Can show different methods of farming, like step farming which is generally done in hilly regions. Or can make model showing benifits of drip irrigation system over conventional irrigation methods. And Can even possibly show some organic farming techniques like use of bettles, earth worms in place of pestisides to prevent environmental harm.

You can make a model like this- A huge Thermal power Plant deleberately Polluting the nature & agricultural Field surrounding 100 to 150 K.M by Ariel.