1907. | Nitrification in Acid Soils. 199, 
salts, contained 12°44 parts of nitric nitrogen per million of soil, whilst: 
the soil of Plot 9, which received 400 lb. of ammonium salts, contained 
617 parts nitric nitrogen per million, and that of the wnmanured Plot 3: 
contained only 1°78 parts. Such a relationship between the amount of 
nitrates in the soil and the amount of ammonia supplied to each plot 
indicates that the nitrates have been formed in the soil instead of being: 
derived from some extraneous source common to all the plots; this con- 
clusion is confirmed by the further behaviour of the soils during exposure, 
since in nearly all cases the nitrates were found to have increased. The. 
five weeks’ exposure was attended by an increase of nitrates in all the 
surface soils except in that of Plot 11-1, to which the largest amount of: 
ammonium salts is applied; similar, though smaller, increases were shown 
by all the other samples, except those taken from the depth of 113 to. 
135 cm., soil from which depth had not been observed to contain nitrifying 
organisms in the previous series of experiments. The two months’ exposure. 
(surface soils only) produced similar effects, the increase in nitrates being 
small in the soils from Plots 9 and 11-1. 
Although these results show that the nitrifying organisms cannot be 
wholly absent from the soil of the plots rendered acid by the use of 
ammonium salts, yet the quantity of nitrates produced during the exposure, 
favourable as were the conditions for nitrification, would not be sufficient 
to supply crops grown on these plots with the amount of nitrogen they 
usually remove from the land. During the five weeks’ period, the nitrates 
in the soil of Plot 9 increased by two parts per million ; in that of Plot 11-1 
by 0°64 part per million; assuming that these optimum rates were main- 
tained during a whole year, the total amount of nitrates produced would only 
amount to 50 lb. and 16 lb. respectively of nitrogen per acre. Yet, in 1904, 
Plot 9 produced 70:4 cwt. of hay, containing 94°6 Ib. of nitrogen, and 
Plot 11-1 98:2 ewt. of hay, containing 131 lb. of nitrogen, all of which 
must have been derived from the soil, as no leguminous plants are present. 
in the herbage. 
From these figures it is difficult to resist the conclusion that though 
nitrification may not be entirely suspended in these acid soils, it is so far- 
reduced that the plants cannot obtain in the form of nitrates all the nitrogen. 
they take up from the soil, but must draw the larger portion directly from 
the ammonium salts supplied as manure. Miintz* and Mazét have shown, 
that maize, another gramineous plant, can derive:its supply of nitrogen 
directly from ammonium salts, but attempts made by the authors to grow 
* “Comptes Rendus,’ 1889, vol. 109, p. 646. 
+ ‘Ann. de l’Inst. Pasteur,’ 1900, vol. 14, p. 26. 
