Abstract

In this study, we examined soil samples for three different sites on the campus of LSU. Six soil samples were taken at each site at two depths, one at three inches and one at six inches. Two of these samples were taken directly on the path, two at five feet from the center of the path, and two at ten feet from the center of the path. The three sites were chosen because of the heavy foot traffic and the presence of a well worn path. The samples were then weighed, dried, and weighed again. We used these measurements to calculate the bulk density, gravimetric water content and the volumetric water content. From these results we concluded that soil compaction is usually less as the distance for the path increases and in the soil closest to the surface.
 

Introduction

Soil compaction is commonly referred to as the volume change produced by rolling, tamping, or vibrating the soil (Bradford and Gupta, 408). By determining soil compaction we can better understand the affects of the amount of traffic on a soil surface. In determining soil compaction the bulk density of soil, which is the ratio of the mass of dry soil to the bulk volume of the soil, needs to be measured. The bulk density of soil varies with the structure of the soil and the amount of packing (Blake and Hartge, 363). By measuring bulk density the water content of soil can be determined. Once water content is known, the relationship between the two shows how compact the soil is. This is particularly important in understanding root growth of plants and how compaction affects the moisture content of soils (Bradford and Gupta, 480).

The purpose of our study was to determine the effects on soil compaction as the distance from heavily walked paths increases along with the depth of the soil. Objectives of our experiment were to determine soil compaction by measuring the bulk density, gravimetric water content, and volumetric water content of soil samples from different paths on the campus of LSU. Common causes of soil compaction are “trampling by livestock and pressures imposed by vehicles and tillage equipment” (Bradford and Gupta, 480). From our results we hope to conclude that repetitive foot traffic in one area is also a common cause of soil compaction.
 

Materials and Methods

For taking the soil samples from the different sites, we used a core sampler with a thin-walled cylinder. The dimensions of the sample can were 4.75 cm in depth and 6.35 cm in height and it had a volume of 112.47 cm³. The first samples were taken at a depth of 3 inches, and the second samples at a depth of 6 inches. Before taking the sample all organic matter such as grass and leaves were removed to expose the soil surface.

Once the samples were taken, the soil was transferred to a can, which had previously been weighed, for drying. Before drying, the soil samples and the cans were weighed. Next, the samples were dried in an oven at 115 ^OC for one week. After drying the samples, each was weighed again. We then used the information gained from the differences in the moist soils and the oven dry soils to calculate the bulk density, gravimetric water content, and the volumetric water content of the soils used in the experiment. Formulas used in for the calculations were:

Bulk Density = [Moist soil mass (g) - Oven dry soil mass (g)] / Volume of sample (cm³)

Gravimetric Water Content = [Moist soil mass (g) - Oven dry soil mass (g)] x 100 /
                                                                Oven dry soil mass (g)

Volumetric Water Content = [(Moist soil mass (g) - Oven dry soil mass (g)) / (1g / cm³)] /
                                                                Volume of soil sample (cm³)
 

Results and Discussion

The results of our experiment along with the data we collected are shown in the accompanying table. From these results we concluded that our initial hypothesis did not apply to all cases. In half of the samples the bulk density increased as the distance from the path increased, and overall, the bulk density increased as the soil depth increased. From our experiment we also concluded that no definite relationship could be found between the distance from the walking path and the moisture content of the soil expressed as either gravimetric or volumetric water content. In some cases the water content increased, but in other cases it decreased as the distance from the path increased. However, we did find that the water content was greater at the 6 inch depth of soil then the 3 inch depth in almost all cases.

Even though the results of our experiment did not prove that the compactibility of soil is always greatest in areas were the foot traffic is highest, we do not feel this hypothesis should not be discarded. Our determination of compactibility relies on our findings of bulk density and moisture contents. However, according the Methods of Soil Analysis Part 1, bulk density varies with the soil structure (Blake and Hartge, 363). It is also known that soil compaction is frequently the cause of “momentary load application caused by rolling, tamping, or vibration” (Bradford and Gupta, 480). Based on this knowledge we cannot say that foot traffic is not a major cause of soil compaction, because we do not know the history of the soil at the sites we collected the soil from. It is highly possible that any of these soils have been compacted by heavy machinery, such as trucks, during construction or by maintenance workers.

For someone to accurately study the relationship between soil compaction and foot traffic, variables such as differences in soil structure and previous compaction would need to be controlled, or at least known. Ideally an isolated test site where these conditions could be monitored is needed before scientific conclusions could be drawn. Even though we were not able to establish a direct link between soil compaction and foot traffic we believe our results foster a more comprehensive study of their relationship.
 

Literature Cited

Blake, G. R., and K. H. Hartage. 1986. Chapter 13. Methods of Soil Analysis. Part 1. Physical and Mineralogical Methods. 2nd Ed., American Society of Agronomy, Inc. and Soil Science Society of America, Inc., Madison, Wisconsin (USA).

Bradford and Gupta. 1986. Chapter 20. Chapter 13. Methods of Soil Analysis. Part 1. Physical and Mineralogical Methods. 2nd Ed., American Society of Agronomy, Inc. and Soil Science Society of America, Inc., Madison, Wisconsin (USA).
 

Table: Data and Results of Soil Compaction Study
 

Location	Depth  (in)	Distance (ft)	Moist Soil  Mass (g)	Oven Dry Soil Mass (g)	Bulk Density (g/cm3)	Gravimetric Water Content	Volumetric Water Content
Tureaud	3	On Path	244.09	215.8	1.92	28.29%	0.25
Tureaud	3	5'	174.18	157.22	1.4	16.96%	0.15
Tureaud	3	10'	177.18	157.08	1.4	20.87%	0.19
Tureaud	6	On Path	152.44	131.13	1.17	21.31%	0.19
Tureaud	6	5'	198.44	177.11	1.57	21.33%	0.19
Tureaud	6	10'	190.61	168.33	1.5	22.28%	0.20
La Business	3	On Path	154.47	136.51	1.12	27.96%	0.25
La Business	3	5'	182.48	163.54	1.45	18.94%	0.17
La Business	3	10'	179.8	152.69	1.36	27.11%	0.24
La Business	6	On Path	186.23	159.69	1.42	26.48%	0.24
La Business	6	5'	204.11	181.99	1.62	22.12%	0.20
La Business	6	10'	207.47	173.65	1.54	33.82%	0.30
Forestry Bldg	3	On Path	167.25	154.45	1.37	12.80%	0.11
Forestry Bldg	3	5'	201.35	180.86	1.61	20.49%	0.18
Forestry Bldg	3	10'	143.78	122.57	1.09	21.21%	0.19
Forestry Bldg	6	On Path	230.84	206.21	1.83	24.63%	0.22
Forestry Bldg	6	5'	196.89	175.19	1.56	21.70%	0.19
Forestry Bldg	6	10'	204.53	179.14	1.59	25.39%	0.23

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