How Stuff Works NPK Soils

Nitrogen (N): Helps make chlorophyll that gives deep green color. Chlorophyll is necessary for photosynthesis, the essential process in which plants manufacture carbohydrates (their stored energy source) from water, carbon dioxide and sunlight.

Phosphorus (P): Promotes strong root development and winter hardiness. It helps withstand environmental stress. Plants supplied with phosphorus is less likely to become diseased.

Potassium (K): Reduces transpiration (loss of water through leaves), so plants need less water when it has enough potassium. It strengthens leave and helps withstand stress.

Wikipedia on Fertilizer

Service Learning In Chemistry

Opportunities for Service.
http://studentorgs.vanderbilt.edu/vsvs/lessons.php