I'm doing a project in junior year chemistry where I get to choose what I investigate as long as it covers course content. I'm interested in exploring how quantitative (ig. incremental) change in an independent variable of soil would change some dependent variable -- particularly through experimentation.
I was thinking of seeing how changes in soil pH affect soil fertility, with specifically focusing on phosphate content to measure soil fertility for simplicity + it's the easiest (i think) to do an experiment over. However I'm not sure if there's correlation between these two variables (which wouldn't look good).
Any recommendations for independent/dependent variables with correlation + a useful for real-world application of soil chemistry to look into, where a high school level experiment could produce useful observations, would be super appreciated. That's if you think my original phosphate x pH idea wouldn't make sense.