Corn

We have one of the few experimental fields here in Halle. They do experiments with different fertilizers for example. The most famous experiment is the eternal rye trial which has been going on since 1878.
If you're interested to know more; Julius Kühn field

Here on the left grows corn but the ground hasn't been fertilized in about 50 years. And on the right grows corn that is fertilized with stable muck (dung) for about the same amount of time but the amount varies.

I find the difference in growth and colour of the corn very interesting.