ae Nitrification in Acid Sorls. » 211 
found with the Mucor; at the same time, ammoniacal nitrogen has been 
withdrawn from solution in amounts accounting for rather more than half 
of the observed acidity. 
- Another set of observations made by Dr. H. B. Hutchinson gave the 
following results :— 
Acidity produced and ammonia withdrawn from solution containing 1 per 
cent. dextrose and 0°2 per cent. ammonium sulphate, during 21 days’ growth 
of various moulds isolated from Plot 11-1. 
Cubic centimetres of Tenth Normal Acid per 100 c.c. Culture Medium. 
Acid equivalent of 
Organism. Acidity. ammonia withdrawn. 
ICON SPs 2 (25: gu0es coo aue 6-0 hb “E 
Mucor be Fake: eee 41 5 °6 
MCI COP EL revs kaise eolaaenes 5 *44 9°6 
(Penicillin sa. .css-s3.denne i 5 12 °4 
Acrostalagmus ............ 10°1 11°9 
Trichoderma I ............ 11°3 13 °9 
Trichoderma II ......... 12 °54 13 °6 
In these cases there was always a greater amount of ammonia withdrawn 
from solution than was equivalent to the acidity measured, which, as 
before, amounts to a concentration of from 7/200 to n/70 in the final 
solution. It is further significant that the degree of acidity developed in 
the culture solutions is of about the same order, between fiftieth and two- 
hundredth normal, as that which was found to exist in the soil water of the 
field plots. 
Summary. 
In the soil of certain of the permanent grass plots at Rothamsted, which 
is distinctly acid in consequence of the long-continued use of ammonium 
chloride and sulphate as manure, nitrification is greatly reduced, and the 
nitrifying bacteria are only found sparingly. In bulk, nitrification still goes 
on slowly, despite the acidity of the soil. Water extracts of the soil will not 
permit of nitrification unless they are previously neutralised. The amount of 
nitrate produced would not be sufficient for the nitrogen taken up by the 
crop, which must, in the main, utilise the ammonium salts without previous 
change. The acidity is chiefly due to sparingly soluble “humic” acids; free 
hydrochloric and sulphuric acids are also present, because the soil extract 
contains soluble acid in quantities comparable to the amount of chlorides 
and sulphates also present, and to the ammonium sulphate and chloride 
annually supplied as manure. 
The acidity is not brought about by purely chemical or physical actions 
of the soil upon the ammonium salts, but by various micro-fungi which are 
able to remove ammonia from a solution of its salts and set free the acids 
