The Effect Of pH Of Solutions On Bean Plant Growth

Distilled water has a pH of seven (neutral) and most plants grow best with a soil pH of 6, as most have adapted to places in the world with slightly acidic rain. Most plants cannot grow with a pH under six, as necessary micro nutrients for growth usually cannot survive in the acidity. The best pH solution for green beans to grow in will be tested. Water solutions’ pH is easier to control than soil pH and heavily influences the soil’s pH.

In prime conditions, green beans can germinate (develop and grow), in 7-10 days, making them ideal for my experiment as not much time is available for plant growth. Generally, green beans need to be watered regularly before they sprout and then after, only need one inch or 25.4ml of water per week. The beans will be watered once a week with 25ml of their assigned pH solution.

In order to test and adjust the pH of the water solutions, liquid universal indicator and a color chart will be used to reach a desired pH. Desired acidity will be reached with the addition of lemon juice, which has a pH of two, and alkalinity will be reached with baking soda, which has a pH of nine. The below color chart was used to indicate pH.

Plants receiving a solution with a pH of six or seven were the only beans that grew. There was a vast difference in height between pH five and six, with seven having the highest average, only slightly taller than the pH 6 solution. Both pH 8 and 9 plants did not grow. Plants watered with a pH solution of six and seven grew the tallest, as these are the most commonly found pH in nature. Plants naturally live off water which, when distilled has a neutral pH of seven, however can be more acidic due to other elements combining with it in the sky, then falling as rain, or contamination with other substances if tap water. Other alive or decomposing organisms in the soil may affect soil acidity too. These results mostly met my hypothesis, as the pH six plants did grow tall, even though the neutral pH plants overall grew tallest.

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This experiment could be improved through measuring the exact mass if soil each seed is planted in, controlling the sunlight each plant receives by using artificial lighting and using a alkaline chemical which is stronger than the pH willing to dilute it too. The pH of nine could also be change to a pH of three, which is more attainable with the addition of lemon juice. A chemical with a higher alkalinity such as lime water could have eliminated this mistake.

The aim of this experiment was achieved, as it was clear that both the pH of six and seven allow plants to grow best, with seven having the tallest plants. Although variables such as the volume of water given to each bean and the time each plant was let to grow were kept constant, there were also many other factors which were not controlled well such as the amount of sunlight each plant receives and the level of soil the beans were planted in. Although some of these factors could have been controlled better, things like amount of sunlight received were difficult to regulate as the greenhouse does not have artificial lighting and uses sunlight. The use of a 25 ml measuring cylinder to measure the water each plant received let each plant receive the most exact results possible with the equipment available to us. The universal indicator droppers made it mostly easy to indicate the pH of each solution; each batch had differing amounts of drops in them, which could affect the color the solution shows up as compared to the chart. The range of pH used in this experiment was large enough to see clearly that bean plants cannot survive or grow in extreme acidity or alkalinity and prefer to grow with a neutral pH. Thus, this experiment is predominantly invalid.

Each pH solution had four bean plants for five different solutions, meaning there were 20 beans in total. Although each bean with the pH of nine received the same solution, the baking soda would not be alkaline enough to reach pH nine before becoming saturated. Every bean was planted in germinated and planted in the same lesson, and watered together once a week. At first, all plants were to be watered on a Monday, which is when the SRP lesson was for the week, however, because of the Queen’s Birthday holiday, the solutions for the next week were made on the Thursday beforehand. The prepared solutions were given to the plants the next Thursday. The last week or growth, the beans were also watered on a Wednesday instead of Monday, as this was the assigned Project A SRP lesson. All plants were placed in the sunlight throughout the week to try maximizing sunlight exposure, although some plants at the front of the box may have received less direct sunlight than those at the back. Outliers for this experiment were difficult to eliminate as plants grow at an individual pace and vast differences in growth were the best indicator to understand the effect of the pH. There were also no outstanding outliers, as the plants were measured in millimeters, which are a relatively small unit. The results were somewhat consistent as it was clear that pH 5, 8 and 9 did not aid the growth of the plants at all, whereas pH 6 and 7 had considerable growth on all plants. All plants for each independent value were averaged. Overall, this experiment was reasonably reliable.

For every volume of water measured, the smallest cylinder possible was used, for example when measuring 100 ml of distilled water the 100ml measuring cylinder was used whereas when measuring 25ml, the 25ml one was used. The plants ultimate height or length was measured to the closest mm marked on the ruler. To eliminate the parallax error, each volume of water was measured at eye level and at the meniscus, although the plastic cylinders, which were used, did not produce a large meniscus. All millimeter measurements were recorded to zero decimal places, instead of being in centimeters to one decimal place. Some plants also grew on a curve, so to find the most accurate length; the plant was flattened to find the exact millimeter. Hence, the experiment was primarily accurate.