The Soil Complex in Relation to Plant Communities: III. Moorlands and Bogs

Abstract

WHILE the preceding paper of this series dealt with woodland soils, this one describes in a similar manner some typical moorland soils, the primary basis of classification being the vegetation types occurring on them. The methods employed were described fully in the first paper of the series (1938). They determine the pH value from the potential at a bright platinum electrode in a quinhydrone saturated soil suspension, the determination being subject to the usual routine checks. Comber's thiocyanate test as modified by Misra is used to detect both base deficiency and the presence of replaceable ferrous iron. In the tables a single figure shows the depth of the colour with thiocyanate (scale 0-4). When a deepening of this colour is produced on adding hydrogen peroxide (one drop), the second colour is shown as a second figure, e.g. 2/3. The presence of nitrates in the fresh soil is detected by the production (in a clear aqueous extract) of a blue colour with diphenylamine. As nitrates are almost invariably absent in the soils described in this paper, only their presence is noted in the tables. The electrical potential of the soil is recorded in the tables as E5, that is, the potential (Eh) in millivolts (mY.) corrected to pH 5 on the assumption that each unit increase of pH causes a decrease of Eh of 58 mV. The electrical potential thus measured is assumed to be an oxidation-reduction potential for reasons given in the first paper of the series. Further, because ferrous iron is usually present and nitrates are apparently not formed below an E5 of 320 mY. soils of potential below this level are called reducing while those above E5 350 mV. are termed oxidizing. The latter contain no replaceable ferrous iron according to the test used. These previous conclusions are further exemplified by the data given in this paper. The method of sampling chiefly used in this work has been to transport fresh samples of soil rapidly to the laboratory with as little disturbance of texture, aeration or temperature as is possible. As indicated in an earlier discussion, the toluol method of sterilizing is often less satisfactory with damp soils and hence has been used sparingly in the present series. A few results are also given for field determinations. Generally speaking, the aim has been to carry out the observations on unaltered soils. Normally the samples have been collected from a nominal depth of 10 cm. below the soil surface. On account of the irregularity of the surfaces, this depth must be approximate. Finally, the figures given represent late summer conditions (August and September). Almost all the soils described in this paper, with a few exceptions which are