen that is added year by year. 



III. — Nitrates in Cultivated Soils. 



The nitrifying organisms are in the main present only in the 

 surface soil which is subject to cultiyation ; at depths greater 

 than 9 inches from the smface the organisms become more 

 scanty and less effectiye in inducing nitrification in a suitable 

 medium. Dming the sampling of several of the Kothamsted 

 soils Warington took advantage of the pits dng into tiie 

 subsoil to obtain small samples of the undisturbed snbsoil. 

 portions of which were then introduced into solutions capable 

 of undergoing nitrification. It was found that the nitri 

 fying organisms were present in all the samples down to 

 o feet from the surface ; at 6 feet, where the snbsoil was clay, 

 half the samples failed to induce nitrification, at 8 feet the clay 

 subsoil showed no evidence of the presence of nitritying 

 organisms. Whenever the subsoil passe<l into the clialk loek. 

 which in one case extended to A\ithin .') leet of the sinlaci', nn 

 nitrifying organisms were found. Fractieally the whole of the 

 nitrification going on in a com})aratively close soil like that ol 

 Rothamsted takes place in the lirst U inches which gets 

 stirred about and ai^-rated by the action of the j)longh. 



It will now Ije reahsed that the most favomable condition.- 



