224 



NITRIFICATION 



TABLE LXXVIII. Nitrogen as Nitrates in Broadbalk Wheat Soils, 

 October 1893. Lb. per acre. 



* To 72 inches only. 



It has already been pointed out that nitrification is practi- 

 cally confined to the surface soil, where only do the desirable 

 conditions prevail of numerous organisms, free aeration and 

 stirring of the soil, and nitrogenous matter easily attackable by 

 bacteria. This opinion is also borne out by the fact that the 

 drain-gauge with soil 60 inches deep yields practically the 

 same amount of nitrate as the shallower gauge where the soil 

 is only 20 inches deep. From this it follows that the nitrates 

 to be found in the lower depths of the subsoil are all derived 

 from the surface, and have been washed down with the rain. 



It will be noticed that in most cases shown in the table the 

 second 9 inches contains a larger amount of nitrates than the 

 surface soil, in some instances even the third 9 inches are richer 

 than the surface. This is merely due to the downward dis- 

 placement of the nitrates produced after the harvest by the 

 heavy rain which had fallen immediately before sampling. It 

 will also be noticed that in several cases there is a break in 

 continuity in the amount of nitrates between the third and fourth 

 depths. This is probably due to the tile drains, which lie at 

 about this depth and remove the drainage water charged with 



