In this lesson, students will understand concepts about solutes, solvents, and parts per million as they learn how fertilizer solution is properly calculated and applied. Grades 6-8

dilution: the process of lowering the concentration of a solution by adding a solvent

mixture: combination of two or more different substances that are not chemically bonded and can be a solid, liquid, or gas

nutrient: a substance that provides nourishment essential for growth and the maintenance of life

parts per million (ppm): a unit of measurement commonly used to describe the nutrient concentration in fertilizer solutions; can also be used to analyze contaminants in food, groundwater, air, and more; compare to one drop of water in a swimming pool

saline: salty

solute: the substance dissolved in a solvent to form a solution

solution: a type of homogeneous mixture in which the particles of one or more substances (the solute) are distributed uniformly throughout another substance (the solvent)

solvent: a liquid in which substances (or solutes) are dissolved forming a solution

This lesson is part of a series called, Too Much? Too Little? created to introduce middle school students to the connection between soil nutrients and the food they eat. The lessons consist of a series of demonstrations and hands-on experiments that show that plants require nutrients in certain quantities. The lesson series allows students to investigate soil properties, learn how to properly prepare fertilizer nutrient solutions, identify deficiencies in plant nutrients using a key, and much more. Other related lessons include:

• Plant Parts and Functions: Anatomy and physiology of a plant.
• Digging Into Nutrients: How plants obtain nutrients from the soil.
• The Right Solution: How fertilizer solution is properly calculated and applied.
• Can We Have Too Much of a Good Thing?: Effects of applying too much or too little fertilizer.
• The Right Diet for Your Plants: Read fertilizer labels and choose the best fertilizer.
• Let's Vote On It: How soil nutrients effect local communities and economies.
• It's a Dirty Job: How earthworms benefit soil.

Fertilizers are used to provide nutrients that are not present in soil in amounts necessary to meet the needs of the growing crop. Plants can tolerate a wide range of watering and nutritional conditions, but for a commercial farming operation it is important to maximize production while minimizing environmental impact. Optimum watering and nutritional conditions vary depending on a variety of factors, including plant species, stage of life cycle, climate, and environmental conditions. Many growers purchase fertilizer in a concentrated solid or liquid form. The fertilizer is then mixed with water to create a fertilizer solution that can be applied to plants.

When fertilizer is applied in the field, farmers will calculate nutrient requirements in pounds per acre. However, in greenhouse production, the industry standard is parts per million. Greenhouses are often used for growing flowers, vegetables, fruits, and transplants. Greenhouses allow for greater control over the growing environment of plants. Depending upon the type of greenhouse, key factors that may be controlled include temperature, light, water, fertilizer, and atmosphere.

Proper fertilization of greenhouse plants is essential for producing a high-quality crop. Some nutrients (such as calcium and magnesium) may be mixed into the growing medium, or soil, prior to planting, but most of the nutrients are applied after planting using water-soluble fertilizers. Fertilizer injectors are used by most growers to deliver fertilizer to plants. These devices inject a small quantity of concentrated fertilizer into the irrigation line so that the solution leaving the hose is diluted to the proper concentration. Fertilizer injectors can be set at different ratios depending upon the needs of the plants. If the injector ratio in a greenhouse operation is 1:100, the injector delivers one gallon of fertilizer concentrate with every 99 gallons of water (one part out of 100 parts is concentrated fertilizer).

1. Ask the class if they have ever used a powdered concentrate to create a beverage such as hot chocolate or fruit punch. Explain that whether they realized it or not, they were creating a mixture. A mixture is a combination of two or more different substances, which are not chemically bonded, and can be a solid, liquid, or gas. Explain that there are two types of mixtures: homogeneous (also called solutions), which are uniform and particles are not typically seen, and heterogeneous mixtures, which are not uniform and the particles can be seen.
2. As a demonstration, add two tablespoons of salt to a 250 ml beaker of water and stir. Explain that the mixture is a homogeneous solution, meaning that the molecules within the solution—in this case water and table salt—are evenly distributed and look the same throughout.
3. In another beaker add two tablespoons of sand to 250 ml of water and stir. Have students compare and contrast the two mixtures. Ask student to describe the difference between the sand and water mixture and the salt and water mixture. Explain that the sand and water mixture is a heterogeneous mixture, meaning that the molecules will not be evenly distributed throughout the liquid.
4. Explain that in agriculture, fertilizer solutions are one way that farmers supply their crops with essential plant nutrients. In science terms, the solute is the fertilizer added to the water. The water is the solvent, which does the dissolving. The solution, more or less, takes on the characteristics of the solvent. The concentration of a fertilizer solution is defined by the amount of fertilizer (solute) dissolved in water (solvent).

1. Ask students to raise their hands if they’ve ever heard the term “one in a million.” Discuss what the term means and why people say it.
2. Build on the classroom discussion by explaining how unique “one in a million” really is. Show students a “One in a Million” Becker Bottle (Flinn Scientific, Inc.) to illustrate the concept. This three liter bottle contains one million tiny colored spheres. Each colored sphere represents a different quantity, or concentration. The yellow spheres represent 100,000 in a million, the red spheres represent 10,000 in a million, the white spheres represent 1,000 in a million, the pink spheres represent 100 in a million, and the green spheres represent 10 in a million. The single black sphere in the bottle represents one in a million, or in scientific terms, one part per million. Explain that today the class is going to investigate the scientific concept of “parts per million”—a unit of measurement used to describe a very small amount of material.
3. Explain that in the scientific community, parts per million is expressed as “ppm.” Parts per million is the unit of measurement commonly used to describe the nutrient concentration in a fertilizer solution. It can also be used to analyze contaminants in food, groundwater, air, and more.
4. Introduce the lab by explaining that students will use a dilution activity to create and investigate solution concentrations. Review laboratory safety instructions. Distribute and review the The Right Solution lab worksheet. Divide the class into pairs or triads, and direct students to the necessary materials.
5. After students complete the dilution lab activity and The Right Solution lab worksheet, use a classroom discussion to debrief their findings. Discussion points may include:
   • Good fertilizer practices that match fertilizer inputs to crop nutrient requirements will achieve high-quality, economically sustainable yields that reduce negative environmental impacts. Arable land available for growing food will continue to diminish as population growth continues. Efficiently managing inputs, such as water and fertilizer, will be essential to feeding a growing population.
   • Improperly applied fertilizer can lead to environmental problems. It is important for anyone who applies fertilizer to follow application instructions. Farmers and researchers are  constantly testing and implementing new methods for high precision use of fertilizers.
   • Fertilizer is expensive. It is in the farmer’s best interest to apply the correct amount of fertilizer, supplying the plants with only the nutrients they need.

ELL Adaptations

• Create a Venn diagram to capture the differences and similarities of homogeneous and heterogeneous mixtures.
• Use an overhead projector to demonstrate complex math problems.

After conducting these activities, review and summarize the following key points:

• Soil is a valuable and limited resource that is necessary for the proper growth of plants that provide our food and fiber.
• Farmers and ranchers use many methods to monitor and maintain soil nutrients.
• Fertilizers help plants grow to their greatest potential. They must be applied properly.

This lesson was updated in 2013 with funding from California Foundation for Agriculture in the Classroom and a grant from the California Department of Food and Agriculture’s Fertilizer Research and Education Program. The Fertilizer Research and Education Program (FREP) funds and facilitates research to advance the environmentally safe and agronomically sound use and handling of fertilizer materials. FREP serves growers, agricultural supply and service professionals, extension personnel, public agencies, consultants, and other interested parties. FREP is a part of the California Department of Food and Agriculture (CDFA), Division of Inspections Services.

Editor: Shaney Emerson
Executive Director: Judy Culbertson
Illustrator: Toni Smith
Layout and Design: Nina Danner
Copy Editor: Leah Rosasco

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