Published online 27 October 2006
Published in Soil Sci Soc Am J 70:2161-2163 (2006)
DOI: 10.2136/sssaj2005.0312N
© 2006 Soil Science Society of America
677 S. Segoe Rd., Madison, WI 53711 USA
Nutrient Management & Soil & Plant Analysis-Note
A Soil Probe Pulling Device Facilitates Soil Sampling
John W. Wendt*
IITA, c/o Lambourn, Carolyn House, Croydon CR9 3EE, UK
* Corresponding author (j.wendt{at}cgiar.org)
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ABSTRACT
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Soil probes are hammered into the soil to sample uniform, undisturbed soil cores, and can also be used to dig uniform holes for permanent installation of devices to monitor soil moisture and soil solution composition. Extracting soil probes becomes increasingly difficult at increasing depths, particularly when the soil is dry, frozen, or has a cohesive consistency. The construction and operation of a device for extracting soil probes is described. The device can be constructed from inexpensive and universally available galvanized pipe and pipe joints, and a 25 mm width x 2 m length nylon strap. The device can be used to extract other soil sampling equipment that requires upward vertical force. A single person can generate over 1000 kg of upward force on the probe without excessive effort. Use of the probe does not strain the back, which is an important consideration as back injuries are a serious concern with manual soil probe extraction.
Abbreviations: NPT, National Pipe Thread • OD, outer diameter
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INTRODUCTION
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SOIL PROBES have numerous monitoring and experimental applications. A soil probe cuts a uniform, unmixed soil core from a given soil surface area. It is the most accurate tool for obtaining soil samples at desired depth increments, and can likewise be used to sample soils on a soil mass basis. Whereas an auger must be re-inserted for each depth increment sampled due to disturbance and mixing that can occur between different increments, a single soil probe core can be sectioned into several depth increments. This eliminates topsoil spilling into the hole and contaminating subsoil samples, which can occur with augers. Soil probes are also generally more easily driven into dry or frozen soils than augers, which encounter considerable resistance as they are twisted into the soil under such conditions. The hole left by a soil probe can be used to install moisture monitoring devices such as tensiometers, moisture blocks, and tubes for neutron probes and time domain reflectometry equipment. Narrow diameter, deep soil probes have applications in monitoring subsoil acidity and Al toxicity (Levy and Sumner, 1998), N dynamics (Hartemink et al., 2000), S supply (Menzies and Gillman, 1997), contaminant movement (Heberer et al., 1998), and assessing C stocks under different land use systems (Kotto-Same et al., 1997) in a relatively nondestructive manner.
One constraint to the use of soil probes is physically removing them from the ground once they have been driven in. Manually operated probes are driven into the soil using a slide hammer, which is attached to the probe using various coupling mechanisms that protect the probe from damage during hammering. The soil probe extracts a core slightly smaller than the outer probe diameter. The remaining soil is compacted against the outer probe wall as the probe is driven into the soil. This creates friction against the outer probe wall, which increases proportionately to the depth that the soil probe is driven. Dry or frozen soils, as well as moist soils with moderate to high clay contents, can generate considerable friction, particularly when the probe is driven to depths beyond 30 cm. Some soil probes such as JMC's Environmentalist subsoil probe (Clements Associates, Inc., Newton, IA), can sample at depths exceeding 6 m, and its removal facilitated by a foot jack. While usually effective, the foot jack is expensive, specific to the probe outer diameter (OD) of 28.6 mm, and cannot be used with probes of different diameters. Large diameter probes such as AMS's multi-stage core sampler (AMS Inc., American Falls, ID) can sample a 50-mm diameter core to depths up to 2 m, but are difficult to remove from many soils even at depths of 15 cm. Removal is done by pulling on a cross handle attached to the probe by a coupling mechanism. This can be extremely laborious and can result in back injury, becomes increasingly difficult as sampling depth increases, and is often physically impossible on cohesive soils. Another option is thrusting the slide hammer (attached to the probe with a coupling mechanism) upward, but this method is also slow, laborious, and not always successful on deep, dry, or cohesive soils. A further option is the use of hydraulic equipment to both drive and extract the probe. However, hydraulic equipment is very expensive relative to manual probes, and usually must be mounted to a tractor or truck (Schickedanz et al., 1973; Ginn et al., 1978; Swallow et al., 1987; Prior et al., 2004). This makes it inappropriate for many field and plot sampling applications where it may be impractical to position a tractor or truck. Prior and Rogers (1992) describe a portable coring system employing a pneumatic driver and an electric core extractor that can be used in areas not normally accessible by tractors, but which are still bulky and expensive relative to hand sampling equipment. Prior and Rogers (1994) describe a manually operated extractor constructed from a modified automotive ratchet jack, weighing some 11 kg, which is even less intrusive and is more suited to small plot, restricted areas.
We describe the construction and operation of a simple and inexpensive manual soil probe extracting device. The device is more lightweight (<4 kg) than that described by Prior and Rogers (1994), such that it can be carried to sampling sites without causing excessive fatigue. The materials employed are almost universally available. Construction requires no welds or special tools other than a pipe wrench. The device can be used to extract soil probes of various diameters and lengths without adapters.
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MATERIALS AND METHODS
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Construction
The soil probe pulling device is illustrated in Fig. 1
. The legs (Fig. 1A) are constructed from two pieces of 0.75 in. National Pipe Thread (NPT) standard galvanized pipe, which has an OD of approximately 27 mm, each 45 cm long, threaded at both ends. The leg supports are constructed from 4 pieces 0.75 in. NPT pipe (Fig. 1B) of 15 cm length, each threaded at one end, and are connected to the legs using two threaded galvanized T-joints (Fig. 1C) to accommodate the pipe. The two legs are joined at the top using a pivot rod composed of a single 20-cm section of 0.75 in. galvanized pipe threaded at both ends (Fig. 1D), connected to the legs with two threaded L-joints (Fig. 1E). A T-joint, (Fig. 1F) threaded to accommodate 1 in. NPT pipe at the two ends and the 0.75 in. NPT pipe at the center, is slid over part 1D, and pivots freely around this piece. The handle (Fig. 1G), composed of a single piece of 0.75 in. NPT galvanized pipe piece of 45 cm length and treaded on one end, is connected to the T-joint 1F at the threaded end. All threaded connections are first wrapped with Teflon thread tape (Dupont, Wilmington, DE) to facilitate the connection and to prevent corrosion at the threaded joints.
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Fig. 1. Parts used in the construction of the soil probe puller. A. Legs (2): 0.75 in. NPT pipe, 18 in. (45 cm) long, threaded both ends. B. Leg supports (4): 0.75 in. NPT pipe, 6'' (15 cm) long; threaded one end. C. T-joints (2), 0.75 in. NPT. D. Pivot rod (1), 0.75 in. NPT pipe, 8 in. (20 cm) long, threaded both ends. E. L-joints (2), 0.75 in. NPT. F. T joint, 1 in. NPT (ends) x 0.75 in. NPT (center). G. Handle, 0.75 in. NPT pipe, 18 in. (45 cm) long, threaded one end.
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Galvanized pipe can vary greatly in quality. Low quality, thin-walled pipe can fail under operation, particularly at the treaded ends of the pivot rod (Fig. 1D) and the threaded ends of the legs (Fig. 1B). It is important to choose galvanized pipe that has a minimum wall thickness of 3 mm.
Operation
A nylon strap of 2 m length and 25 mm width and approximately 2 mm thickness is used to connect the soil probe puller to the soil probe. This nylon strap described has a rated tensile strength of 1700 kg. The strap is doubled, then attached to the probe cross handle using a Lark's head knot (Fig. 2A
). The illustrated knot will not tighten under tension and is therefore easily released from the device. Knots that tighten under tension becomes extremely difficult if not impossible to untie. If a cross handle is not available, the strap can be directly connected to the probe body using the same knot (Fig. 2B), which will catch on the head of the soil probe under tension.
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Fig. 2. Attaching the nylon strap to the probe cross handle (A) using a Lark's head knot, and (B) directly to a probe, also using a Lark's head knot.
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The soil probe puller is then positioned above the probe, and the doubled strap is wrapped around the probe handle as in Fig. 3A
. It is vital that the single wrap is done to the underside of the handle as illustrated, rather than over-wrapped as in Fig. 3B. The under-wrap will grip the strap as the handle is pivoted. If the strap is over-wrapped, the strap will slip as the handle is pivoted. Once the strap has been wrapped around the handle, the probe puller is re-positioned such that the direction of the strap is directly aligned over the probe as in Fig. 4
. This permits the force generated by the probe puller to pull directly up on the probe. If not directly aligned above the probe, the soil puller will slightly torque the probe and can reduce the vertical force on the probe required for extraction while increasing frictional forces on the outer probe walls.
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Fig. 4. Extraction of the probe using a nylon strap (Fig. 4A) and with a chain (Fig. 4B) for deep soil samplers. Slight pressure with the thumb will assure that the chain grips the probe anywhere along the probe body.
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Once the probe puller is properly positioned, the handle is extended vertically and the strap pulled snugly with one hand, while the other hand is used to pivot the handle downward (Fig. 4A). This will apply tension on the strap and lift the probe. The handle is then re-extended vertically, the strap pulled snugly, and the process repeated until the probe has been extracted.
For extremely long probes used for deep soil sampling, or probes that do not have handles at the top to attach the nylon strap, it is necessary to grip the smooth probe body for extraction. This cannot be accomplished with a nylon strap, as the strap will slip. In this case, a chain can be used in place of the strap as in Fig. 4B. The same Lark's head knot as is illustrated with the strap in Fig. 3B is used but with a chain, and pulled snugly around the probe body. Only one end of the chain need be under-wrapped to the handle. The chain will grip the probe body when the handle is pivoted. A small amount of pressure applied by hand where the chain grips the probe will ensure a snug grip. When the handle is pivoted downward, the probe will elevate 5 to 10 cm. When the handle is moved vertically again, the chain knot will fall; a small amount of force applied with the other hand will resecure the chain to the probe body, and the process is repeated. Small-link chains (each link no more than 30 mm) are most desirable, and should be sufficiently strong to support 2000 kg of tension.
The mechanical advantage generated by the device is approximately 20:1, meaning that 50 kg of downward pressure on the handle will generate 1000 kg of upward lift. Applying 50 kg of downward force is simply a matter of placing one's body weight over the end of the handle and leaning downward onto the handle. This effectively uses the body weight to leverage an upward force. We have found that a 6-cm OD probe hammered to 60 cm in cohesive soils that cannot be budged by two able bodied persons pulling together on either side of the handle can be extracted by a single person using the soil puller in less than a minute.
The soil probe pulling device as illustrated costs less than $15 in terms of materials. Due to its small size and weight, it does not require disassembly for transport to the sampling area.
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ACKNOWLEDGMENTS
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Core funding from the International Institute for Tropical Agriculture was used to develop and test the soil probe pulling device.
Received for publication September 21, 2005.
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REFERENCES
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- Ginn, L.H., L.G. Heatherly, and W.J. Russell. 1978. Assembly for mounting hydraulic soil core sampler on tractor front. Agron. J. 70:512–514.[Abstract/Free Full Text]
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- Levy, G.J., and M.E. Sumner. 1998. Mined and by-product gypsum as soil amendments and conditioners. p. 197–215. In A. Wallace and R.E. Terry (ed.) Handbook of soil conditioners: Substances that enhance the physical properties of soil. Marcel Dekker Inc.; New York.
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- Prior, S.A., and H.H. Rogers. 1992. A portable soil coring system that minimizes plot disturbance. Agron. J. 84:1073–1077.[Abstract/Free Full Text]
- Prior, S.A., and H.H. Rogers. 1994. A manual soil coring system for soil-root studies. Commun. Soil Sci. Plant Anal. 25:517–522.
- Prior, S.A., G.B. Runion, H.A. Torbert, and D.C. Erbach. 2004. A hydraulic coring system for soil-root studies. Agron. J. 96:1202–1205.[Abstract/Free Full Text]
- Schickedanz, D.M., A.B. Onken, T. Cummings, and R.M. Jones. 1973. A tractor-mounted hydraulically-operated soil sampler for rapid soil coring. Agron. J. 65:339–340.[Abstract/Free Full Text]
- Swallow, C.W., D.E. Kissel, and C.E. Owensby. 1987. Soil coring machine for microplots and large soil cores. Agron. J. 79:756–758.[Abstract/Free Full Text]
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ABSTRACT
INTRODUCTION
