Effect of Traffic Rate and Type on Soil Compaction in Sandy South Georgia Soils Matt Williams and Eric C. Brevik abstract Soil compaction is one of the largest problems faced by modern mechanized agricultural and forestry operations. This makes research in the area of soil compaction critical. This study was undertaken to see how different types and levels of traffic have influenced soil compaction in sandy soils at the Valdosta State University Lake Louise field station south of Valdosta, GA. Four different traffic patterns were investigated in this study. The first area has relatively high vehicular traffic, the second more moderate vehicular traffic, and the third area a relatively low level of vehicle traffic. The fourth area has experienced foot, horse, and ATV traffic, but full sized vehicles like cars and vans have not been used in the area. To study compaction, soil cores of known volume were taken at the soil surface and at 30-cm depths. These cores were taken both in the trafficked area (road, trail) and alongside the trafficked area at three locations for each treatment. Average soil bulk density values for the trafficked and untrafficked areas were statistically compared to determine the effects of traffic patterns on soil compaction. Results indicate that soils were more compacted along trafficked areas than in the corresponding untrafficked areas with the exception of the fourth area, which had experienced the lightest traffic load.
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oil compaction is one of the largest problems faced by modern mechanized agricultural and forestry operations (Plaster, 1997; DeNeve and Hofman, 2000). Compaction occurs when soil particles are pressed together, reducing the pore space, which in turn increases the bulk density. Compaction decreases pore size, increases the proportion of water-filled pore space at field capacity, and decreases infiltration, which in turn increases runoff and water erosion (Stiegler, no date). Compaction is influenced by many factors, including traffic type and rate, the weight of the items or bodies that make up the traffic, and the area over which this weight is distributed. Because of the relationship between compaction and bulk density, one of the most common ways to determine soil compaction is through the measurement of bulk density. Soil texture is one of the most important factors influencing bulk density. The ideal soil has 50% pore space. Many compacted soils are approximately 30% pore space, which is not as efficient for air and water transport. This leads to slower infiltration and poorly aerated soils. This, in turn, limits the root growth and nutrient uptake for plants, including crops (Brady and Weil, 2002). Soils made of a uniform mixture of sand, silt, and clay usually become more compacted than soils made of the same material as a result of smaller particles filling in larger pores. Moderately coarse soils such as sandy loams are the most susceptible to compaction (Stiegler, no date). Soil water content can exert pressure on underlying soil. Water acts as a lubricant for the soil particle, so particles get compressed tighter M. Williams, Undergraduate, Dep. of Physics, Astronomy, and Geosciences, Valdosta State University, P.O. Box 447, Woodbine, GA 31569 (
[email protected]); E.C. Brevik, Associate Professor, Dep. of Natural Sciences and Agriculture and Technical Studies, Dickinson State University, Dickinson, ND 58601 (
[email protected]). Published in Soil Surv. Horiz. 51:88–91 (2010).
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and are more easily rearranged when wet than when under dry conditions. Soils can experience maximum compaction under two different conditions. One is when the moisture content nears field capacity. The other is when small and medium pores become filled with water. Organic matter also has a great influence on compaction. The higher the organic matter content of the soil, the less likely the soil is to experience compaction. Organic matter promotes larger and stronger soil aggregates. In dry conditions, aggregates stick together, maintaining larger pores. Organic matter is also much less dense than the mineral portion of the soil, so it acts as a filler in the soil without adding significant weight. Bulk densities are usually higher deeper in the soil due to the lack of organic matter and the compressive weight of overlying materials. There has been significant work done on soil compaction, yielding a deep and diverse published literature (Brevik, 2005). Some of this work includes the compaction effects of tillage (i.e., Battikhi and Suleiman, 1999), logging and forestry (i.e., Vora, 1988; Coder, 2000), grazing (i.e., Van Haveren, 1983), recreational use (i.e., Monti and MacKintosh, 1979, Stohlgren and Parsons, 1986), how compaction affects crop growth (Tu and Tan, 1991), and how the soils in historic trails have (or have not) recovered from compaction (Sharatt et al., 1998; Brevik et al., 2002). This study was undertaken to investigate compaction in sandy soils experiencing varying rates and types of traffic patterns. Such studies are important in South Georgia because the agriculture, horticulture, and forestry industries are all major economic engines in the region, and the products of all these industries can be negatively impacted by soil compaction.
Materials and Methods The study was performed at the Lake Louise Field Station, a property owned by Valdosta State University and located just to the east of
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Fig. 1. Location of the study site in South Georgia.
Fig. 2. Traffic levels on the roads and trails leading from the entrance of the Lake Louise Field Station to the borrow pit, shown as an irregular light-colored area on this air photo. Yellow, the highest traffic levels on the field station (Section 1); blue, moderate traffic (Section 2); green, light traffic (Section 3); and red, foot and ATV traffic (Section 4).
Fig. 3. From left: Fifteen-passenger vans carrying students and equipment and pick-up trucks are typical types of traffic on the first three sections of the study sight. An ATV-mounted soil probe was used to access and sample for soils studies at remote locations on the field station, including the borrow pit area via the fourth section trail access. The ATV and students carrying equipment and supplies made up the traffic along the fourth section of the study. Interstate 75 (I-75) approximately 15 km north of the Florida state line (Fig. 1). There is a borrow pit on the property that was excavated in 1961 to supply sand for the building of I-75 (Dixon-Coppage et al., 2005). The samples for this project came from the roads and trails entering the field station and running back to the borrow pit. These roads and trails were split into four sections on the basis of their differing amounts and types of traffic (Fig. 2). The first section experiences the heaviest traffic, which is primarily motor vehicle traffic (Fig. 3). The first section sees 15-passenger van, pick-up, and other vehicular traffic about once every 1 to 2 wk on average. The second section experiences the same types of motor vehicle traffic, but about once every 2 to 4 wk on average. The third section is also used by motor vehicles, but only sees traffic about once a month on average. The final section, which ends at the borrow pit, is not accessible by a full-sized vehicle. It only receives foot and ATV traffic (Fig. 3), with foot traffic making up the vast majority, and also experiences this traffic less than once a month on average. This final section is also fairly new, having been established about 5 yr before this study was conducted. The roads that experience vehicular traffic have all been established for more than 50 years. Samples were collected from three sites in each of the four sections, with four samples collected at each site (Fig. 4). The first sample was from the surface of the road in the ruts that experienced the most wheel traffic. The second sample came from 30 cm below the first. The third sample was from the surface in the woods directly across from the road sample
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Fig. 4. A site where a bulk density sample was collected at the 30-cm depth. Boot toe in the lower center part of the photograph provides scale. point, and the final sample was at the 30-cm depth in the woods. The samples from the woods were used as control samples that represented what the bulk density of these sites would be given a more or less natural setting. There were a total of 12 sites within the four sections, which added up to 48 total samples collected for this project. The collection of samples was performed with a core sampler of known volume (344.8 cm3). Samples were removed from the cylinder and placed in a zippered plastic bag, labeled, and stored in a refrigerator until the lab work could be performed. In the lab, samples were put in a beaker of known weight, placed in an oven, and baked for 24 h at 105°C. Once the samples were removed
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from the oven, they were weighed once again to find the oven-dry weight and calculate the bulk density of each sample. Microsoft Excel (Microsoft Corp., Redmond, WA) was used to conduct statistical analyses, including calculation of mean values, F-tests, and t tests.1 After the mean values were calculated an F-test was performed to find p values. If the p value was greater than 0.05, a t test for equal variances was performed. If the p value was less than 0.05, a t test for unequal variances was performed. The bulk density of the road or trail and woods samples were compared using the t tests to evaluate whether or not the trafficked samples were statistically compacted (i.e., had a statistically higher bulk density than the woods samples). Each of the four sections was then compared, again using the t tests, to see how compaction was influenced by the amount and type of traffic. Particle size analysis was performed on samples from each of the 48 sampling sites according to the sieve and hydrometer method (Gee and Bauder, 1986).
Results and Discussion Section 1, which had the heaviest traffic, had the highest bulk density at the soil surface (Table 1). The road surface bulk densities decreased with decreasing amount of traffic, with Section 4 having the lowest surface bulk density. The road surface bulk density in Section 1 was also higher than the 30-cm bulk density in all other sections except for Section 3. The woods samples had a higher bulk density at 30 cm than at the surface, which would be expected of natural soils. Therefore, using a simple comparison of means, it was found that heavier amounts of traffic compacted the surface of the soil more than lighter levels of traffic. The mean bulk density value for the surface of the trail in Section 4 was less than in the woods for Section 4, and the mean values at the 30-cm depth were equal for both the trail and the woods in Section 4. This would indicate that the traffic types and levels in Section 4 did not cause compaction.
Table 1. Mean bulk density values for each of the traffic zones. Bulk density Road Road Woods Woods Traffic zone surface 30 cm surface 30 cm Heavy (Section 1) Medium (Section 2) Light (Section 3) Foot/ATV (Section 4)
1.74 1.69 1.66 1.48
——————————— g/cm3 —————————— 1.70 1.40 1.71 1.70 1.51 1.68 1.76 1.43 1.63 1.57 1.52 1.57
in Sections 2, 3, and 4, an expected result given both the differing levels of traffic and the mean bulk density values found during this study (Table 1). Although the mean surface bulk density was higher in Section 2 than in Section 3, this difference was not statistically significant (Table 2). The lower mean bulk density value seen in Section 4 was statistically significant when compared with the other three sections. Therefore, the most heavily trafficked section and the most lightly trafficked section differed from all other sections, but the two sections with intermediate traffic patterns did not statistically differ from one another (Table 2). All soils sampled in this study had sandy or loamy sand textures, with the exception of one sandy loam from one of the Section 2 samples (Fig. 5). None of the mean bulk density values were above root-limiting values, but the mean value for the surface of Section 1 was close to root-limiting for fine sand, and the mean value for the surface of Section 2 was close to the root-limiting value for sandy loam (Stiegler, no date).
Conclusions This study indicates that traffic on the sandy soils investigated can cause significant compaction, with the amount of compaction related to the level and/or type of traffic. Greater traffic by heavier equipment led to higher bulk densities in the surface layers, and even moderate traffic levels caused significant compaction of the soil surface. However, the light foot and ATV traffic that characterized Section 4 had no significant affect on compaction as seen in this project. In addition, none of the surface soils sampled in this study had achieved root-limiting bulk density values for sandy soils. These findings provide encouraging evidence that careful management of traffic may minimize soil compaction in sandy soils such that significant loss of plant productivity due to compaction will not occur.
Statistical analysis showed that the Section 1 road surface was more compacted than the corresponding woods surface (Table 2). There was no statistical difference in the compaction at 30 cm between the road and the woods in Section 1. In Section 2 the road surface was also more compacted than the woods surface, while there was no difference at the 30-cm depth. The Section 3 road surface and 30 cm depth was compacted more than the woods surface and 30 cm depth. In Section 4, which Acknowledgments and Disclaimer only experience light traffic in the form of foot and ATV traffic, the trail surThis research was conducted when Matt Williams was an undergraduate face bulk density was equal to the woods surface bulk density, as were the student and Eric Brevik an Associate Professor in the Department of Physics, trail and woods bulk densities at 30 cm, again indicating that the lightest Astronomy, and Geosciences at Valdosta State University. traffic in this study did not cause compaction. On the whole, these results show that heavier traffic caused Table 2. Summary of p values for the t-tests comparing bulk density values.† greater compaction of the surface A B C D E F G H I J K L M N O layers of the soil. This increased B 0.023 compaction was not seen at the C 0.035 0.044 D 0.188‡ 0.354 0.017 30-cm depth within any of the E 0.048 0.335 0.048 0.280 F 0.222 0.488 0.025 0.411 0.447 sections investigated. The surface bulk density in Section 1 was statistically higher than the surface bulk densities Trade names or commercial products are given solely for the purpose of providing information on the exact equipment used in this study, and do not imply recommendation or endorsement by Dickinson State University or Valdosta State University.
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G 0.006 0.035 0.193 0.411 0.016 0.030 H 0.028 0.236 0.048 0.233 0.441 0.417 0.016 I 0.009 0.043 0.057 0.090 0.151 0.255 0.026 0.157 J 0.310 0.129 0.012 0.170 0.089 0.179 0.009 0.076 0.039 K 0.027 0.034 0.422 0.012 0.014 0.020 0.216 0.039 0.047 0.008 L 0.002 0.005 0.071 0.027 0.031 0.125 0.047 0.026 0.109 0.018 0.060 M 0.000 0.000 0.242 0.007 0.000 0.026 0.344 0.000 0.000 0.011 0.269 0.000 N 0.001 0.001 0.107 0.006 0.005 0.039 0.151 0.004 0.011 0.007 0.098 0.034 0.003 O 0.080 0.109 0.211 0.071 0.120 0.096 0.445 0.123 0.154 0.044 0.240 0.204 0.359 0.335 P 0.004 0.030 0.081 0.015 0.017 0.051 0.178 0.017 0.036 0.011 0.075 0.094 0.056 0.486 0.333 † A, heavy traffic road surface; B, heavy traffic road 30 cm; C, heavy traffic woods surface; D, heavy traffic woods 30 cm; E, medium traffic road surface; F, medium traffic road 30 cm; G medium traffic woods surface; H, medium traffic woods 30 cm; I, light traffic road surface; J, light traffic road 30 cm; K, light traffic woods surface; L, light traffic woods 30 cm; M, foot/ATV traffic trail surface; N, foot/ATV traffic trail 30 cm; O, foot/ATV traffic woods surface; P, foot/ATV traffic woods 30 cm. ‡ Value is in italics if Ho (means are equal) is not rejected.
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Brady, N.C., and R.R. Weil. 2002. The nature and properties of soils. 13th ed. Prentice Hall, Upper Saddle River, NJ. Brevik, E.C. 2005. The influence of long-term anthropogenically-induced compaction on select properties of soils in the midwestern United States. Ga. J. Sci. 63(2):122–135. Brevik, E., T. Fenton, and L. Moran. 2002. Effect of soil compaction on organic carbon amounts and distribution, south-central Iowa. Environ. Pollut. 116:S137–S141. Coder, K.D. 2000. Soil compaction & trees: Causes, symptoms, & effects. The University of Georgia, Athens, GA. DeNeve, S., and G. Hofman. 2000. Influence of soil compaction on carbon and nitrogen mineralization of soil organic matter and crop residues. Biol. Fertil. Soils 30:544–549. Dixon-Coppage, T.L., G.L. Davis, T. Couch, E.C. Brevik, C.I. Barineau, and P.C. Vincent. 2005. A forty-year record of carbon sequestration in an abandoned borrow-pit, Lowndes County, GA. Proc. Soil Crop Sci. Soc. Fla. 64:8–15. Gee, G.W., and J.W. Bauder. 1986. Particle-size analysis. p. 383–411. In A. Klute (ed.) Methods of soil analysis. Part 1. Agron. Monogr. 9. ASA and SSSA, Madison, WI. Monti, P.W., and E.E. MacKintosh. 1979. Effect of camping on surface soil properties in the boreal forest region of northwestern Ontario, Canada. Soil Sci. Soc. Am. J. 43:1024–1029. Plaster, E.J. 1997. Soil science and management. 3rd ed. Delmar Publ., New York. Sharratt, B., W. Voorhees, G. McIntosh, and G. Lemme. 1998. Persistance of soil structural modifications along a historic wagon trail. Soil Sci. Soc. Am. J. 62:774–777. Stiegler, J.H. No date. Soil compaction and crusts. F2244. Oklahoma Coop. Ext. Serv., Oklahoma State Univ., Stillwater, OK.
Fig. 5. Results of textural analysis.
Stohlgren, T.J., and D.J. Parsons. 1986. Vegetation and soil recovery in wilderness campsites closed to visitor use. Environ. Manage. 10(3):375–380. Tu, J.C., and C.S. Tan. 1991. Effect of soil compaction on growth, yield, and root rots of white beans in clay loam and sandy loam soil. Soil Biol. Biochem. 23(3):233–238.
References Battikhi, A.M., and A.A. Suleiman. 1999. Effect of tillage system on soil strength and bulk density of Vertisols. J. Agron. Crop Sci. 183:81–89.
Van Haveren, B.P. 1983. Soil bulk density as influenced by grazing intensity and soil type on a shortgrass prairie site. J. Range Manage. 36(5):586–588.
Blake, G.R., and K.H. Hartge. 1986. Bulk density. p. 363–375. In Methods of soil analysis. Agron. Monogr. 9. ASA and SSSA, Madison, WI.
Vora, R.S. 1988. Potential soil compaction forty years after logging in northeastern California. Great Basin Nat. 48(1):117–120.
Soil, Not Oil, Is Essential to Sustainability Henry Lin
The unsung hero of our planet is quiet, invisible, and hidden underground yet it gives us everyday food, feed, fiber, and fuel
The underappreciated gift from nature is fragile, sensitive, and complex yet it is the home to the largest biodiversity on Earth
The crucible of all terrestrial life is fundamental, conservable, but hard to be renewed yet it suffers increasing wounds from anthropogenic impacts
The hidden half of the world underneath our feet holds a key to global sustainability yet it has no price tag while oil holds extreme high price
However, it is soil, not oil that feeds the world and controls environmental quality
Without soil, there would be no life without soil, there would be no oil without soil, there would be no sustainability
Dep. of Crop and Soil Sciences, Pennsylvania State University, University Park, PA 16802 (
[email protected]) Published in Soil Surv. Horiz. 51:91 (2010).
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