Plant and Soil 51,297 300 (1979) Ms. 3537

A C O R E R F O R T A K I N G U N D I S T U R B E D P E A T S A M P L E S

by S. P. CUTTLE and D. C. MALCOLM

Department of Forestry and Natural Resources, University of Edinburgh, King's Buildings, Edinburgh EH9 3JU, Scotland, U.K.

Key words

Corer Peat Undisturbed samples

Summary

A corer is described for sampling peats to a depth of 1 m with minimum disturbance of the sample. The instrument is simple and inexpensive to construct and is suitable for routine sampling operations.

Introduction

Core samples are frequently taken from soil profiles for the determination of physical characteristics such as bulk density and to examine the vertical distribution of roots or nutrients. Many designs of corer are in use but all aim to remove an 'undisturbed' core with minimal compact ion due to the driving of the corer. It is well known that a satisfactory design of corer depends on the relationship between its wall thickness and the cross-sectional area I .

In peat soils special problems in sampling arise due to the plastic nature of the material and its high water content. These factors readily allow deformation of the core and impede its intact removal due to the suction developed. It is particularly important to obtain accurate estimates of bulk density in these soils to express concentrations of mineral elements on a volume basis.

C o m m o n methods of sampling peat use the Hiller pattern of sampler, which destroys the physical structure of the sample, but can sample to considerable depths. An improved design described by Jowsey 2 requires the rotation of a sample chamber in situ which may result in some sample deformation. An alternative approach is to drive a core sampler to the required depth and then excavate around it to provide an 'undisturbed' monolith. This procedure retains the sample structure but destroys the sampling site and is unsuitable for use in,extant nutrition experiments.

This note describes the design of a peat corer that avoids these problems and provides an 'undisturbed' core of known dimensions up to 1 metre in length; a depth usually adequate for plant nutrit ional studies.

298 SHORT COMMUNICATION

Desist~1 (l/l(/ co/ lslr t tct io/t

The main part of the corer is constructed from metal box trunking as used to encase electrical wiring. The material is obtainable in various sizes and is manufactured from sheet steel in two pieces; one of three equal sides with narrow inturned flanges to add strength and support for the other piece which forms an overlapping lid. The trunking used in this design was of 50 mm side and 1 mm wall thickness giving a cross sectional area of 25 cm 2. The length adopted was 1.4m.

Details of the design and construction are given in Figure 1. The insertion and driving of the corer is improved by sloping the lower ends of the sides and sharpening their outer edges to give a slicing action through the peat. To permit easy access to the core the flanges along the inner faces of the side walls are removed except for the lowermost 20 mm which are retained to provide directional control on inserting the corer into the peat. The uppermost 150rnm of flange is also retained to give additional support to the steel head made from two short lengths of steel angle welded together and capped with a square of similar material. The head fits tightly into the trunking without deforming it, making a rigid mounting for the handle and a surface for driving the corer with a hammer if this proves necessary.

j Lugs

.A Main handle

\ I

SECTION AA

T-hcndte

~ Collar Lid Spacers

Main / ~Stee[ head N body

Position of side flanges on main body

S C A L E

0 5 0 t u r n , , , , , ,

Fig. 1. Details of the corer design.

SHORT COMMUNICATION 299

A collar of bent sheet steel is mounted over the open face of the corer, with spacing pieces, to retain the box lid in close contact with the edges of the main section while allowing it to slide freely. The steel head, collar and spacing pieces are fixed in position by pop rivets through the sides and back of the corer. A handle of steel tube (25 mm o.d.) is inserted through a hole drilled laterally through the head of the corer and retained in position with clips on both sides. The removable box lid has its lower end pointed and sharpened with the tip slightly angled towards the core to ensure it remains in contact with the box section while being inserted. At its upper end two lugs, formed by bending out short sections of the lid sides, locate on the collar at full insertion. These ensure that both parts are raised together when the corer is removed from the peat. Insertion and removal of the box lid from the main body is aided by a T-shaped handle attached to its upper end.

Operation

After removal of surface vegetation from the sampling location, the main section of the corer is pressed vertically into the peat to the required depth. The box lid is then passed through the collar and driven in to its stop position. Core deformation is avoided as the first cut prepares three sides of the core, the fourth continuing to support the peat column. When this is severed by the second cut the sample is retained firmly by the skin friction of the box section.

The corer and sample are removed by lifting vertically; if necessary two persons can lift by passing a steel rod through the tube handle. In wet peats the suction forces produced on removal of the corer can be reduced by inserting a tube, either separately or attached to the box lid, to admit air at the base of the sample as it is withdrawn. The sample is held in place by friction and.normally breaks offwithin 0.1 m from the bottom end of the corer so that a core of 1 m may be obtained by inserting the corer to 1.1 m. Where marked discontinuities occur within the peat at depths greater than about 0.6 m, cores may break leaving the lower portion of the sample in the ground.

Extracted from the peat the box lid is removed and the core exposed. After cutting off the lower torn portion, the sample may be removed as a single piece or cut into sections for separate treatment.

Conclusion

The corer described was designed for sampling in existing nutritional experiments in young tree plantations formed on drained deep peats and has proved suitable for use on a variety of peat types. The slicing action of the cutting edges enables it to pass through small roots and partially dried peats. As it is simple to use and can be readily cleaned between samples the corer is a useful tool for routine sampling where samples of known volume and depth are required. The materials used in its construction are cheap and easily obtained so that several models of different size may be constructed to suit particular sampling needs.

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Acknowledqements

We are grateful to D. Mackenzie for his assistance in the construction of the corer and to 1. Stenhouse for the preparation of the figure.

Received 20 July 1977

ReJerences

Baver, L. D. 1956 Soil Physics, John Wiley and Sons, Inc., New York. Jowsey, P. C. 1966 New Phytologist 65, 245 248.