Loosin' It A study of the effects of soil type and plant growth on nitrogen leaching Overview This activity is designed to explore how nitrogen can leach through soil and into groundwater. Students will experiment with variables such as soil type and the presence or absence of plants to determine their effects on the leaching of nitrogen applied as a liquid fertilizer. Students construct a leaching column using plants and soil and measure the levels of nitrogen leaching through the columns. Biology and agriculture concepts Soil ecology Nitrogen cycle Plant growth and development Water testing Leaching 11-1 I Leaching
The Teachable Moment Background The biology teacher could use this unit when teaching plant growth and development, ecology, environmental science, soil science or the nitrogen cycle. The agriculture teacher could use this unit when studying plant growth and development, soil science, fertilizer application, water testing, and leaching. Water is a versatile solvent. Many soil-borne materials dissolve easily in it. As water percolates through soil, many materials such as minerals, applied fertilizers, herbicides, pesticides, and other pollutants dissolve and move with the water. This movement of nutritive or harmful elements through soil by percolation is called leaching. Leaching may be detrimental to plants because it moves necessary materials out of the root zone into deeper levels of the soil. Dissolved minerals are then no longer available for use by the plant. On the other hand, leaching may be beneficial to plants when it moves harmful salts and other pollutants deep into the soil and away from plants. Leaching is also significant in that it moves materials from the soil into the groundwater below causing groundwater contamination. This lab investigates the effects of soil type and plant growth on nitrogen leaching. Students will compare an artificial soil mix to a local topsoil. Wisconsin Fast Plants are used to assess the effects of plant growth on leaching. There are many factors which affect leachingsoil depth, soil texture, plant type and density of plant growth are a few. Teacher Management Preparation Collecting and sterilizing topsoil should take about 1 hour. Activity time Constructing the TerrAqua Columns and setting up the experiment will take about 1 class period. On day 7, applying fertilizer will take about 10 minutes. Performing the nitrate test upon termination of the experiment takes about 1 class period. Water levels in the reservoirs must be checked periodically. 11-2 I Leaching
Materials One 1-liter delabelled bottle/student Liquid fertilizer (20-20-20 N-P-K) Light banks with minimum of 6 fluorescent lights Wicks For each group of 4 students: razor blade scissors grease pencil or marker hole punch or poke 1:1 Jiffy to local sterilized topsoil mix* Sterile soil* Jiffy Mix* Fast Plant seed (10-20 seeds/ student) LaMotte soil kit (enough for 1 test/ student) Materials for ten-fold dilution of 10 mls of leachate. *You will need approximately: 100 mls of sterile local soil/student 250 mls of Jiffy Mix/ student. With this make up the 1:1local soil: Jiffy Mix mixture. You will need app. 150 mls of this mixture/ student. The remaining Jiffy Mix will be used for the all Jiffy Mix columns. Sources of materials Carolina Biological Supply for Fast Plants. Local garden center for fertilizer and Jiffy Mix soil. Tips 1. Water gently as not to create depressions in the soil. 2. Procedure for nitrogen testing is included in Appendix C. 3. The experiment may be changed to allow some flexibility in the length and complexity of the activity such as measuring the nitrate levels at different intervals during the course of the plant development. Key Terms Leaching: the process of extracting nutritive or harmful elements from soil by percolation. Percolation: the process by which materials (liquid, powder, or small particles) may pass through a porous substance or small holes. 11-3 I Leaching
References Forth, Henry D. Fundamentals of Soil Science, John Wiley & Sons Publishing New York, 1990 8th Edition ISBN- 0-0471-52279-1 Singer, Michael J, Munns, Donald N. Soils An Introduction, MacMillan Publishing Company, New York, 1987 ISBN 0-02-410860 Jarman, Maggie, Ground Water- Practical Ways of Learning About Soils -Field Studies Council for Leiceshtershire Museums, Art Galleries and Record Service Toward A Sustainable Agriculture, Center For Integrated Agriculture Systems School of Natural Resources College of Agriculture & Life Sciences, University of Wisconsin-Madison, Mt. Horeb, Wisconsin, 1991 11-4 1 Leaching
Student materials Loosin' It A study of the effects of soil type and plant growth on nitrogen leaching Introduction Water is a versatile solvent. Many soil-borne materials dissolve easily in it. As water percolates through soil, many materials such as minerals, applied fertilizers, herbicides, pesticides, and other pollutants dissolve and move with the water. This movement of nutritive or harmful elements through soil by percolation is called leaching. Leaching may be detrimental to plants because it moves necessary materials out of the root zone into deeper levels of the soil. Dissolved minerals are then no longer available for use by the plant. On the other hand, leaching may be beneficial to plants when it moves harmful salts and other pollutants deep into the soil and away from plants. Leaching is also significant in that it moves materials from the soil into the groundwater below causing groundwater contamination. This lab investigates the effects of soil type and plant growth on nitrogen leaching. Students will compare an artificial soil mix to a local topsoil. Wisconsin Fast Plants are used to assess the effects of plant growth on leaching. There are many factors which affect leachingsoil depth, soil texture, plant type, and density of plant growth are a few. This lab investigates the effects of soil type and plant presence or absence on nitrogen leaching. An artificial soil mix (Jiffy Mix) is compared to local topsoil. Wisconsin Fast Plants are used to assess the effects of pla~t growth on leaching. There are many factors which affect leaching-soil depth, soil texture, plant type and density of plant growth are a few. Leaching 1 11-5
Procedure 1. In groups of four, prepare four TerrAqua Columns as described in the manual's Bottle Biology Introduction. 2. Collect some local soil. To kill any plant disease organisms that may be in the soil, microwave 2-cup portions of the soil for 30 seconds on high. 2. To the inverted top of two of the bottles add about 250 mls of Jiffy Mix soil (enough to fill the top section to within 1 I 4 inch of the top). Label one bottle A and the other B. 3. To the inverted top of the other two bottles add 300 mls of a 1:1 ratio of Jiffy soil: local topsoil mix. (Tips-- If soil is lumpy, screen it or break up larger chunks. Also, mix 3 tablespoons of water with the Jiffy mix.) Add the same volume as was added to Columns A and B. Label one bottle C and the other D. 5. To bottles A and C, add 20-40 Fast Plant seeds each. With your finger, push each seed into the soil about 1 I 4 inch. If necessary, cover each with a small amount of soil of the proper type. 6. Gently add enough water to the soil in each bottle so that a small amount of water drips through the wick into the chamber below. 7. Fill the reservoir with water. 8. Add 10 ml of fertilizer solution to the soil in each bottle seven days after planting. 9. When the plants reach flower bud stage, cut the wick at the base of the upper bottle. Flush the column with water until it begins to drip through. Collect the first 10 mls of leachate that drip through. Do this to each of the bottles collecting the leachate separately 10. Test the leachates using the LaMotte kit and protocol described in Appendix C. Record nitrate level. 11-6 I Leaching
Data Sheets Preparation Date Planted, Date Fertilized. Amount of fertilizer -------- Observations:. Nitrate Levels in Leachate Date of Collection Column #1 (Plants, All Jiffy) Column #2 (No Plants, All Jiffy) Column #3 (Plants, Topsoil and Jiffy) Column #4 (No Plants, Topsoil and Jiffy) Observations:, Leaching 1 11-7
Results and discussion Experimental Set-Up 1. Two different variables are being tested in this experiment. What are they? Effects of Soil 1. If plants are present, how do the nitrate levels in the leachate from the Jiffy and topsoil compare? 2. If plants are absent, how do the nitrate levels in the leachate from the Jiffy and topsoil compare? Effects of Plant Growth 1. Given Jiffy Mix as the planting medium, how do the nitrate levels in the leachate with and without plants compare? 2. Given topsoil as the planting medium, how do the nitrate levels in the leachate with and without plants compare? Overall Results 1. Can you draw any conclusions or hypotheses about the interaction of plant growth and soil type? 2. How might results be different if you used a clay soil vs a sandy soil? Extensions What would happen when the soil columns are of different lengths? What would happen if you did not provided a wick system between the reservoir and the soil? What would happen when different concentrations of nitrogen are added? What would happen when various types of fertilizers are intro duced? (Organic, slurry, liquid, dry) What would happen if pollutants are introduced? (i.e. salt intrusion) What would happen when application times are varied? 11-8 I Leaching
What would happen if the plant density were altered? What would happen if you varied the type of plant? What would be the effect of a plant with fibrous roots on the leaching of soil in comparison with a plant with tap root system? How would varying the temperatures effect what is leached? How would varying the photoperiods on the plants affect what is leached? 11-9 I Leaching