1907. | Nitrification in Acid Soils. 203 
nitrification, though considerably reduced, does go on in the same soil under 
field conditions. The explanation is probably to be found in the want of 
uniformity in a solid material like soil; though the soil of Plot 11-1 is on 
the whole so acid, the analyses show that it still contains 0°16 per cent. of 
finely divided caicium carbonate, each of the grains of which would be 
a centre for nitrification, though the process might not be going on outside 
the region kept neutral by the calcium carbonate. Further, all chemical 
actions in a soil must be much modified and localised by having to take 
place in the thin film of water clinging by surface tension to the soil 
particles; diffusion would be very slow, so that interactions of a quite 
opposite nature might be taking place at the same time and within a very 
short distance. 
This nitrification in acid soils is not unlike the case investigated by Chick,* 
who found that sewage nitrifies freely in passing through a coke bed, though 
the amount of organic matter dissolved in the sewage either entering 
or leaving the filter bed is sufficient to inhibit the nitrification of the liquid 
an vitro. 
The authors conclude, then, that nitrification will continue in the 
Rothamsted soils as long as any particles of available calcium carbonate 
remain disseminated through them; the continuance of the present manurial 
treatment, however, must eventually reduce the soil to a uniformly acid 
condition, when nitrification may be expected to cease, just as happens in the 
case of peat or other naturally acid soils. The unhealthy condition of the 
plots may be set down to the fact that their acidity checks the work of the 
nitrifying and other bacteria and promotes instead the development of moulds. 
The moulds must compete with the grass for the nitrogen compounds supplied 
as manure, but whether they injure the crop in other ways is under further 
investigation. 
EXPERIMENTAL. 
A. Sow and Manure. 
The following table shows the manurial treatment of the plots in question 
every year since 1856, together with the average yield of hay per acre and 
the nitrogen removed therein. | 
Ammonium Ammonium  Super- Potassium Sodium Magnesium Average Nitrogen 
Plot. sulphate. chloride. phosphate. sulphate. sulphate. sulphate. yield of hay. per acre. 
lb. lb. ’ ewt. lb. Ib. lb. ewt. Ib. 
3 — — — = = — 21 °6 33 °9 
4-2 200 200 3°5 — — ; — 35 °7 -66 1 
9 200 200 3°5 500 100 100 54 °4 76 °8 
1i-1 | 300 300 3°5 500 100 100 66 °8 107 ‘2 
* ‘Roy. Soc. Proc.,’ 1906, B, vol. 77, p. 241. 
VOL. LXXX.—B. R 
