Target Grade Level / Age Range:

Grades 9-12


30 minutes on day 1, two or more weeks grow time, 50 minutes on day 2


Students will understand how buffer zones at the edges of fields can protect waterways by slowing the movement of water and minimizing soil runoff.


  • 2 or more: 13” x 9” inch aluminum baking pans
  • Grass seeds (lawn grass seeds will work fine and establish quickly, but for a more authentic experiment try to find a native prairie grass mix and allow for a longer growing time.)
  • Soil – enough to fill each pan 2-3 inches deep. (Potting soil will work fine, but for a more authentic experiment try to get local soil from a field that is a silt/clay mix.)
  • Nitrate and nitrite test strips (i.e.
  • Phosphate test strips (i.e.
  • N-P-K fertilizer (MiracleGro or a similar house plant fertilizer will work fine, but for a more authentic experiment consult an agronomist or co-op dealer to determine a fertilizer mix rate that a farmer might actually apply to their crop.
  • Gravel or pebbles
  • Cling film or plastic cover
  • Plastic cups

Suggested Companion Resources (books and websites)

Vocabulary (with definitions)

  • Saturated Buffer: allow nutrients to be removed by redistributing tile water into the riparian buffer soil profile before reaching the stream
  • Prairie Strips: Buffer strips of native prairie grasses placed on the contour in crop fields, combined with filter strips of prairie grass strategically placed where runoff leaves the field.
  • Stream Buffers: Buffers are grassy or native vegetation adjacent to streams that trap sediment from surface runoff.
  • Grassed Waterway: Areas within fields that are maintained in grass to address areas of concentrated water flow.
  • Conservation Reserve Program: The Conservation Reserve Program (CRP) pays a yearly rental payment in exchange for farmers removing environmentally sensitive land from agricultural production and planting species that will improve environmental quality.

Background – Agricultural Connections (what would a teacher need to know to be able to teach this content)

Buffers zones are important for good water quality. Buffer zones help to prevent sediment, nitrogen, phosphorus, pesticides and other pollutants from reaching a stream. Buffer zones are most effective at improving water quality when they include a native grass or herbaceous filter strip along with deep rooted trees and shrubs along the stream.

Riparian vegetation is a major source of energy and nutrients for stream communities. They are especially important in small, headwater streams where up to 99% of the energy input may be from woody debris and leaf litter. Overhanging riparian vegetation keeps streams cool. Riparian buffers provide valuable habitat for wildlife. In addition to providing food and cover they are an important corridor or travel way for a variety of wildlife. Forested streamsides benefit game species such as deer, rabbit, pheasant and nongame species like migratory songbirds. Riparian vegetation slows floodwaters, thereby helping to maintain stable streambanks and protect downstream property. By slowing down floodwaters and rainwater runoff, the riparian vegetation allows water to soak into the ground and recharge groundwater. Slowing floodwaters allows the riparian zone to function as a site of sediment deposition, trapping sediments that build stream banks and would otherwise degrade streams and rivers.

Interest Approach or Motivator

Explain to students that they will be setting up an experiment to determine if and to what extent grassed waterways might reduce nitrates and/or phosphates in runoff water from a field. You can do one set of pans as a display experiment for the entire class to observe. Or if supplies allow, break the class into multiple small groups and allow each group to conduct the experiment.

Pass out two pans to each group. One pan will serve as a control with no grass planted. One will serve as the trial with grass planted. Line the base of each pan with the gravel or pebbles. This will help keep the soil drained and from getting too wet. Line each baking tray with 2-3” of soil. Evenly spread the grass seeds across the top of one of the trays. Sprinkle a little more soil on top of the seeds (1/4” or less) so that they are covered but no planted too deeply.

Use one of the following fertilizer application rate calculations to determine how much fertilizer should be applied based on the N-P-K mix that you are using. HINT: an acre is 43,560 sq. ft. a 13” x 9” pan is .81 sq. ft. If you calculate fertilizer application rate per acre, then multiple by a factor of .0000186 (.81/43560) to determine how much fertilizer to add to your pan.

Apply the fertilizer evenly to both pans. Water both pans. Soil should be moist but not soggy. Apply water gently so as not to disrupt the seeds or soil planted. Both pans can be covered with cling film or a plastic cover to hold in the moisture until the seeds are germinated (2-5 days). Then remove the cover. Place pans in an area that is room temperature or slightly warmer. Pans should receive sufficient light (natural light if possible). Monitor the pans over the course of two or more weeks. Water as needed. The soil should stay slightly damp, but be careful not to over water as there isn’t sufficient drainage in the pans. After two weeks, you should have a healthy stand of grass in one pan.


  1. After two or more weeks, bring out the experiment pans. Set both pans on a flat surface. Raise one end of each pan 1-2” and place a block under it so that each pan is on a slight angle. The lower edge of the pans should be hanging slightly over the edge of the table. Be sure to stabilize the pans so that they don’t slide off the table.
  2. Poke a small hole at the base of the lower side of the pan so that water can drain to the hole. Gently water each pan and hold a cup below the hole to catch water that has been filtered through the soil and drained out of the pan. Have students label the cups control (bare soil, no grass) and grassed waterway.
  3. Have students record their visual observations of the process. Which pan drained more quickly? Is there any difference in water color? In water clarity?
  4. Follow the instructions on the nitrate and phosphate test kits to test each water sample. Have students record their findings. If there are multiple groups, record all measurements on a board or flip chart. Students can later compare and graph their results.
  5. What were the results? Which water sample contained higher amounts of nitrates and/or phosphates? Why?
  6. Teach content in accompanying PowerPoint slides 2-9 and have students capture important information into their notebooks.
    1. Saturated Buffer: allow nutrients to be removed by redistributing tile water into the riparian buffer soil profile before reaching the stream
      1. Water level control structure is installed near the outlet of a tile line, within or immediately adjacent to an existing stream buffer.
      2. A portion of the water is diverted into a tile line parallel to the stream and within the buffer.
      3. Excess nitrate in the tile flow is converted to harmless nitrogen gas in the soil of the stream buffer due to organic matter and low oxygen.
      4. Advantages include:
      5. low maintenance,
      6. simple to install
      7. reasonable cost.
      8. Challenges include:
      9. site specific soil investigations are required;
      10. interim practice standard complicates within CRP areas;
      11. very few people have experience with site assessment, design, and installation;
      12. a buffer of perennial vegetation is needed.
      13. must assure impacts of impeded drainage on the cropland upstream are minimal and that streambank soils will remain stable with prolonged saturation.
    2. Prairie Strips: Buffer strips of native prairie grasses placed on the contour in crop fields, combined with filter strips of prairie grass strategically placed where runoff leaves the field.
      1. Prairie Strips: results in large improvements in runoff water quality with only a small (~10%) portion of the field taken out of row crop production.
      2. Iowa State University data has shown that returning only a small fraction of cropland to deep rooted, native prairie plants with stiff, upright stems can dramatically reduce soil erosion by 95%,
      3. Reduces losses of nitrogen by 85% and phosphorus by 90% in surface runoff.
      4. Stiff-stemmed native grasses provide greater water quality benefits than non-native grasses like smooth bromegrass because the native grasses are much less likely to lay flat when there is runoff.
      5. Small prairie areas can provide important habitat for pollinators and at-risk species.
      6. No negative impacts on crop yield.
      7. Can potentially be enrolled in programs such as CRP to receive rental payments and to help with the cost of the seed mixes.
    3. Stream Buffers: Buffers are grassy or native vegetation adjacent to streams that trap sediment from surface runoff.
      1. Stream buffers:
      2. reduce phosphorus entering a waterway,
      3. filter nitrogen as it moves in groundwater through the soil,
      4. stabilize stream banks and provides habitat for wildlife.
      5. AKA: riparian buffer strips and filter strips.
      6. Areas surrounding water sources that have been taken out of agricultural production.
      7. Planted with a variety of grasses, shrubs and/or trees that help improve water quality.
      8. Primary benefit: trap soil and phosphorus in surface runoff before it reaches a stream or river.
      9. Soil erosion must be well controlled on the land draining toward the stream buffer.
      10. Uniform buffer is preferred by many producers for ease of installation
      11. Varying the width of the stream buffer based on the amount of runoff that enters each section is more effective.
    4. Grassed Waterway: Areas within fields that are maintained in grass to address areas of concentrated water flow.

Essential Files (maps, charts, pictures, or documents)

Did you know? (Ag facts)

  • Buffer zones can provide important habitat for pollinators, birds, mammals and at-risk species.

Extension Activities (how students can carry this beyond the classroom)

  • Using the data collected from the initial experiment, have students graph the data. How does this data support show how biodiversity of plant species might be maintained in ecosystems by utilizing grassed waterways or other buffer zones of different scales?
  • Present students with pictures of a local field or if possible take a field trip to a local field. Have students design, evaluate, or refine a buffer zone based on that specific field. Have students sketch out their solutions and provide explanation to their recommendations.


Lesson plan development was funded by the Resource Enhancement and Protection Conservation Education Program (REAP CEP). Resource Enhancement and Protection Program (REAP): Invest in Iowa our outdoors, our heritage, our people. REAP is supported by the state of Iowa, providing funding to public and private partners for natural and cultural resources projects, including water quality, wildlife habitat, soil conservation, parks, trails, historic preservation and more.


Will Fett

Organization Affiliation

Iowa Agriculture Literacy Foundation

National Agriculture Literacy Outcomes

  • T1.9-12.c. Discuss the scientific basis for regulating the movement of plants and animals worldwide to control for the spread of potentially harmful organisms (e.g., invasive species and disease causing organisms such as foot and mouth disease and avian and swine flu) as well as the methods of control in place (state, national, and international policies, economic incentives)
  • T1.9-12.a. Describe how wildlife habitats are created and maintained by farmers/ranchers and why these habitats are important (e.g., promoting pollinator habitat, insect refuges, creating buffer zones for nutrient management, etc.)
  • T1.9-12.b. Describe resource and conservation management practices used in agricultural systems (e.g., riparian management, rotational grazing, no till farming, crop and variety selection, wildlife management, timber harvesting techniques)

Iowa Core Standards

  • HS-LS2-2. Use mathematical representations to support and revise explanations based on evidence about factors affecting biodiversity and populations in ecosystems of different scales. (riparian areas / buffer zones)
  • HS-LS2-7. Design, evaluate, and refine a solution for reducing the impacts of human activities on the environment and biodiversity. * (no-till, buffer zones, riparian area management, bioreactors)
  • HS-LS4-6. Create or revise a simulation to test a solution to mitigate adverse impacts of human activity on biodiversity. * (buffer strips, riparian area management)
  • HS-ESS3-4. Evaluate or refine a technological solution that reduces impacts of human activities on natural systems. * (bioreactors, buffer strips, terraces, cover crops)

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