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DIVISION S-1-SOIL PHYSICS

Portable, two-stage sampler for "difficult" soils

Applied Plant Sci., Dep. of Agriculture for Northern Ireland, Newforge Lane, Belfast, Northern Ireland BT9 5PX

	ABSTRACT

TOP ABSTRACT INTRODUCTION Materials and Methods Results and Discussion REFERENCES

 
A lightweight hand-sampler is described for taking uncompacted cores up to 1.5 m long and 49 by 49 mm in section. Cores were successfully taken from tilled gravelly brown earths or had intact unshattered earthworm tunnels even in samples with a high clay content. The sampler comprises two halves, two lengths of light, high quality angle-steel (2 m long x 50 mm wide). The two half-lengths are inserted separately into the soil. Tips are acutely pointed and sharpened with the chamfer to the outside. These cutting edges are constricted internally to give relief to the core. Steel caps are welded to the top of each half-length to receive hammer blows. The first half-length to be driven into the soil has a cube of hardwood fixed at the upper end and another is positioned just above the soil surface. These serve as alignment bearings for the second half-length. It is positioned tightly against the first half-length and driven until the steel caps just touch and overlap. The entire sampler and soil core are then withdrawn using a lever, the tip of which keys sequentially into a series of holes bored along the first half-length. A short steel tube attached horizontally across a piece of heavy marine-plywood provides a fulcrum for the lever.

	INTRODUCTION

TOP ABSTRACT INTRODUCTION Materials and Methods Results and Discussion REFERENCES

 
UNDISTURBED CORES OF SOIL are used for measuring bulk density, load bearing capacity, gas production on incubation, rooting depth, ease of water penetration, distribution of nutrients, fungi and soil animals, or to detect previous soil disturbance. Unfortunately if a tube-sampler is used to take a core, the longer this is the greater the likelihood of compression. Compaction builds up in front of the sampler as well as internally, increasing exponentially due to friction that causes the core to swell and grip the sampler walls ever more firmly. This note describes a simple, easily made sampler without these problems.

To be self-supporting during cutting, long cores usually have to be wide, while cores of convenient width (35–50 mm) are limited to 500-mm length (Ruark, 1985). Many undisturbed samples are usually somewhat compacted (Jamison et al., 1959). To alleviate this problem (Minotti et al., 1931) used a tube 600 mm in diam. and 2.7 m long. It only compacted the core at its circumference. This core was obtained in 4 h, using a 15000-lb-capacity forklift truck for driving and extraction. Kimmelshue et al. (1996) made use of a polyvinyl chloride (PVC) pipe 560 mm by 1.22 m long and Swallow et al. (1987) described an even wider steel tube sampler, hydraulically driven by machine. This had the advantages of a restriction at the cutting tip and a plastic liner.

As regards smaller diameter samplers, Smith and Lawson (1959) described a 50-mm-diam. hand-tool. This was a version of the King tube, modified by Veihmeyer (1929) and comprised a thin walled tube with a turned-in cutting edge to give relief. Cores were 300 mm long and were preferably taken from wet soil but without guarantee of freedom from compaction. Stewart (1943) described an ingenious but toxic variation of the King tube for sampling plastic soil (clay). The copper tip was dressed with mercury for lubrication.

In an effort to obtain undisturbed cores Coile (1936) placed an internal removable sleeve in a short relatively wide tube driven by hammering. Subsequently, various lined tube samplers were claimed to take undisturbed samples. These usually had plastic, brass, or aluminum inserts, sometimes split longitudinally. The best samplers had a slight constriction at the cutting edge to give relief. Long cores are often sequentially removed, usually in 300-mm lengths. At each stage the sampling hole may have to be reamed to give greater clearance. Tessier and Steppuhn (1990) claimed to have taken 1-m undisturbed cores using a mechanized sampler. Hendrickx et al. (1991) took 2-m cores for volumetric sampling using a motor-driven, high frequency, hammer-driven sampler. The latter had a wide cutting-ring to give both external and internal clearance. Hayden and Heinmann (1968) described a sampler with an outer tube having toothed, helical-flanges, allowing it plus its inner tube to be screwed into the soil. Cores were 300 by 75 mm. The design was similar to that of Powell (1936) or Andrews and Broadfoot (1958). The sampler described below contrasts with most of those above in its simplicity and lightness, taking undisturbed cores even from difficult soils.

	Materials and Methods

TOP ABSTRACT INTRODUCTION Materials and Methods Results and Discussion REFERENCES

 
The sampler is illustrated in Fig. 1 . Its essential feature is that it comprises two halves that are hammered into the soil separately. This avoids compressing the core. Two lengths of angle (2 m x 50 mm x 3-mm-thick spring steel) similar to those used in a bed frame, were used for construction. Each length had a cap of steel 20 mm deep welded across its top, to receive hammer blows. Figure 1 shows the back view of the second half-length to be driven and the front view of the first half-length, plus two cross-sections. In use the first half-length was driven into the soil leaving 500 mm or more protruding. A second guide block (not illustrated) was attached just above soil level. It had a lug to go through one of the holes in the first half-length plus an internal magnet to help retain it. The second half-length was pressed against these blocks and hammered into the soil until its cap just overlapped the cap of the first half-length.

View larger version (32K): [in this window] [in a new window]   Fig. 1 (a) Soil sampler, inserted as two halves: back view of the second half, front view of the second half, plus two sectional views. (b) Completed wire sampler with core and ready to be levered out. Note the cap of the second half here overlaps that of the first half

The lever used to extract the sampler was either a steel rod 1 m long by 23 mm in diameter with a narrow tip shaped as shown or a strong wooden baton with a narrow steel rod attached to and slightly protruding from one end. The fulcrum comprised a steel tube attached across a piece of plywood.

An initial test used an artificial soil profile built on a lightly compressed layer of soil 200 mm deep. Equal volumes of sieved brown earth were individually but lightly compressed into layers 40 mm thick and demarcated by bands of sawdust 2 mm thick. This was within a rigid container 600 mm in diameter. Cores were taken in three ways. In the method as described, or using the sampler halves joined together (with packing tape) to form a square tube, or using a 50-mm-diam. round tube. Six replicate samples were taken using each of the first two methods. The round tube sampler was abandoned when it was found impossible to sample more than three or four layers and these were equally difficult to force out of the tube. With the sampler used as a square tube the tape was removed to release the core.

	Results and Discussion

TOP ABSTRACT INTRODUCTION Materials and Methods Results and Discussion REFERENCES

 
In tests, samples were successfully taken from an artificial profile, from cultivated gravelly brown earth, from undisturbed brown earth over clay and from peat. The sampler with the halves separately driven, as described, did not measurably compress any of the horizons of the artificial profile despite the latter's delicate structure. The proof was that the core and the penetration depth were always within 10 mm of being identical in length. However, when the sampler halves were joined to make a tube only the first few horizons remained relatively uncompressed. Furthermore, it was only possible to sample nine of the 40-mm-thick layers. Those below this were compressed beneath the tube instead of being forced into it.

Because the layers in the test profile had been lightly firmed down by hand during its construction they were not of exactly the same thickness. Consequently the best comparison of the sampling methods was made as follows. The mean thickness of a layer after being taken with the sampler in tube form was expressed as a percentage of the same layer's mean thickness when taken by the sampler inserted as separate halves. This gave the following result, 100.1, 81.6, 68.3, 61.2, 61.8, 61.9, 64.8, 70.0, and 65.9%. This demonstrates that a tube sampler of this width starts to compress the core after penetrating only 40 mm and to fully compress it after 120 mm.

In field tests with the two-part sampler, cores were deemed uncompressed for the following reasons. A mark made on the outside of the sampler at soil level before extraction closely corresponded to the top of the core. Grass roots were dissected out undamaged, as were living earthworms, still within their tunnels.

Cores usually took several minutes to obtain. They were transported to base in plastic lined, wood boxes or in lengths of plastic guttering. Occasionally it was instructive to break samples lengthways, by levering the top half sideways. This gave a good view of horizons and soil structure, also producing a surface uncontaminated by smears or organisms from a higher level (useful in microbial sampling).

Peat samplers (designed by the author) but made in channel of relatively large section, incorporated devices to cut off the core at its base and also retain it against vacuum forces during extraction. These samplers employed the same principle as used above, with some versions successfully employed for over 30 years, particularly by the Northern Ireland Forest Service. These samplers have only recently been described, along with a recent design, a pointed, metal-tipped, plastic tube, cut longitudinally into halves (Seaby, 2000).

From the literature, including old and new catalogues, it is clear there are a wide range of soil samplers. Many are complex but cover most situations. The two-part sampler described above appears to use a novel principle of inserting the halves separately and was particularly light and easy to construct. A review of literature on peat samplers found three designs using the same principle, although none was sufficiently robust for soil sampling.

Received for publication January 15, 1999.

	REFERENCES

TOP ABSTRACT INTRODUCTION Materials and Methods Results and Discussion REFERENCES

 

• Andrews L.A., Broadfoot W.M. The San Dimas soil core sampler. Soil Sci. 1958;85:297-301.
• Coile T.S. Soil samplers. Soil Sci. 1936;42:139-142.
• Hayden C.W., Heinmann W.H., Jr. A hand-operated undisturbed core sampler. Soil Sci. 1968;106:153-156.
• Hendrickx J.M.H., Ritsema C.J., Boersma O.H., Dekker L.W., Hamminga W., van de Kolk J.W.H. Motor-driven portable soil core sampler for volumetric sampling. Soil Sci. Soc. Am. J. 1991;55:1792-1795.[Abstract/Free Full Text]
• Jamison V.C., Weaver H.A., Reed I.F. A hammer-driven soil core sampler. Soil Sci. 1959;69:487-496.
• Kimmelshue, J.E., R.O. Evans, J.W. Gilliam, C.R. Camp, E.J. Sadler, and R.E. Yoder. 1996. Extraction and instrumentation of round soil monoliths for monitoring evapotranspiration and solute movement. Evapotranspiration and irrigation scheduling. p. 1078–1087. In C.R. Camp (ed.) Proc. of the Int. Conf., San Antonio, TX. 3–6 Nov. 1996. ASAE Publ., St. Joseph, MI.
• Minotti P.L., Craig D., Jackson W.A. A rapid procedure for obtaining large, undisturbed soil cores. Soil Sci. Soc. Proc. 1931;29:218-221.
• Powell E.B. A new soil core sampler. Soil Sci. 1936;21:53-56.
• Ruark G.A. A refined soil coring system. Soil Sci. Soc. J. Am. 1985;49:278-281.[Abstract/Free Full Text]
• Seaby, D.A. 2000. Two designs for one-man, two-stage samplers for obtaining undisturbed cores of peat over 1m long. Forestry 74:(In press).
• Smith J.L., Lawson E.R. Sampler for gravelly plastic soils. Soil Sci. 1959;88:56-57.
• Stewart A.J. A soil tube for obtaining wet clay cores in an undisturbed structural condition. Soil Sci. 1943;55:247-251.
• Swallow C.W., Casual D.E., Owensby C.E. Soil coring machine for microplots and large cores. Agron. J. 1987;79:756-758.[Abstract/Free Full Text]
• Tessier S., Steppuhn H. Quick mount soil core sampler for measuring bulk density. Can. J. Soil Sci. 1990;70:115-118.
• Veihmeyer F.J. An improved soil sampling tube. Soil Sci. 1929;27:147-152.

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