ON ACCUMULATION OF NITRATES 



79 



not removed and potted till April 19th, the first nitrate determination 

 being made sixteen days afterwards on May 5th. 



The nitrate contents of the potted soils as determined at various 

 dates throughout the season are given in Table XLIII. 



TABLE XLIII. ACCUMULATION OF NITRATE IN THE POTTED SOILS 

 FROM MARTIN'S HEARNE AND HORNDON-ON-THE-HILL 



Nitrate nitrogen parts per million of dry soil 



The general trend of the figures for both centres is very similar. 

 There is a rapid accumulation of nitrate on the slag plots during the 

 period May 19th to July 2nd. The results are illustrated in Figs. 17 

 and 18. The curves indicate a much greater and a much more 

 rapid accumulation of nitrate in the soil from the slag plots than in 

 the soil from the corresponding untreated plots. This can only be due 

 to one or both of two causes: 



1. The nitrification of the nitrogenous matter accumulated in the 

 slag plots by the nodule organisms. 



2. The direct effect of the slag on the soil organisms which bring 

 about nitrification. 



It is difficult to understand how the addition of a comparatively 

 small amount of nitrogenous organic matter to the already big accu- 

 mulation in the experimental soils can be responsible for such a 

 difference. Particularly is this the case at Martin's Hearne where 



