80 



EFFECT OF PHOSPHATES 



the untreated soil contain- -299 % of nitrogen and 11-80 % of organic 

 matter (loss on ignition). It seems far more probable, therefore, that 

 the result is mainly due to the direct effect of the phosphates on the 

 soil organisms bringing about nitrification. 



-2- 0j 



B 

 "-J 



-/23 



A-*-- '*"' 



8 / :--.S . : 



-4 : 



.* / 



,/\ 





/ 



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i -^ L* -A t 



29 

 March 



12 29 W 34 7 21 $ 19 2 / 30 t3 27 



April May June July Aucnst Sept. 



FIG. 17. Nitrate content of the Potted Soil from the Untreated Plot and the Basic 



Slag Plot, at Martin's Hearne. Soil Boulder clay. Season 1920. Soil from 

 Untreated Plot (3) Soil from Basic Slag Plot (2) . Rainfall 



28 



/ 



IS. 



19 3 17 31 /4- 28 12 Z6 9 Z3 6 30 27 

 April May June July August Sept. 



PIG. 18. Nitrate content of the Potted Soil from the Untreated and the Basic Slag 



Plots at Great Mulgraves, Horndon-on-the-Hill. Soil London clay. Season 1920. 



Soil from Untreated Plot Soil from Basic Slag Plot . 



The difference between the slag and untreated plots is striking, 

 and seems to indicate, in view of the fact that the Martin's Hearne 

 soil is sour, that on both these types of soil a deficiency in phosphates 

 is a more important factor in limiting nitrification than a deficiency 

 in lime. 



