6 Podsol

Podzolic soils are those with a peaty surface layer with humus and/or iron-enriched subsoils.   They form in well-drained materials, usually acidic with few nutrients especially where the rainfall is high or the vegetation is dominated by heather or conifers.  The bark and needles of conifers, together with the surface litter, release organic compounds (chelates, tannins and polyphenols) which help to make metals (iron, aluminium, manganese) soluble and mobile in the soil.  There are two main soil groups, brown podzolic and podzol.

In the brown podzolic soil, the metals are ‘mobile’ and the iron gives a bright orange colour to the subsoil (Bs horizon) but there is no vertical movement.  In the podzol there is clear evidence of downward movement to leave a greyish, leached E horizon and forming either an enriched Bs horizon or an ironpan where there is sufficient enrichment of aluminium and iron to cement the soil material into a hard, impenetrable layer.   The ironpan can restrict water movement leading to waterlogging in the profile above and thus develop a soil which is intermediate between podzol and gley.

Location:  Bodafon, Anglesey SH471852.  Iron Podzol  (Bodafon Series). Turn left off the A5025 at Bryn Refail and follow the minor road for about a mile onto Bodafon Mountain.  Turn right onto a track to Clegir Farm and park in the parking area.  The soil profile is exposed in the quarry immediately in front of you, but access may be easier from the road.   The soil is developed in post-glacial scree from the Precambrian quartzite forming the mountain.

Profile  (NB extremely variable along the exposure)

0-10       O           black peat, abundant roots, clear boundary

10-45    E            dark grey, sandy loam, very stony, clear irregular boundary

45-55    Bh          very dark brown humus-stained stony sandy loam, irregular boundary to

55-95    Bs          orange-brown extremely stony layer, irregular boundary

95 – 150+            CR   white-weathering scree material (quartzite)

Not usually visible beneath the profile is  reddish-brown till material similar to the parent material of the Salop and Flint series profiles visible elsewhere on Anglesey.

A similar soil can be seen near South Stack in a small quarry behind the public toilets (SH210820), again formed in post-glacial scree from the Precambrian quartzite of Holyhead Mountain.

Location: Denbigh Moors, Clwyd – leave the A5 at Pentrefoelas on the A543 towards Denbigh, then turn northwards along a minor road signposted to Llyn Aled. Continue on for about 1.5km then park by Aled Isaf  Reservoir (SH915597) and examine the soil anywhere along the roadside.   The soil varies considerably and the photograph below is a composite of two variations.   (Wilcocks Series Stagnohumic gley and Crowdy Series peat are passed on the way to this site.)

Ironpan stagnopodzol  (Hiraethog Series).  Parent material is till derived largely from local Silurian shales.   Moorland vegetation heather (Calluna), bilberry (Vaccinium), rushes (Juncus) and grasses, Deschampsia and Nardus spp.),  land use – rough grazing.

 

Profile

0-24      O           black peat, stoneless, many fine roots, abrupt, wavy boundary

24-33    Eag        light brownish-grey silty clay loam with few distinct mottles and streaks of organic matter in cracks.  Massive structure, few roots, sharp irregular boundary.

33-34    Bf          thin ironpan with black top and reddish base, continuous, weakly cemented.  Root mat on top.

34-60    Bs          bright orange-brown, silty clay loam, unmottled, moderately stony, massive structure. Thin, discontinuous ironpan in middle of horizon.  clear irregular boundary.

60-80+  BC          yellowish-brown sandy silt loam, moderately stony, mainly shale fragments in finer matrix.