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• Measuring Plant Growth

Project Summary

Difficulty	6
Time required	Very Long (several weeks to months)
Prerequisites	None
Material Availability	Specialty items (can easily be purchased online through Carolina Biological Supply Company)
Cost	Average ($50 - $100)
Safety	Requires adult supervision during use of nitrogen fertilizer

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Sponsor

Sponsored by a generous grant from Monsanto Fund

Objective

The goal of this experiment is to compare the effects of added nitrogen fertilizer vs. nitrogen-fixing bacteria on the growth of clover.

Introduction

Plants require more than just water and sunlight to grow. They also require many nutrients found in the soil. One of the most important nutrients required for plant growth is nitrogen. Nitrogen is used to build plant proteins and nucleic acids, including DNA.

Nitrogen is found naturally in the atmosphere and in the soil. Even though there is an abundance of nitrogen available, the most common form of nitrogen (N₂) cannot be used by plants. Nitrogen can be combined chemically with oxygen or hydrogen to form types of nitrogen compounds that plants can use. These nitrogen compounds can be added to the soil in the form of ammonium (NH₄⁺) and nitrate (NO₃⁺) fertilizer. Plants grow well when fertilizer containing nitrogen is added to the soil, but this method can be expensive and has to be repeated each time the nitrogen in the soil is used up.

Bacteria to the rescue! Bacteria are small, single-celled organisms that live in nearly every environment on Earth. From Antarctica to the hot springs in Yellowstone National Park, some of these organisms are able to live in extreme environments and have many amazing capabilities. Some species of bacteria are able to turn milk into cheese while others can reproduce in less than twenty-four hours. Rhizobium leguminosarum, the bacteria that you will study in this experiment, can turn the nitrogen in the soil into usable nitrogen compounds like ammonium and nitrate ions. These bacteria can attach themselves to the roots of some plants, forming little growths called nodules. The bacteria receive nutrients and protection from the plant roots and the plants get their fill of nitrogen. Both organisms benefit from this symbiotic relationship. Legumes, and clover in particular, readily form this symbiotic relationship with bacteria.

In this experiment, you will grow clover plants in soil with no nitrogen added, in soil with nitrogen fertilizer added, and in soil containing nitrogen-fixing bacteria. You will monitor the nitrogen levels in each type of soil using a nitrogen testing kit. You will observe the effects of nitrogen on the health of the clover plants by measuring the increase in biomass of each plant during the experiment.

Terms, Concepts and Questions to Start Background Research

• legume
• macronutrient
• micronutrient
• nitrogen-fixation
• nodule
• symbiosis

Questions

• What nutrients do plants need to survive?
• How do nitrogen-fixing bacteria change nitrogen into ammonium and nitrate ions?
• What is symbiosis and what types of organisms form symbiotic relationships?
• What types of plants form symbiotic relationships with nitrogen-fixing bacteria?
• How do root nodules form?

Bibliography

• Excellent Pictures and Diagrams of Root Nodules:
  Legume Root Symbiosis
  http://www.botany.hawaii.edu/faculty/webb/BOT410/Roots/RootSymbioses.htm
• Chemical Information on the Nitrogen Cycle and Nitrogen-fixation:
  The Microbial World: The Nitrogen cycle and Nitrogen-fixation
  http://helios.bto.ed.ac.uk/bto/microbes/nitrogen.htm
• Information on Symbiosis and Nitrogen-fixation:
  http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/N/NitrogenFixation.html
• Buy Supplies Online:
  Carolina Biological Supply Company
  http://www.carolina.com/

Materials and Equipment

Note: Adult supervision required during use of nitrogen fertilizer.

• at least nine small pots
• potting soil
• one packet of clover seeds
• one packet of Rhizobium leguminosarum Inoculum with Clover Seeds (available from Carolina Biological Supply Company)
• nitrogen fertilizer
• one Rapitest Soil Test Kit (available from Carolina Biological Supply Company)
• metric scale
• beaker

Experimental Procedure

Note: Adult supervision required during use of nitrogen fertilizer.

1. Make sure pots have holes in the bottom to allow the roots to "breathe."
2. Measure equal amounts of soil into each of the pots.
3. Moisten the soil in each pot with the equal amounts of water.
4. Label three pots "no nitrogen added," three pots "nitrogen fertilizer," and three pots "nitrogen-fixing bacteria."
5. Plant seeds in each pot according to seed packet instructions. In the pots labeled "no nitrogen added" and "nitrogen fertilizer" plant seed from the regular clover packet. In the pots labeled "nitrogen-fixing bacteria" plant the Rhizobium leguminosarum-inoculated clover seeds.
6. Place plants near a sunny window or under a grow light.
7. Set a schedule for watering. Soil should be kept moist.
8. Water the "no nitrogen added" and "nitrogen-fixing bacteria" pots with regular water. Water the "nitrogen fertilizer" pots with water and nitrogen fertilizer at the brand of fertilizer's recommended concentration. You may not need to add fertilizer at each watering.
9. Clover will grow to maturity in 5–6 weeks. When clover plants are mature, proceed with experiment.
10. Use the Rapitest Soil Test Kit to measure the amount of nitrogen in the soil of each pot. Remember to record your data in your lab notebook.
11. After these measurements are complete, carefully remove each plant from the soil and shake off any excess soil from the roots.
12. Measure the total biomass of each plant and record data in your lab notebook. For more information on scientifically measuring plant growth see the Science Buddies How-to page, Measuring Plant Growth.
13. Compare the average nitrogen levels in each type of soil and the average biomass of the clover grown in each type of soil. Which type of soil had the highest levels of nitrogen? Which type of soil produced the greatest biomass of clover? Was there any noticeable difference in the health or appearance of the clover grown in the different soils?

Variations

• Compare different amounts of nitrogen fertilizer to the clover inoculated with the nitrogen-fixing bacteria.
• Test the abilities of other plants to form a symbiotic relationship with nitrogen-fixing bacteria.
• Test different species of nitrogen-fixing bacteria to see which type produces the most nitrogen in the soil or the healthiest plants.

• For more science project ideas in this area of science, see Plant Biology Project Ideas.

Credits

La Né Powers

Last edit date: 2007-03-22 22:00:00