Hydraulically powered soil core sampler and its application to soil density and porosity estimation

Transcription

1 Soil & Tillage Research 52 (1999) 113±120 Hydraulically powered soil core sampler and its application to soil density and porosity estimation Nidal H. Abu-Hamdeh *, Hamid F. Al-Jalil Jordan University of Science and Technology, Agricultural Engineering and Technology Dept., PO Box 3030, Irbid, Jordan Received 5 February 1999; received in revised form 8 June 1999; accepted 24 June 1999 Abstract The design of a hydraulically powered soil core sampler used to collect undisturbed soil samples at different depths in the eld is presented. The hydraulic actuation of the coring probe reduces the physical effort and time required by the operators. The device is constructed from a three-point hitch frame equipped with a gearbox, retractable legs, hydraulic cylinder and probe. The legs are driven from the tractor power takeoff shaft through a gearbox that can change the direction of rotation of worm gear shaft. The worm gears drive power screws that extend the legs to hold part of the tractor weight. The tractor auxiliary hydraulic power actuates the cylinder to push the probe into the soil. The device was tested in the eld successively to collect soil samples for physical properties measurements. The results from the eld compaction study of the hydraulically powered soil core sampler con rmed that the system could rapidly collect soil cores for measuring soil properties. Changes in soil physical properties caused by a KUBOTA M8030 tractor with 18.4 R30 tires at 100 kpa with a loaded 1500 kg seed drill mounted on the tractor were measured for soil samples obtained by the soil core sampler and by the manual sampling method. The bulk density and total porosity data from this eld experiment showed that signi cant effects were present down to a depth of 50 cm. In addition, the results obtained using the soil core sampler were close to those obtained by the manual sampling method. # 1999 Elsevier Science B.V. All rights reserved. Keywords: Soil core sampler; Hydraulic actuation; Compaction; Bulk density; Total porosity 1. Introduction Precise and rapid in-situ characterization of soil physical properties is a major constraint toward development and adoption of sustainable systems of soil surface management. Presently, the measurement of most soil physical properties is a time-consuming process. For this reason, much soil related studies * Corresponding author. Tel.: ; fax: address: nidal@just.edu.jo (N.H. Abu-Hamdeh) focus on changes in only one property such as bulk density, cone index or saturated hydraulic conductivity. A review by Soane and Pidgeon (1981) indicates the need to collect data as rapidly as possible to avoid variations in soil properties due to weather changes. Collection of data within the period of 1 or 2 days is suggested. Farmers and agricultural researchers around the world are concerned about soil compaction. Compaction of soils is seldom measured directly. The usual procedure is to determine the change in a parameter or /99/$ ± see front matter # 1999 Elsevier Science B.V. All rights reserved. PII: S (99)

2 114 N.H. Abu-Hamdeh, H.F. Al-Jalil / Soil & Tillage Research 52 (1999) 113±120 set of parameters as a consequence of a compacting force. Compaction of agricultural soils results in increased soil bulk density (Mckibben, 1971; Wells and Burt, 1984; Ngunjiri and Siemens, 1993), and decreased porosity (Wood et al., 1993), hydraulic conductivity (Gupta et al., 1990; Wood et al., 1993) and air permeability (Freitag, 1971; Kunnemann and Wittmuss, 1976). In fact, most of the research uses the measurement of such properties for the evaluation of soil compaction. The compaction process is not well understood. The lack of understanding is closely related to the de ciency in instrumentation and techniques for measuring soil compaction. Many of compaction symptoms are related to changes in the soil's physical properties. Soil bulk density is one of the most frequently used measures of compaction. Bulk density is found by determining the weight of dry soil sample that occupies a core of known volume. The core sampling method usually determines bulk density. In this method, an open ended metal cylinder is either pressed or hammered into the soil. The cylinder is then excavated and weighted together with the soil core after the latter has been trimmed ush with the end of the cylinder. As the volume of the cylinder is known, the bulk density can be calculated by dividing the oven-dry weight of the core by its volume. Presently, the measurement of most soil physical properties is a time consuming process. Compounding the problem of quantifying the properties is the large variations among soil samples and the disturbance of these samples. This indicates the need of a portable system to measure soil physical properties rapidly, accurately, and with a minimal operator effort. Morgan et al. (1993) describe a soil test vehicle on which instruments could be mounted for the measurement of bulk density, porosity, air permeability, and cone penetration resistance. Fig. 1. Photograph of the hydraulically powered soil core sampler mounted on a tractor. data obtained will be useful for the study of tillage effects and soil compaction on soil physical properties. Also, the data will be important to civil engineers in the construction eld. A main bene t of the system is that it is expected to sample ten core samples down to a depth of 50 cm within about 10 min or less. 2. Objectives The purpose of this project was to design a hydraulically powered soil core sampler (HPSCS) used to collect soil samples at different depths in the eld (Fig. 1). The soil samples will be used to measure physical properties (density, porosity, and permeability, strength, moisture content, etc.) of soil cores. The 3. Materials and methods 3.1. Design and operation of the soil core sampler The purpose of this paper is to describe the design and operation of a soil core sampler that is hydraulically powered for rapidly measuring and analyzing soil physical properties.

3 N.H. Abu-Hamdeh, H.F. Al-Jalil / Soil & Tillage Research 52 (1999) 113± Fig. 2. Diagram of the soil core sampler. A soil core sampler (Fig. 1) was designed in the workshops of Jordan University of Science and Technology to overcome the dif culty to gain a coherent understanding of the soil compaction by agricultural vehicles due to the wide and confusing variety of methods used to study the subject. The hydraulic actuation of the coring probe reduces the physical effort required by the operators and the time required making measurements. In addition, more accurate data over the manual sampling method are obtained. Fig. 2 shows a diagram of the soil core sampler. It consists of a frame mounted by a tractor three-point hitch to operate in remote locations such as planted elds. The system will rapidly collect the soil samples from the ground at different depths. The major parts of the probe assembly were made of steel because of its durability. The 2.5 cm diameter steel guide rods on each side of the hydraulic cylinder maintain the direction of the coring probe in the vertical direction and protect the cylinder rod from bending. The probe assembly slides horizontally on a 1.5 cm thickness 60 cm 12 cm rectangular steel slide rail. This slide rail was welded to two adjustable height legs at each end, which are capable of raising and lowering the sampler. The legs are raised and lowered by a screw jack, powered by the PTO shaft of the tractor through a bevel gear box and a worm gears set. The gearbox is equipped with a dog clutch that engaged with either bevel gear to change from lowering to raising and vice versa. Raising the legs provide external force transmitted from the tractor to hold the frame on the ground so that the soil reaction force will not raise the frame from the ground during sampling. The coring probe was designed to hold the tapered sample tubes. The coring tube used in this design is shown in Fig. 3. The tubes were beveled on the outside to minimize compaction to the soil core during sampling and to provide a sharper cutting edge. A soil core diameter over length ratio of about one was found to work well for a variety of soil moistures and textures. The soil cores used in this design were made of aluminum with length of 5 cm and 5 cm inner diameter. This geometry provided soil cores which were self supporting and provided enough wall friction to hold the cores in the tubes during soil sampling. Making the core's diameter over length ratio smaller would tend to compress the core and underlying soil matrix due to added wall friction. Making the core diameter to length ratio larger would tend to make the core more susceptible to sliding out during the soil sampling. When coring, the sample tube is inserted straight into the soil 5 cm and then retracted straight back up. This procedure is repeated for all cores, only at successively greater depths. The coring probe on which the coring tubes are mounted during coring is shown in Fig. 4. The coring probe was in turn attached to the cylinder rod which is used to push the coring tubes straight up and down. A KUBOTA M8030 tractor was used to provide the hydraulic power to the double acting cylinder. The hydraulic system of the HPSCS, which is part of the hydraulic circuit of the KUBOTA tractor, is a closed system. The hydraulic circuit of the HPSCS system consists of a hydraulic pump with a reservoir and lter at the rear of the tractor. The hydraulic oil is transported via hydraulic lines to a 4-way, 3 position, solenoid operated, directional control valve and a pressure control valve stacked on a valve block mounted on the probe assembly. These valves operated a 3.81 cm bore by cm stroke Parkertron hydraulic cylinder that is attached directly to the coring probe. The pressure control valve is used to set the maximum pressure at the cylinder in order to minimize damage to the coring tubes when a rock or other obstruction is encountered. During operation, 10 soil cores were removed, one at a time, from each sample hole using the soil core sampler in an average time of 10 min. Thus, each core sample represented 5 cm of the 50 cm pro le. Any soil clinging to the

4 116 N.H. Abu-Hamdeh, H.F. Al-Jalil / Soil & Tillage Research 52 (1999) 113±120 Fig. 3. (a) Coring probe and tube used in the design. (b) Cross-section of soil coring tube. sides of the sample tube was wiped off and if any of the sample tubes were bent from hitting a rock, the tubes were replaced before the next use Field experiment description The experiment described below was designed to compare soil physical properties of soil samples obtained by the hydraulically powered soil core sampler with physical properties of soil samples obtained by a manually operated tool. The changes in soil physical properties caused by a two wheel drive KUBOTA M8030 tractor with 18.4 R30 tires in ated to 100 kpa with a loaded 1500 kg planter mounted on the tractor were measured. The experiment was conducted on clay loam (21% sand, 38% silt, 41% clay) soil and the traf cking was repeated to provide three passes in the same track. The soil properties beneath the center of the tire tracks and in the untraf cked area between tracks were measured using the hydraulically powered soil core sampler and by a manually operated tool. Cores used in the manually operated tool were 5 cm in diameter and 5 cm in length. Four replicated measurements at

5 N.H. Abu-Hamdeh, H.F. Al-Jalil / Soil & Tillage Research 52 (1999) 113± each depth were taken in the wheel track and between the wheel tracks. A total of 80 samples were collected using the HPSCS and another 80 samples were collected using the manually operated tool for comparison. Bulk density and total porosity for the top 50 cm were analyzed to determine how the soil responded to the tractor traf c. Wet bulk density of soil sample was obtained by weighing the known volume of the core lled with soil and then subtracts the weight of the core itself. Additional soil samples at each depth were retained for subsequent moisture content evaluation using the oven drying technique. Dry bulk density for each soil sample was then calculated using wet bulk density and moisture content values. Volume of solids was calculated by measuring speci c gravity of soil samples. Total porosity for each soil sample was measured using volume of solids, volume of water, and total sample volume. 4. Analysis of results Fig. 4. Photograph of the probe and coring tube assembly. Soil response for the KUBOTA M8030 tractor with 18.4 R30 tires in ated to 100 kpa in ation pressure with a 1500 kg mounted planter is presented in Fig. 5 for dry bulk density and Fig. 6 for total porosity. The data for each measured property were compiled and individual values were averaged for each 10 cm depth increment to a depth of 50 cm. Thus, each point on the curves represents the average of eight replicates. Fig. 5 shows how bulk density obtained by the two sampling methods was signi cantly increased due to the wheel traf c. The effect of the tractor traf c is evident down to 50 cm. A statistical analysis performed on the experimental data using MINITAB (1994) shows that bulk density under the center of the tire track is signi cantly different from the untraf- cked at all depths (p 0.1) for the two sampling methods (Table 1). The intensity of subsoil compaction increased with the number of passes by the vehicle, and with axle load. This is similar to the results obtained by Wood et al. (1993) who found that four repeated passes of a 15.2 tonnes/axle vehicle produced signi cant compaction to a depth of Table 1 Average dry bulk density by depth of the untrafficked soil and under the center of tractor tire using the HPSCS and manual sampling methods a Depths (cm) HPSCS (3 passes) Manual (3 passes) HPSCS (untrafficked) Manual (untrafficked) 10± (a) 1.30(a) 1.24(b) 1.24(b) 20± (a) 1.30(a) 1.25(b) 1.25(b) 30± (a) 1.29(a) 1.26(b) 1.25(b) 40± (a) 1.34(a) 1.27(b) 1.28(b) Average a Means represent eight measurements in each depth range. Means in rows, within a depth range, followed by the same letter were not significantly different at a 10% level using Tukey's Studentized range test.

6 118 N.H. Abu-Hamdeh, H.F. Al-Jalil / Soil & Tillage Research 52 (1999) 113±120 Fig. 5. Soil dry density in the untrafficked area and in the center of tire for loaded tractor inflated to 100 kpa using the HPSCS sampling method and by using manual sampling method. Fig. 6. Soil porosity in the untrafficked area and in the center of tire for loaded tractor inflated to 100 kpa using the HPSCS sampling method and by using manual sampling method.

7 N.H. Abu-Hamdeh, H.F. Al-Jalil / Soil & Tillage Research 52 (1999) 113± Table 2 Average soil total porosity by depth of the untrafficked soil and under the center of tractor tire using the HPSCS and manual sampling methods a Depth(cm) HPSCS (3 passes) Manual (3 passes) HPSCS (untrafficked) Manual (untrafficked) 10± (a) 51.54(a) 53.33(b) 53.16(b) 20± (a) 50.35(a) 52.92(b) 52.69(b) 30± (a) 51.21(a) 52.48(b) 52.74(b) 40± (a) 49.59(a) 52.21(b) 51.80(b) Average a Means represent eight measurements in each depth range. Means in rows, within a depth range, followed by the same letter were not significantly different at a 10% level using Tukey's Studentized range test. 50 cm. Danfors (1974) stated that axle loads greater than 6 tonnes may cause subsoil compaction to depths deeper than 40 cm. Also, Hakansson et al. (1987) reported that the experimental traf c with vehicles having an axle load of 10 tonnes caused compaction to a depth of at least 50 cm. Another analysis was performed at a 10% level of signi cance on the data obtained at each depth by the two sampling methods. The null hypothesis was that the data at each depth for the two sampling methods have the same mean. In general, there was no statistical difference among these sets of data at equivalent depths. The tractor signi cantly reduced total porosity (p 0.1) to a depth of 50 cm for both sampling methods (Table 2). Available information clearly demonstrates that the axle load is a crucial factor for the depth of subsoil compaction. After applying traf c on the soil surface, signi cant compaction has usually been observed to a depth of about 50 cm at an axle load of 10 tonnes (Hakansson, 1985; Voorhees et al., 1986). The statistical analysis showed no difference between data sets obtained by both sampling methods at each depth. The time required to sample 10 soil cores in the eld using the hydraulically powered soil core sampler was found to be 10 min on the average. 5. Conclusions The results from the eld compaction study showed that the hydraulically powered soil core sampler was capable of collecting soil samples in the eld to measure soil physical properties using the hydraulic and mechanical power available by tractor. The hydraulic actuation of the coring probe reduces the physical effort required by the operators and the time required making measurements. The average time required in the led to collect 10 soil samples, 5 cm in diameter by 5 cm in length, is approximately 10 min. The bulk density and total porosity data from this eld experiment showed that signi cant effects were present down to a depth of 50 cm due to traf cking the eld by tractor equipped with loaded seed drill mounted on it. References Danfors, B., Compaction in the subsoil. Swedish Institute of Agricultural Engineering, Uppsala, Report No. S24, p. 91. Freitag, D.R., Methods of measuring soil compaction. In: Barnes, K.K., et al. (Eds.), Compaction of Agriculture Soils, ASAE Monograph, St. Joseph, MI, pp. 47±103. Gupta, S.C., Hadas, A., Voorhees, W.B., Wolf, D., Larson, W.E., Sharma, P.P., Development of guides on the susceptibility of soils to excessive compaction, University of Minnesota BARD Report. St. Paul. Hakansson, I., Swedish experiments on subsoil compaction by vehicles with high axle load. Soil Use and Management 1, 113±116. Hakansson, I., Voorhees, W.B., Elonen, P., Raghavan, G.S.V., Lowery, B., Van Wijk, A.L.M., Rasmussen, K., Riley, H., Effect of high axle load traffic on subsoil compaction and crop yield in humid regions with annual freezing. Soil and Tillage Res. 10, 259±268. Kunnemann, D., Wittmuss, H., Soil structure defined by air permeability. ASAE Paper No , St. Joseph, ML. Ngunjiri, G.M., Siemens, J.C., Tractor wheel traffic effects on corn growth. ASAE Paper No ASAE, St. Joseph, ML. Mckibben, E.G., Introduction. In: Barnes, K.K., et al. (Eds.), Compaction of Agriculture Soils. ASAE Monograph, St. Joseph, ML, pp. 3±6.

8 120 N.H. Abu-Hamdeh, H.F. Al-Jalil / Soil & Tillage Research 52 (1999) 113±120 Morgan, M.T., Holmes, R.G., Wood, R.K., A system for measuring soil properties in the field. Soil Tillage Res. 26, 301± 325. MINITAB, Minitab Release Minitab Inc., State College, PA. Soane, B.D., Pidgeon, J.D., Tillage requirement in relation to soil physical properties. Soil Sci. 119(5), 376±384. Voorhees, W.B., Nelson, W.W., Randall, G.W., Extent and persistence of subsoil compaction caused by heavy axle loads. Soil. Sci. Soc. Am. J. 50, 428±433. Wells, L.G., Burt, E.C., Response on selected soils to power tires at disparate moisture conditions. ASAE Paper No St. Joseph, ML. Wood, R.K., Reeder, R.C., Morgan, M.T., Holmes, R.G., Soil physical properties as affected by grain cart traffic. Trans. ASAE 36(1), 11±15.