In highly acid soils, aluminium and manganese can become more available and more toxic to the plant. Also at low pH values, calcium, phosphorus and magnesium are less available to the plant. At pH values of 6. 5 and above, phosphorus and most of the micronutrients become less available. Therefore it is of high importance that the pH remains stable and constant of 6. 5-7 for it to receive sufficient nutrients. 5. 0 Materials Potting Soil Mix Distilled Water 100mL Graduated Cylinder 18 Plastic Cups Aluminium Trays Vermiculite For Plants pH Buffer Solutions of 3, 5, 7, 9, 11 Rule Permanent Marker.
Measuring Scales Beaker 6. 0 Method 1. All necessary equipment from the materials section was assembled to conduct the experiment. 2. Holes were poked in 18 plastic cups using a compass so that drainage could occur. 3. 1 Broad-bean plant was placed in each plastic cup. 4. An ice-cream container was filled with potting mix and was mixed in with a handful of vermiculite. 5. The mixture was used to carefully fill each plastic cup containing a seedling. 6. Each plastic cup was labelled with a pH number of 3, 5, 7 or 9 using a permanent marker. There were 4 plants of each pH level and two plants used as a constant. 7.
The plastic cups containing the seedlings were placed on aluminium trays. 8. 5mL of the pH number labelled on each plastic cup was measured using a measuring cylinder and was poured into the soil surrounding the seedling. This was repeated twice a week. 9. Plants were carefully measured using a ruler and the height of each seedling was recorded, this occurred twice a week. (The seedling was measured from the soil to the top of the stem, not to the tip of the top leaves. ) The plants were weighed using scales twice a week also. 10. After 14 days, the growth was calculated by subtracting the measurement at day 1 from the measurement at day 14.
11. The average amount of growth at each pH level was found (e. g. add the heights of P1-pH 3, P2-pH 3, and P3-pH 3 and then divide by 3). 12. Results were recorded on the table “Mean Growth pH Levels. ” 13. A line graph showing the relationship between pH and growth was recorded. The pH levels were put on the horizontal axis and growth in centimetres (cm) on the vertical axis. Experimental Set Up 15th July 2011 Figure 3: Experimental Set Up Day 1 Safety Laboratory apron, safety glasses and gloves were worn while conducting experiment. Eating and drinking were banned in laboratory. Caution was taken when handling pH buffer solution.
It was not digested or and did not come into contact with skin or eyes. If this had occurred, the affected area was to be washed straight away and the teacher was alerted immediately. This was outlined in the Risk Assessment (Appendices) Variables Independent – the pH buffer solution assigned to each plant Dependent – the rate of growth of the plant including height, weight, leaves etc. Controls – potting mix, type of plant, plastic cups the plants were planted in. 7. 0 Results The following information was recorded: Weight Height Leaf Number Distance between Nodes Stem Height Compared to Total Height of Plant.
Figure 4: pH 3 Plants Final Day Figure 5: pH 5 Plants Final Day Figure 6: pH 7 Plants Final Day Figure 7: pH 9 Plants Final Day Graph 1: Height of Plants Day 1 Graph 2: Height of Plants Day 4 Graph 3: Height of Plants Day 6 Graph 4: Height of Plants Day 8 Graph 5: Height of Plants Day 12 Graph 6: Height of Plants Day 15 Graph 7: Height of Plants Day 18 Graph 8: Height of Plants Day 20 Graph 9: Height of Plants Day 22 Graph 10: Average Height of Plants Graph 11: Average Weight of Plants 8. 0 Discussion This investigation was aimed at answering what effect different pH levels have on the rate of growth of plants.
The independent variable in this investigation is the pH level (3, 5, 7, 9) and the dependent variable is therefore the rate of growth of the plant which is measured by height, number of leaves, distance between nodes, weight and stem height compared to overall height. It is clearly evident in tables 1 to 9 and graphs 1-9, that the level of pH given to each plant did have an effect on the growth rate of the plant. From the results of the experiment it was observed that the plants which were watered with a higher pH of 7 (neutral) or 9 (basic) were the pants which showed more growth.
Whereas, the plants watered with a lower pH of 3 (acidic) or 5 (acidic) showed less growth. The plants that were watered with the pH 7, (Group 3) had the highest average total growth over the three week period which was 8. 1cm. Group 4 watered with pH 9, was the only other group which showed any consistent growth, and in which all the plants survived. These plants had an average growth of 7. 847cm, following closely behind group 3. Group 3, which was watered with 5mL of pH 7, had an average total growth of 8. 1cm, only 0. 264cm more than the average of Group 4 which was 7. 847cm.
This clearly demonstrates that plants that are watered with a higher pH neutral or basic do grow higher in a shorter time, as a result of the optimum pH range was met allowing photosynthesis to occur and the plants are able to acquire the nutrients they need to grow sufficiently. Evidently these findings supported the theory that when the plant receives the most favourable pH, the enzyme for chemical reaction that enables photosynthesis to occur is most active. The findings also support that the water pH value directly affects nutrient availability, hence why when the optimum pH is met; nutrient availability to plants is high.
Thus why when plants are watered the optimum pH level, in this case 7-9, it results in maximum growth rate. It can also be seen in tables 1-9, graphs 1-9 but in particular table 10, that the plants in group 1 and 2 which were watered with a lower pH of 3 and 5 (acidic) either died or showed little growth. By watering these plants with a lower acidic pH of either 3 or 5 the enzyme activity decreased which prevented the plants from photosynthesising as well as the availability of nutrients were significantly decreased. Thus resulting in a much lower growth rate compared to plants in group 3 and group 4.
Although plant growth did not cease completely in groups 1 and 2, on average plants that were watered with a pH of 3 had a growth of3. 35cm and plants watered with a pH of 4 had a growth of 4. 025cm. It can be seen that the further away the pH is from the optimum pH is directly proportional to the rate of photosynthesis and availability of nutrients to the plant. Thus results indicate if the optimum pH for plant growth is met (7-9), the taller the plant and higher the growth rate. As can be seen in tables 1-9, the leaf count and stem length for each plant was also recorded.
However, as the experiment was only conducted over three weeks, the leaves and stems on the plants did not have adequate amount of time for these to grow substantially. Therefore no real noticeable amount of extra leaves or stems sprouting. Nodes formed, however, did not have sufficient time to develop into a stem or leaf. However the results that were obtained from the leaf count were still able to indicate what has already been established. Both Group 1, watered with pH 3 and group 2, watered with pH 5 had the lowest average leaf count of 1. 83. Whereas group 3 watered with pH 7 had a much higher average leaf count of 3.