We tested the nitrogen level at Seven Bridges, comparing the soil from the beach to the soil from the woods as well as in between these two areas.  The nitrogen levels in the samples taken in the woods were significantly higher than those taken at the beach (P = 0.032). We hypothesized that there would be more nitrogen within the woods of Seven Bridges than at the beach.

Keywords: nitrogen, topsoil, soil, sand, clay, dirt, woods, beach


            Nitrogen plays an important role in the environment. Mostly, it aids plants in their growth, specifically with their leaf size to continue photosynthesis and the seed production to pass on their genetic line (Tucker, 1999). However, due to leaching, nitrogen is easily lost (O’Leary et. al, 2002). The reason for this is because of the charges between water and nitrate. When the water is passing through the soil, the nitrate is attracted to water due to the opposite charges and the gets carried away (Wiederholt et. al, 2005).  

The amount of leaching that would occur is based on the soil coarseness. Soils with a higher coarseness, such as sand, are not as compact,  and therefore allow water to pass through them. Soils with a lower coarseness, such as clay or loam, are much more compact and leave little room for water to pass through (O’Leary et. al, 2002). Based on this information, our hypothesis was that there would be more nitrogen within the woods of Seven Bridges than at the beach.

Materials and Methods

            On Thursday, November 3, 2011, we collected soil samples at Seven Bridges at 1600 hours. Earlier that day it had been raining, but when the soil was collected it had been sunny with wind. At Seven Bridges, 30 topsoil samples were collected; 10 samples being from the beach, the woods, and half way in between the beach and woods. The in-between samples were gathered along the clearly-marked vegetation line, the beach and the woods samples were both gathered 5 m into their respective locations (each being in opposite directions). Each transect of the beach-woods area was done 3 m apart. To test the nitrogen levels in each of the samples, we used the LaMotte Soil Test Kit number 5934 and followed the instructions. After getting the data, we analyzed our results in Microsoft Excel.  


            Overall there was a significant difference between the nitrogen level in the beach soil and the woods soil (Fig. 1, P = 0.032). The scale for identifying the nitrogen level is on a 1 to 4 scale, 4 being the highest amount. The average nitrogen level for the beach was 1.6 and the standard deviation was 0.84. For in between the beach and the woods the average was 1.6 with a standard deviation of 0.70. The nitrogen level for the woods was 2.4 with a standard deviation of 0.97.

Figure 1. There is More Nitrogen in Woods Soil than Beach Soil (P = 0.032)


            The results supported our hypothesis. However, we also thought that the soil in between the beach and the woods would have more nitrogen in it than the beach soil. This could be the result of the rain that happened earlier that day. Since leaching has a big effect of the amount of nitrogen that is available, it is probable that that is what affected the in-between soil nitrogen levels (O’Leary et. al, 2002). Because we only tested in one particular park, it is difficult to use this data to generalize about nitrogen levels of the soil in other places—for all we know (since we did not gather vegetation samples) these woods could be home to some sort of plant that have nitrogen-fixing bacteria in their roots.

One thing to note might be that the woods soil varied from loose dirt to compact clay. Perhaps experimenting on more samples that are of the same soil type would be more accurate. This would be the thing that we would change in this experiment: we would also gather more samples at the Seven Bridges area as well as at other parks that had the same beach and woods transition.
















Literature Cited

O’Leary, Mike; Rehm, George; Schmitt, Michael. (2002). Understanding nitrogen in soils. University of Minnesota Extension. Retrieved on November 4, 2011 from http://www.extension.umn.edu/distribution/cropsystems/dc3770.html

Tucker, M. Ray. (1999). Essential plant nutrients: their presence in North Carolina soils and their role in plant nutrition. Retrieved on November 4, 2011 from http://www.ncagr.gov/agronomi/pdffiles/essnutr.pdf

Wiederholt, Ron; Johnson, Bridget. (2005). Nitrogen behavior in the environment. Retrieved on November 4, 2011 from http://www.ag.ndsu.edu/pubs/h2oqual/watnut/nm1299w.htm