The students use the mixture to fertilize the soil instead of buying chemical fertilizers that could harm the environment.

VOA: special.2009.04.14

But he says many parts of the world use too much nitrogen fertilizer, and that harms the environment.

VOA: special.2011.04.05

They teach the need for farming to improve the environment and make good use of natural resources.

VOA: special.2009.04.14