pH of Soil
The pH level of the surrounding soil can have extreme results on the growth rate and overall health of a plant. The pH is technically defined as the negative base ten logarithm of the effective hydrogen ion concentration in gram equivalents per litre. It is measured on a scale of 1-14, with each reading being shown as an acid, base, or a neutral solution. If the measurement is less than 7, it is considered an acid. The plant sorrel grows best in the acidic pH conditions of 5.5 – 6.8. The pH of the soil for each line transect created must be the same for the whole 28 m length tested for each. Variation in my pH results limits the validity of my data as it influences the height of sorrel. pH influences availability of certain nutrients such as phosphate availability which is low on acid soils. Soil samples are taken from each transect at 1m 13m and 28m. Back in the laboratory barium sulphate and indicator solution are added to the samples and ph is worked out.
Soil Temperature
Soil temperature plays an important role in many processes, which take place in the soil such as chemical reactions and biological interactions. Soil temperature varies in response to exchange processes that take place primarily through the soil surface. These effects are propagated into the soil profile by transport processes and are influenced by such things as the specific heat capacity, thermal conductivity and thermal diffusivity. Soil temperature affects water and nutrient uptake. Biological enzymes work best at certain temperatures, if enzyme optimum temperature is exceeded or not reached this could limit the rate to which the enzyme is working limiting the growth and in turn the height of the plant sorrel.
Soil temperature has a major effect on the breakdown or decomposition of soil organic matter. This organic component of the soil system is a major reservoir for phosphorus, sulphur, and nitrogen. Approximately 90% of the total amount of sulphur in soil is found in the organic matter. So, if decomposition is slowed, the ready availability of some nutrients necessary for crop growth can be restricted early in the growing season restricting plant growth.” Soil temperature (˚C) readings are to be taken with the use of a soil thermometer and then recorded on a table.
Preliminary Investigation
A day before my data collection, I visited Plain Mounds and gathered some preliminary data. My preliminary data was carried out to help me find the sites that should be tested and the distance of each line transect. Initially before preliminary data a 37m line transect was chosen, however, once I experienced the site a 28 m distance was most appropriate as there is no significant variation after the 28m in sorrel height; therefore it would be pointless and time consuming to carry it over a larger distance.
Preliminary Investigation Method:
- A line transect created over a distance of 28m.
- Tape measure placed flat along the ground vertically. Stretch tape to cover 28m in a straight line along site investigated.
- Data readings for soil temperature, light intensity, soil pH, soil compression and sorrel height at 1m, 13m and 28m.
- Soil compaction measurements taken using a penetrometer My readings were taken 1cm at a 90˚ angle at each interval to the left of the line transect. The scale was set to 0 by moving the ring to the handle, the spike was then pushed vertically into the ground until the indention is level with the surface of the soil. The handle was released and then the results were read off the scale on the side of the penetrometer.
- The soil thermometer was placed at a 90˚ angle 2 cm away to the left of the line transect at every interval.
- Place a 1m long ruler across the line transect at a 90˚ angle this way I can work out which sorrel plant is closest to the line transect. Once this was worked out, a 30cm ruler was used to measure the sorrel height in its natural position.
- Light meter measures the light intensity. Place the sensor at a 90˚ angle next to line transect where the sorrel plant is growing. Value in lux read off the scale.
- Use auger to gain 10cm² sample at the 3 intervals. Twist auger in a clockwise direction whilst pushing down; the soil sample taken must be then placed into soil bags and taken to the lab for further testing of pH.
- Record data on pre prepared table.
- In lab to work out pH of soil:
- 1cm² of each soil sample was placed into separate test tubes. 1cm² of distilled water was added to each test tube. After distilled water added, 1cm² Barium Sulphate was added to each test tube. Finally indicator was added to each test tube and pH was tested and found out by comparing to a pH scale.
A systematic stratified approach was decided as my ideal sampling technique. Systematic sampling is when samples are taken at fixed intervals, usually along a line. This normally involves doing transects, where a sampling line is set up across areas where there are clear environmental gradients. Systematic sampling is my chosen method of sampling for my investigation as I am investigating the changes of plant species as you move along a gradient. Stratified sampling was used as we were comparing 4 different subdivisions within Plain Mounds. Systematic Stratified is the combination of these 2 sampling techniques; it’s my preferred sampling technique as it avoids bias and for each sample collected the same approach is followed. this now seemed unnecessary due to little variation after 28m. The start point of the line transect was set to where variation in ground begins.
Apparatus:
Method:
- Create a line transect, open up tape measure up to 28m.
- Place tape measure flat along the ground vertically. Stretch tape measure to cover 28m in straight line along site that we are investigating.
- Take data readings for soil temperature, light intensity, soil compression and sorrel height at 1m, 4m, 7m, 10m, 13m, 16m, 19m, 22m, 25m, and 28m.
- Soil compaction measurements taken using a penetrometer which measures the force needed to push the spike into the ground. My readings were taken 1cm at a 90˚ angle at each interval to the left of the line transect. The scale was set to 0 by moving the ring to the handle, the spike was then pushed vertically into the ground until the indention is level with the surface of the soil. The handle was released and then the results were read off the scale on the side of the penetrometer.
- The soil thermometer was placed at a 90˚ angle 2 cm away to the left of the line transect at every interval.
- Along the line transect at each interval a metre long ruler is placed across the line transect at a 90˚ angle this way I can work out which sorrel plant is closest to the line transect. Once this was worked out, a 30cm ruler was used to measure the sorrel height in its natural position.
- Light meter measures the light intensity. Place the sensor at a 90˚ angle next to line transect where the sorrel plant is growing. Value in lux read off the scale. Move away from sensor so your shadow doesn’t affect lux value.
- Take soil samples at 1m, 13m and 28m to calculate soil pH. Use auger to gain 10cm² sample at the 3 intervals. Twist auger in a clockwise direction whilst pushing down; the soil sample taken must be then placed into soil bags and taken to the lab for further testing of pH.
- Record data on pre prepared table.
- In lab to work out pH of soil:
- 1cm² of each soil sample was placed into separate test tubes. 1cm² of distilled water was added to each test tube. After distilled water added, 1cm² Barium Sulphate was added to each test tube. Finally indicator was added to each test tube and pH was tested and found out by comparing to a pH scale. 3pH readings gained at each of the 4 sites.
- Repeat the steps for the 4 subdivisions within Pillow Mound.
Risk Assessment:
Risk is the probability of harm actually taking place. A hazard exists where situation has a built-in ability to cause an adverse effect. At the site Pillow Mound in Epping Forest, a few risks were associated with my investigation.
- 8 pieces of equipment needed to be carried with me to the site to help with this and limit the risk of me tripping up with all the equipment in my hand, a tray was used to place all the equipment needed for the investigation.
- The sites surface was very uneven at all the areas that were tested within plain mounds. To control the hazard I had no other option but to take my time with walking across the field. Taking my time and making sure I was looking where I was stepping ensured this hazard was avoided.
- Slippery surfaces and deep muddy areas were also an issue to avoid this specific hazard wellington boots were worn. Strong boots may prevent twisting of ankle.
- Gathering pH samples with the auger meant there was a risk of causing injury to my wrists, to help with the turning of the into the ground another auger was placed in the top of the one in the ground making it easier to rotate the auger by creating a handle.
- When testing soil pH samples, gloves had to be worn to avoid contact with the barium sulphate. Safety goggles and lab coats also used to protect the eyes and the skin.
- After the soil pH has been tested the remaining soil is then placed into a compost bin.
Analysis:
The scatter graph shown in figure 1.1 shows how soil compression affected the growth of sorrel. The data inputted into this graph was averages of the data collected for soil compression (Kg) and sorrel height (cm) from the 4 subdivisions investigated and tested at Pillow Mound.
The graph shows a clear negative correlation between soil compression and sorrel height. As soil compression increases it is evident that sorrel height decreases. The largest sorrel growth on average was 0.0975 cm and this was with a soil compression of 1.575 kg, my lowest sorrel growth recorded from my results was 0.0011cm with a soil compression of 3.6 kg.
As sorrel height isn’t constantly decreasing with increasing soil compaction it was appropriate to further my understanding and calculate how strong the relationship between my independent variable, soil compaction and dependent variable sorrel height was. This would also help me establish whether the data was causational or correlational.
Spearman's rank correlation coefficient is a measure of between two . It assesses how well the relationship between two variables can be described. It makes no assumption about data distribution. The value for rs is between +1 and -1, where +1 indicates a strong positive correlation, -1 indicates a strong negative correlation and 0 indicates no correlation at all. The data gathered at all 4 sites indicates a strong negative correlation between soil compression and the height of sorrel. The rs value gathered for my averages was -0.89 and this is greater than the critical value for 10 data sets at the 99% significance level. Therefore we can be 99% sure that soil compression restricts sorrel height and I can subsequently reject my null hypothesis establishing that causational relationship between the 2 variables is present.
Conclusion:
The purpose of this coursework was to find out about the impact which visitors have had on Epping Forest and how the subsequent soil compaction affects sorrel growth. Epping Forest has recreational, aesthetic and educational values, so is a perfect place for visitors. Considerable damage has probably been caused to the environment due to the large number of visitors. Soil compaction at Pillow Mound was relatively high probably due to human interference. Figure 1.0 showing the averages shows us that at 1m, the mean soil compression was 4.175 Kg whilst at 28m the mean soil compression was 1.575 Kg. Figure 0.9 also shows that at 1m at Site 4 soil compression exceeded 4.5 Kg.
Management of the site is being introduced with the building of car parks, an information centre, and even a ditch next to the car park to stop the cars getting onto the grass. Epping Forest is one of a number of open spaces around London owned and managed by the City of London as part of its commitment to sustaining a world class city and for the conservation of wildlife and historic landscape.
The investigation of how soil compaction affects the height of the plant Sorrel was gratifying as a correlation between soil compaction and Sorrel growth was determined. A slight flaw which may have had an impact on my results was the fact average light intensity increased slightly with increasing distance along the tape measure. At 1m light intensity was at 1894.25 Lux, at 28m this had increased to 1900.25 Lux with the Lux value fluctuating over the 28m distance. Although the differences in light intensities are little, my results are limited slightly as light intensity affects plant growth. The higher the light intensity the higher the plant growth. Light plays a major role in photosynthesis which is a 2 stage process involving the light dependent stage and light independent stage which could continue in the dark. When a photon of light hits a chlorophyll molecule the energy is transferred to the electrons of that molecule. The electrons are excited and raised to higher energy levels. If an electron is raised sufficiently it is picked up by an electron acceptor and results into ATP production via cyclic and non-cyclic phosphorylation. ATP is formed supplying the energy needed for synthesis of carbohydrates and the electron is passed along Electron Transport Chain (ETC). The differences in Lux are relatively minuscule along the line transects and so it is not sufficient enough to make my results invalid. Data collection was carried out in the morning before the sun had fully risen, as time passed and data was collected at each interval the sun carried on rising thus explaining the small differences in light intensity. In hindsight data collection should have happened at each interval at each of the 4 sites simultaneously, however, this was not viable as there were not enough people available to assist with data collection.
My hypothesis that the greater the soil compaction, the lower the height of the Sorrel plant, has proved to be correct. This is due to the fact that soil compaction doesn’t provide adequate space for the roots of the sorrel plant, which subsequently means that the plant cannot get enough nutrients, water and minerals from the soil which are needed for optimum growth. By using Spearman's rank correlation coefficient this was worked out and we are 99% certain that a negative correlation exists between the 2 variables. 4 different sites were tested at Pillow Mound in Epping Forest, and my Spearman’s rank correlations for each site indicated a strong negative correlation. To back up my hypothesis even further my preliminary data indicate a negative correlation between Sorrel height and soil compaction. 10 samples were collected along each transect so we could get an RS value for spearman’s rank that was 99% reliable and not down to chance.
Evaluation
My investigation was highly edifying and although I came to the conclusion that there is a 99% chance that soil compaction affects sorrel height proving my hypothesis correct, in hindsight I would make a few crucial amendments to my method and investigation so next time I carry out the investigation I will have an even higher level of confidence in my results.
The 4 subdivisions at Pillow Mound were investigated to gain a general overview of the site. By testing one site, we are limiting our data as our results may only be conclusive for that part of Plain mounds.
When collecting data light intensity values varied as the values could not be all taken at the same time. To avoid this more people could help with the fieldwork and we could simultaneously gain figures for light intensity at the same time. To do this more light meters would have to be provided.
Time constraints were also a major issue. We were given around 3 hours to collect our fieldwork from 4 different sub divisions within Pillow Mound. Without time constraints there would be less pressure to complete the fieldwork within a specific time leaving us enough time to gather data with each instrument.
Ideally a longitudinal study would be most ideal as the patterns established from the data was from only 1 day in the whole calendar year. Throughout the year, sorrel height will vary. The day my data was collected may not depict an average day in Epping Forest and so my data is invalid. A longitudinal study is ideal so we can collect data over the year and see how sorrel height varies. To increase data reliability we could collect data for soil compaction and sorrel height every 3 months at the same 4 subdivisions and see if there is any significant correlation. The weather would also have an effect on sorrel height; if it rains soil will be more compact and soil infiltration would not occur as rapidly. This in turn could affect seed germination as roots cannot penetrate lower soil layers. I expect plant height to be higher in the spring as spring provides optimum temperatures for seed germination, aswell as the fact that it doesn’t rain as much during spring as it does winter, so soil will not become drenched allowing the roots to penetrate the soil greater and greater foundations allows a better uptake of minerals and greater sorrel growth.
The most helpful modification would be to carry out this investigation on a different site within Epping Forest; this could show a clear contrast to how sorrel height varies with soil compaction. The data gathered in this study could only be relevant for Pillow Mound, so broadening our study to more than 1 site could further enhance data validity and reliability. Further investigations possibly using 2 paths at each subdivision could further validate data.
As a pH probe was not available at the field centre, to measure pH of the soil we had to add a spatula full of barium sulphate as well as 1cm³ of distilled water to 1 cm³ of each soil sample in separate test tubes. The amount of barium sulphate added or the amount of soil sample added to each test tube would affect pH and so our pH values could vary due to human error and the variable wasn’t of constant of using the same formula each time. A pH probe would eliminate human error and the same procedure could have been kept throughout and been kept constant.
