THE INFLUENCE OF EARTHWORMS ON SOIL REACTION. 415 
The Influence of Earthworms on Soil Reaction and the Stratification of 
Undisturbed Soils. By E. J. SarisBury, D.Sc., F.L.S. (Reader in 
Ecology, University of London, University College). 
(With 3 Text-figures.) 
[Read 15th November, 1923.] 
To appreciate the significance of Earthworm action on the acidity of undis- 
turbed soils, it is essential to recognize the marked gradient with respect to 
hydrogen-ion concentration which such soils exhibit. The author has already 
shown that just as there is a fairly rapid increase in the organic content of 
the soil when we pass from the subsoil to the surface, so too there is usually 
a marked rise in the real acidity in the same direction (cf. Salisbury, E. J., 
* Stratification and Hydrogen-ion Concentration of the Soil in relation to 
Leaching and Plant-succession, with special reference to Woodlands," Journal 
of Ecology, vol. ix. pp. 220-240, 1922; ef. also Discussion on Soil Problems, 
Trans. Faraday Society, 1921). The following data for various types of 
plant community illustrate this gradient of reaction and organic content in 
undisturbed soils :— 
TABLE I. 
- Organie Content and pH at Varying Depths. 
(Organie= Loss on ignition corrected for CO, evolved from earbonates.) 
| | | | " - 
. Depth | Oak Wood. Beech Wood. Chalk Down. Pine W ood 
in inches. | (nr. Wimborne). 
0-2 Org- 17°5°/, pH 54) Org- 13:0°/, pH 6-2 360 ‘Jo pH 7-4 Org- 74°/, pH 45 
| &nic. anic. anic. 
2-4 »  98'pH55| „ 90° pH60| 235° pH75 | „ 74°/, pH 45 
4-6 | ,  T2",pH56, „ 88°, pll64 235°/, pH76 | „ 15% pH 45 
6-9 
61%, pH56 , 90%,pHr2 pHT6| „ 62°, pH50 
| 
| 
| 
l 
Evidence has been adduced elsewhere to show that for a given mineral 
substratum and with a uniform vegetation there is, up to a point determined 
by the origin of the organic material, an increase of acidity accompanying 
increase in the organic content of the soil (cf. Salisbury, Zoe. cit., and 
Salisbury, E. J., “The Soils of Blakeney Point: A Study in Edaphie Suc- 
cession,” Ann. Bot. vol. xxxvi. pp. 391-432, 1922). This, however, only 
holds where the conditions are approximately uniform, since the rate of decay 
influenees reaction by reason of the earlier stages being more acid than the 
later stages of decomposition. 
LINN. JOURN.—BOTANY, VOL. XLVI. 21 
