Effects of pH on Plant Growth
How soil pH affects plant growth
What is pH?
pH is a numeric scale used to specify the acidity or alkalinity of an aqueous solution. The scale goes from -0 (Extremely Acidic) to 10+ (Extreme Alkaline). Soil can usually range from a pH of <3.5 (Ultra Acid) to >9 (Very Strong Alkaline).
The Experiment
Hypothesis
How does pH effect plant growth? Is it bad for the soil to be too acidic or too basic? If so, at what point on the scale does it become harmful to the plant?
My hypothesis is that grass will grow best in Neutral (pH of 7-8) soil, and the others will not do very well.
Control Soil
For the control, I will plant 20 grass seeds in a pot of soil with a pH of 7, which is neutral. Pure Water has a pH of about 7.5.
Acid Soil
For one end of the spectrum, I will plant the same type and number of grass in a pot of soil with a pH of 5. Acid Rain has a pH of about 4-5.
Alkaline Soil
For the other end, I will again use the same type and number of grass in a pot of soil with a pH of 9. Baking Soda usually has a pH of about 9-10.
Now We Wait
Let It Grow
I set the three pots of soil on the windowsill and watered them regularly, so they all received the same amount of water and sunlight. I went and recorded the number of blades of grass and their average height in each pot once a week for three weeks
Week 1
Control Soil
4 Blades
Average Height: 1 cm
Acid Soil
No Growth
Alkaline Soil
6 Blades
Average Height: 2
Week 2
Control Soil
7 Blades
Average Height: 2.5 cm
Acid Soil
No Growth
Alkaline Soil
12 Blades
Average Height: 3 cm
Week 3
Control Soil
11 Blades
Average Height: 3 cm
Acid Soil
No Growth
Alkaline Soil
17 Blades
Average Height: 4.5 cm
Results
In the end, the Alkaline Soil with a pH of 9 did the best. It ended with 17 blades of grass averaging at 4.5 cm tall. Next came the Neutral Control Soil at pH of 7, with 11 blades and an Average Height of 3 cm. There was no growth in the Acid Soil at all.
Conclusion
The question for this experiment was how does pH affect plant growth. My hypothesis was that the grass would do best with neutral pH levels. I was incorrect. I found out that grass actually cannot grow at all in acidic soil, and that it actually grows best in slightly Alkaline soil rather than neutral soil.