Introduction
Soil is a complex ecosystem. It is made up of minerals, organic material, gases and liquids. Soil forms the habitat for many individuals, plants, and animals. The mineral particles could be sand, clay and silt. Most soils consist of a mixture of these particles and the soil texture therefore depends on the proportions. Classification of soil is normally made according to the relative proportions of silt, sand and clay. To determine the soil type, a Textural Triangle can be used. If a fairly equal portion of each size is present then the soils is said to be a loam. Loam soils are ideal for agriculture. The sand particles ensure good drainage and a good air supply to the roots, the clay retains water and supplies nutrients, and the silt particles help to hold the sand and clay particles together.
As the world population increases and approaches 9 billion people, the pressure on natural resources is becoming more and more intense, The role of agriculture in feeding the world is extremely important. It is necessary for farmers to look towards innovation and new technologies to be more efficient. One way of doing this could be improving the quality of the soil they use to ultimately increase yields.
Bad quality soil has become an environmental issue that affects agriculture. Today, soil in some areas has virtually turned lifeless due to increased industrialisation and development. Infertile soil can cause long-term damage to populations and habitat. On example of this is the Dust Bowl that occurred in the USA in the 1930s at the same time as the Great Depression. Farmers in the 19th and early 20th century aggressively exploited the land, causing a severe ecological disaster. A large number of people were forced to relocate and abandon their farms.
Research Question
“How does the percentage of sand and clay in soil affect the growth of mung beans (vigna radiata)?”
Hypothesis
The hypothesis for this project is, as the percentages of either sand or clay increase, the growth of wheat seeds will decrease, i.e., there is a negative correlation between the two. I expect this correlation to be linear.
I have chosen this hypothesis based on the fact that plants require a fairly equal amount of sand or clay to grow, but excessive amounts of each work the opposite way and restrain plant growth.
Theoretically, clay helps retain moisture, so this should give the plant more water and facilitate its growth. However, clay can be hard for roots to push through and clay doesn’t have good drainage so roots can rot due to excess exposure to water.
Location
The experiment for this investigation will take place in the school science laboratory.
Planning
Variables
• Independent variable: Percentages of sand and clay in the different pots. To discover the relationship between the variable and prove the hypothesis
• Dependent variable: Length of mung bean shoots in millimetres, measured using a ruler.
• Control variable(s): Water, amount of soil, amount of seeds, total mass of sand and clay in each pot. These variables will be controlled to investigate the correlation between the amounts of sand and clay and the length of the shoots. The number of seeds and amount of soil must stay the same to ensure all the seeds are growing in the same conditions and to avoid flawing the result.
Equipment
The following equipment will be needed to conduct the experiment:
• Soil
• Mung beans (10 per pot)
• Sand
• Clay
• Water
• Plastic plant pots (or plastic cups)
• A balance
• A spatula
• Ruler (to measure the length of the shoots)
• Labels (one for each pot)
• Pens
• Goggles
• Lab coat
Method
1. Gather all the equipment listed above
2. Make sure you protect yourself, wear a lab coat and goggles
3. Place all the plant pots in the tray
4. Label each plant pot with the different ratios of sand to clay
5. Measure out 30g of soil and place in each pot
6. Calculate the amounts of sand and clay using the ratio
7. In the first pot (9:1), place 3g of clay and 27g of sand
8. Label each pot with the appropriate ratios
9. Repeat steps 7 and 8 until all pots are filled
10. Measure out 60g of soil and place in an extra pot. Make sure there are no traces of sand or clay in this pot
11. Label this pot ‘Control’
12. Place 10 mung bean seeds in each pot
13. Leave seeds to germinate for 2 weeks
The total mass of sand and clay was equal to 30g. I had different ratios of each for every pot, so I constructed this table to calculate the mass of sand and clay for each pot:
Clay (g)
Sand (g)
9:1
3
27
8:2
6
24
7:3
9
21
6:4
12
18
5:5
15
15
4:6
18
12
3:7
21
9
2:8
24
6
1:9
27
3
Justification
The method stated above is justified for many reasons. The location available to conduct my experiment in made it difficult to place the mung bean seeds in different locations or different temperatures. The type of seeds chosen was suitable for a school experiment because of the time it takes to germinate. The seeds were left to germinate for 2 weeks, which is a suitable amount of time in optimal conditions. Furthermore, to determine the effect of different percentages of sand and clay on plant growth, different ratios of sand to clay were used. For instance, in the first pots there was a ratio of 9:1 (i.e. 9 parts of sand to 1 part of clay). In total, the mass of sand and clay had to equal 30 g, so for 9:1, there was 27 g of sand and 3 g of clay, for 8:2, there was 24 g of sand and 6 g of clay, etc.
Safety
HAZARD
RISK
Plastic plant pots
No risk. If dropped will not break.
Sand and clay
No risk. Not harmful if in contact with skin. Wear lab coat to protect clothing.
Substances present in laboratory
Risk. Potentially harmful to skin and eyes. Wash hands thoroughly after conducting the experiment. Wear goggles to protect eyes.
Ethics
Ethics are not relevant to this particular experiment.
Results, Analysis and Conclusion
Table
Table 1 Lengths and number of shoots
Pot
Control
9:1
8:2
7:3
6:4
5:5
4:6
3:7
2:8
1:9
Number of shoots
8
4
1
5
8
3
6
8
6
2
Lengths
74
114
79
63
113
70
54
95
132
67
17
37
72
61
42
54
88
162
8
63
18
17
43
23
89
90
143
17
14
24
32
78
65
48
46
10
42
64
112
55
31
22
72
98
13
14
19
44
9
11
30
Average length
33.9
45.8
79.0
37.2
42.9
45.0
68.5
77.8
92.2
37.5
Table 2 Amount of clay and average lengths
Amount of clay (g)
0
3
6
9
12
15
18
21
24
27
Average Length (mm)
33.9
45.8
79.0
37.2
42.9
45.0
68.5
77.8
92.2
37.5
Graphs
By looking at the graph it seems there is a very weak correlation between the amount of clay in each pot and the average length of the mung bean shoots. In order to be sure of this, it is necessary to calculate the correlation coefficient.
Calculations
I am going to use for the amount of clay and for the lengths of the mung bean shoots.
is the mean of and is the mean of .
Mean:
Mean of ‘Amount of clay (g)’ ():
Mean of ‘Length of mung bean shoots (mm)’ ():
0
33.9
-13.5
182.25
-22.08
487.5264
298.08
3
45.8
-10.5
110.25
-10.18
103.6324
106.89
6
79.0
-7.5
56.25
23.02
529.9204
-172.65
9
37.2
-4.5
20.25
-18.78
352.6884
84.51
12
42.9
-1.5
2.25
-13.08
171.0864
19.62
15
45.0
1.5
2.25
-10.98
120.5604
-16.47
18
68.5
4.5
20.25
12.52
156.7504
56.34
21
77.8
7.5
56.25
21.82
476.1124
163.65
24
92.2
10.5
110.25
36.22
1311.8884
380.31
27
37.5
13.5
182.25
-18.48
341.5104
-249.48
Calculating Pearson’s Correlation Coefficient
The formula to calculate Pearson’s correlation coefficient is:
with being the amount of clay in grams and the length of the mung bean shoots in millimetres.
Using the values I calculated to find the standard deviation I found out the part of the equation:
To find the part of the equation I used the value I had calculated earlier
I then calculated the square root of this value:
Next, to find out thepart of the equation I used the value I had calculated earlier
I then calculated the square root of this value:
Using all the values I calculated previously, I substituted them into the formula:
I could also use Microsoft Excel to calculate by typing the formula ‘=CORREL’ into a cell and highlighting both columns of data.
Using this method I obtained 0.386935, so this gave me confidence in my calculations.
This value differs slightly from the one I obtained when using the formula (; the reason being I rounded my values to one decimal place.
= so there is a weak positive correlation between the two variables.
Conclusion
To investigate whether the lengths of mung bean shoots and the amount of clay in the soil are related factors, I performed Pearson’s product-moment correlation coefficient test.
Pearson’s correlation coefficient showed there was not a correlation between the two. My calculations show Pearson’s correlation coefficient was equal to 0.3867474603. This corresponds to a weak positive correlation. The test concludes that the correlation coefficient is close to zero, and at the 0.05 significance level the p-value is 0.269643 so the correlation coefficient is “not significant”. Insufficient evidence is available to conclude that there is a significant linear relationship between and because is too close to zero.
My hypothesis was that as the percentages of either sand or clay increased, the growth of wheat seeds would decrease, i.e., there is a negative correlation between the two. With the results I obtained, I cannot accept my hypothesis. Firstly, I found there was a weak positive correlation and not a negative correlation, and with the correlation coefficient being 0.3867 there was not a significant correlation between the two factors anyways.
In addition, just by observation, I could see the pot that contained equal amounts of clay and sand hadn’t grown more than pots with increased amount of sand or clay. I was expecting the pots with high amount of clay or sand to have the least growth.
Discussion and Evaluation
Discussion
In conclusion, there was a weak positive correlation between both variables, suggesting an increased amount of clay could ultimately benefit plants. This amount could be found in better quality soils that are made to improve plant growth. This is important because it shows us the amounts of clay in soil are very important for agriculture.
The conclusion to this investigation could show us that new types of soil should be engineered to increase agricultural yields. This is linked to my main environmental issue, which is feeding the world.
The link this investigation has with my second environmental issue is that knowing what minerals can improve soil quality can help prevent disasters such as the Dust Bowl and preserve the life of microorganisms that have the soil as a habitat.
Evaluations
A positive aspect of the method used was the availability and precision of the equipment. It was fairly straightforward to use and the mass of the variables was simple to measure out to ensure the experiment went well.
On the other hand, there were a few negatives to this method. The method of creating the mediums in which the seeds would grow in was difficult as it was hard to mix the clay into the soil to ensure its effectiveness. This could have impacted the growth of the seeds by giving the seeds in clay more water than that in the pots.
Furthermore, conducting the experiment in the school laboratory meant it was difficult to monitor the evolution of the plant growth, especially on weekends when the school is closed to students. It was impossible to make sure the plants were watered everyday due to restrictions and rules concerning the lab.
In addition, by using both sand and clay as a variable meant the seeds were exposed to changing environments, which meant that it could have been hard to control two variables at the same time without skewing the results.
Improvements and Future Research
In order to improve the experiment, more pots should be used. A larger number of pots would allow me to have a wider spread of data and this would make my results more statistically significant. By increasing the number of items, it increases the probability that my observations are indicative of the whole population.
Second of all, using powdered clay would make it easier for me to mix it in with the soil. With powdered clay the distribution of clay in the pot will be more equal and that could create better conditions for growth.
In addition, monitoring the plant everyday and ensuring it gets watered could also help more seeds germinate.
Applications
Solution
Farmers should start using better quality soil over soil they are usually exposed to as this can have a more long-term positive effect on their crops and their overall production. They should prioritise soils that contain significant amounts of clay, because according to this investigation, increased amounts of clay benefits plant growth. Clay contains essential minerals for plants, adds soil density and retains moisture. Growth could increase, and farmers could improve their yields, meaning they could produce greater amounts of food and eventually feed more people.
Evaluate solution
Getting better quality soil could be difficult for farmers in remote areas. These types of soil can also be very expensive, making it even more difficult to access. Geographic locations could also influence the availability of soil with clay.
More expensive soil will make the crops more expensive for consumers. This will have a domino effect. Effectively, by using better quality soil to increase their yields, farmers will face increased costs, which will force them to put prices up. In the long run this will decrease the demand of consumers and will counter act the purpose of the solution.
In addition, they should balance out the clay with sand, as clay on its own can hinder growth because it makes it difficult for roots to develop.
Bibliography
Websites:
5 ORGANIC GARDENING BENEFITS WITH CLAY SOIL | DOITYOURSELF.COM
Doityourself.com. (2016). 5 Organic Gardening Benefits With Clay Soil | DoItYourself.com. [online] Available at: http://www.doityourself.com/stry/5-organic-gardening-benefits-with-clay-soil [Accessed 21 Jan. 2017]
DUST BOWL – FACTS & SUMMARY – HISTORY.COM
HISTORY.com. (1991). Dust Bowl – Facts & Summary – HISTORY.com. [Online] Available at: http://www.history.com/topics/dust-bowl [Accessed 21 Dec. 2016]
ESTIMATING SOIL MOISTURE
Oneplan.org. (2016). Estimating Soil Moisture. [Online] Available at: http://www.oneplan.org/Water/soil-triangle.asp [Accessed 21 Dec. 2016].
FEEDING THE WORLD – AND SAVING IT | AGROLAC 2025
Agrolac2025.org. (2016). Feeding the World – And Saving It | AgroLAC 2025. [Online] Available at: http://agrolac2025.org/feeding-the-world-and-saving-it/ [Accessed 21 Dec. 2016].
HOW DOES CLAY AFFECT PLANT GROWTH
Answers.com. (n.d.). How does clay affect plant growth. [Online] Available at: http://www.answers.com/Q/How_does_clay_affect_plant_growth?#slide=6 [Accessed 21 Dec. 2016].
STATISTICAL CORRELATION – STRENGTH OF RELATIONSHIP BETWEEN VARIABLES
Explorable.com. (2009). Statistical Correlation – Strength of Relationship Between Variables. [Online] Available at: https://explorable.com/statistical-correlation [Accessed 21 Dec. 2016]
QUICK P VALUE FROM PEARSON (R) SCORE CALCULATOR
Socscistatistics.com. (2017). Quick P Value from Pearson (R) Score Calculator. [online] Available at: http://www.socscistatistics.com/pvalues/pearsondistribution.aspx [Accessed 22 Jan. 2017]