This lesson is one in a series of related lessons to introduce students to chemistry and environmental science concepts. Activities are modeled after real-life challenges that modern farmers face while producing our food, fiber, and fuel. Labs are inquiry based and promote critical thinking skills. Other related lessons include:

• One in a Million
• Concentrate on the Solution
• Matter of Fact
• What's Your pH?
• Know Your Nitrogen

The correct amount of plant nutrients is essential for growing healthy crops. How do farmers know if a crop should be fertilized and what type of fertilizer to use?

Collecting and testing multiple soil samples is a key step in determining whether fertilizer is needed to supplement nutrient deficiencies in the soil. Farmers compare soil test results to the nutrient requirements of their crops and then decide which fertilizer, if any, should be applied. If a fertilizer is needed, farmers make precise plans for choosing the right fertilizer, amount, application method, and timing. One type of fertilizer doesn’t fit all needs. Too much of one nutrient can cause deficiencies in other nutrients. For example, applying too much magnesium can interfere with plant potassium uptake. Also, excess application of fertilizer costs the farmer money and can lead to environmental problems. For these reasons, fertilizer production, transportation, application, and storage are heavily regulated by numerous agencies in California and throughout the U.S.

The continued development of farming technology and precise management of fertilizer inputs is necessary for farmers to grow more food on less land to feed our growing population. In 1910, the discovery of the Haber-Bosch process for fixing atmospheric nitrogen gas into commercial fertilizer drastically increased the amount of food that farmers could grow. It is estimated that nearly half the world's population is dependent upon commercially produced fertilizers.

There are 17 chemical elements that are essential to plants. Of these 17, carbon, hydrogen, and oxygen are provided to plants by air and water. Carbon is the basic building block for life and is taken in by plants in the form of carbon dioxide from the atmosphere. Through photosynthesis, carbon is combined with hydrogen and oxygen to form carbohydrates. The remaining 14 elements are absorbed by plant roots from the soil and are categorized as follows:

Primary Nutrients: Nitrogen, Potassium, and Phosphorus

• These are the three most commonly deficient nutrients in the soil. After carbon, hydrogen, and oxygen, plants take up more potassium and nitrogen than any other nutrient.
• Nitrogen is used by plants to make proteins, chlorophyll, and enzymes.
• Potassium is important for efficient water use by plants because it is required to open and close stomata. Potassium is also important for root growth and formation of starch.
• Phosphorus is needed for plants to make DNA and RNA.
• Secondary Nutrients: Calcium, Magnesium, and Sulfur
• Similar amounts of these nutrients are needed as the primary nutrients but are classified as secondary nutrients since the soil is less likely to be deficient in these nutrients.
• Calcium is important in the formation of new cell walls and membranes.
• Magnesium is essential in forming chlorophyll for photosynthesis.
• Sulfur is involved in protein synthesis and the formation of nitrogen fixing nodules on legume roots.
• Micronutrients: Zinc, Iron, Manganese, Copper, Boron,
• Molybdenum, Chlorine, and Nickel
• Micronutrients are just as important to plants as the primary and secondary nutrients, but are used in much smaller amounts.