Explain to students the various techniques used in modern farming. These will include the use of chemical fertilizers for higher yields, deep plowing to mix the soil, use of pesticides and herbicides to protect the crops from insects, and other such practices. Emphasize upon students the fact that modern farming does lead to larger food production, but it also, in the long run, brings about a host of environment related problems which could impact the future of mankind. After students have understood the relation between present day agricultural practices and resulting environmental imbalances, have them imagine themselves as future farmers who are faced with a depleted landscape with very little or no cultivable land, polluted water sources, and a growing population to feed. Having created such a scenario, re-emphasize upon the students that the solution to such a bleak future lies in maintaining a proper balance between agriculture and environment.
Agriculture is vital for human existence, but so is our environment.
Both have to be protected for perpetuity. Ask students to imagine a scenario where agriculture is almost non-existent and then have them think about alternative food sources.