Dust Busters: How No-Plow Farmers Try to Save Our Soil
AbstractDo you have any great-grandparents who lived through the Great Depression in the United States during the 1930's? If so, they might have stories to tell about terrible dust storms that blackened the skies, from the Midwest to the east coast. Severe drought was a factor in causing this "Dust Bowl" era, but decades of poor farming practices contributed to it, too. In this environmental science fair project, you'll learn about farming methods that help keep dirt from drying up into dust, and help keep topsoil where it belongs—on the farm.
To determine whether no-till or plow-based farming methods are best at retaining surface moisture and preventing surface runoff.
Have you ever seen the extraordinary photographs of the "Dust Bowl" or the "Dirty Thirties"? Back in the 1930's, on the prairies of the United States and Canada, there were tremendous dust storms or "black blizzards" that turned day into night and reduced visibility to just a few feet. The storms were so enormous that at times they reached as far as the eastern coast of the United States, blackening the skies from Oklahoma, Texas, Colorado, and Kansas to Washington D.C. and New York City. In April 1935, the storms were so bad that many people thought the world was coming to an end.
Figure 1. This photo shows a dust storm from the 1930's. (NASA, April 18, 1935, Stratford, TX).
The Dust Bowl was an environmental catastrophe caused by two events:
- A severe drought brought on by cooler-than-normal tropical Pacific Ocean surface temperatures and warmer-than-normal tropical Atlantic Ocean surface temperatures.
- Decades of poor farming practices, like deep plowing and failure to rotate crops.
The great prairies of North America used to be covered by grasses, which helped hold moisture in the topsoil and helped keep topsoil in place. As settlers moved into the area though, they began farming the grasslands, using deep-plowing methods which killed the grasses in the topsoil. When the drought struck in the 1930's, there were few grasses to help control its damage. The topsoil dried up and turned to dust, which rose up into great dirt clouds anytime there were winds. Much of the rich, fertile topsoil of the North American plains, over 100 million acres, was wasted when it was blown away into the Atlantic Ocean. Consequently millions of acres of farmland were lost, forcing hundreds of thousands of people to flee to other states to try and survive. Their difficult lives were written about in John Steinbeck's famous novel, The Grapes of Wrath, which won both the Pulitzer Prize and the Nobel Prize for Literature.
While the Dust Bowl was an ecological and human tragedy on an enormous scale, farming practices around the world today continue to contribute to the loss of topsoil and degradation of farmlands in less dramatic, but just as troubling ways. One such common practice is called "turning the soil." This conventional tillage or plowing of the soil before planting seeds does the following:
- Aerates the soil,
- Warms the soil,
- Buries leftover crops,
- Buries animal waste, and
- Buries weeds.
The downside of plowing, though, is that it makes it much easier for wind and water, both forces of erosion, to wash or blow away the topsoil, which compromises food production. It also increases runoff of soil, fertilizer, and pesticides into waterways, increasing water pollution.
An alternative to plowing is no-till farming, where the soil is disturbed as little as possible. The soil is not turned over, and farmers leave leftover crops in the field after a harvest to act as a mulch, similar to how the grasses on the prairies of North America were used to hold moisture and topsoil in place, before farmland replaced them. Seeds are planted with special machinery that can push them down through the mulch into the undisturbed soil below.
Some of the advantages of no-till farming are that it:
- Reduces wind and water erosion of the topsoil.
- Reduces moisture loss from evaporation.
- Reduces water pollution caused by surface runoff.
- Requires less energy to prepare the fields (reduces the number of passes over the field).
- Requires 50–80 percent less fuel to work the fields.
- Requires 30–50 percent less labor.
- Does not kill earthworms in the soil.
- Increases the diversity of plants and animals.
- Increases the amount of carbon dioxide the field can remove from the atmosphere.
The United States leads other nations in adopting no-till farming methods, with 41 percent of its crops grown (as of 2004) with minimal disruption of the soil (Scientific American, 2008). With all its advantages, you might wonder why no-till farming has been slow to develop in other countries. There are several reasons. No-till farming requires:
- Specialized seeders (machines to plant seeds in undisturbed soil), which are expensive; some cost more than $100,000!
- Greater use of expensive fertilizers for the first few years, since the thicker surface layer of organic matter covering the farmland from leftover crops keeps nutrients, like nitrogen, from freely moving about. Crop rotation can help reduce the need for these extra fertilizers.
- Greater use of expensive herbicides to control weeds and pests, although crop rotation and organic farming methods can help reduce this.
- Lower harvest for some crops, like corn that is grown at far northern latitudes, because the soil is not warmed through tillage, so seeds sprout later.
- In developing countries, farmers use leftover crops as fuel, or to feed animals.
In this environmental science fair project, you'll see if no-till methods retain moisture and prevent surface runoff better than plow-based preparation of the soil. You'll first create models of a plowed field and a field prepared by no-till methods to see how each retains moisture. Then you'll build a surface runoff channel and fill it with different types of prepared soil to see which one best withstands water erosion.
Terms and Concepts
- Deep plowing
- Crop rotation
- Surface runoff
- What factors contributed to the Dust Bowl?
- What are the advantages and disadvantages of plow-based farming?
- What are the advantages and disadvantages of no-till farming?
This source shows photographs of dust storms from the Dust Bowl Era:
- (Tatarko, J). (n.d.). USDA-Agricultural Research Service Engineering and Wind Erosion Research Unit Wind Erosion: Problem, Processes, and Control. Retrieved March 9, 2007.
This source explains the ocean conditions that led to the drought during the Dust Bowl:
- NASA. (2004, March 18). NASA Explains "Dust Bowl" Drought. Retrieved April 22, 2009.
These sources compare no-till and plow-based farming methods:
- Huggins, D. R. and Reganold, J. P. (2008, July). No-Till: How Farmers are Saving the Soil by Parking Their Plows. Retrieved April 24, 2009.
- Monsanto. (2009). Healthy Soils for a Better Planet. Retrieved July 5, 2018.
For help creating bar charts, try this website:
- National Center for Education Statistics (n.d.). Create a Graph. Retrieved March 19, 2009.
Materials and Equipment
Note: Because this science fair project uses a lot of dirt and water, you will need to ask your parents for a good outdoor test area, one that can easily be washed down after you are done testing. You will also need to wear clothing that you don't mind getting dirty.
- Soil moisture meter; available at some hardware and garden stores, and from online sellers, like www.amazon.com.
- Plastic box, like a kitty litter tray, approximately 14x17x5 inches; available at pet stores
- Soil; can be potting soil, dirt from the ground, or a mix of the two (need approximately 2–3 large buckets full of soil)
- Liquid measuring cups, 4-cup size or larger, (2). The read-from-above types are easiest to use; available from your local home goods store.
- Mulch, such as straw, dead plant matter, or grass clippings (3–4 large handfuls)
- Hand trowel; available at garden or hardware stores
- Adjust-A-SpoutTM downspout extender or approximately 4–6 feet of a rain gutter; both available at hardware stores or online
- Dry measuring cup, 1-cup size
- Sturdy box or stool
- Permanent marker
- Lab notebook
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Preparing Your Field Models
- Fill the plastic tray evenly with soil until it is about one-half to two-thirds full.
- Press down firmly on the soil with your hands or feet, so that is compacted.
- Fill one of the liquid measuring cups with about 3–4 cups of water.
- Slowly pour about 2 cups of water evenly over the compacted soil.
- Press down firmly on the soil and wait a minute or two.
- Press the probe of the soil moisture meter all the way down to the bottom of the soil in the top left corner of the tray. Observe the moisture reading. If it is less than about "8" (on a scale of 1 to 10), then remove the probe and add a little more water, approximately 1/4 cup, to that corner. Press down firmly on the soil and wait a minute or two. It doesn't have to be exactly "8"—a measurement that is a little more or a little less than an "8" is okay.
- Repeat step 6 until all areas of the tray are around an "8" on the moisture meter.
- Wipe the probe clean on a soft, dry cloth.
- Press down firmly on all the soil one last time.
- Using the hand trowel, turn over the soil in one-half of the tray. Be sure to dig all the way to the bottom of the tray as you turn it over. Turning over the soil with the hand trowel will imitate plowing of the soil. This half of the tray will be your model of a plowed field.
- Do not turn over the soil in the other half of the tray. Instead keep the soil compacted and cover it with a thin layer of mulch, or dead plant matter. This half of the tray will be your model of a no-till field.
- Place your tray in a warm, sunny area and immediately begin testing.
Testing Your Field Models
- Insert the probe of the moisture meter into the plowed field soil, until it touches the bottom of the tray. See Figure 2. Do this in the top, middle, and bottom of the plowed field model.
Figure 2. This photo shows the moisture meter probe inserted into the middle of the plowed field model.
- Record your measurements in a data table, like the one below. These will be your initial measurement for time equal to "0."
|Moisture Meter Readings for Plowed Field Model|
- Repeat steps 1–2 for the no-till field model.
- Repeat steps 1–3 every hour for the next 5 hours.
Analyzing Your Moisture Meter Readings
- For each time in each data table, calculate the average moisture meter reading.
- Plot the time on the x-axis and the average moisture meter reading on the y-axis for each field model. You can make the line graph by hand or use a website like Create a Graph to make the graph on the computer and print it. Which field model retained moisture the best?
Preparing Your Surface Runoff Model
Note: The soil in this model should be dry. If your soil is not dry, then spread it out for a day on a large plastic garbage bag.
- Place the downspout extender (gutter) on the ground. Do not extend it to its full length, but keep it at its shorter length. Sprinkle 4 cups of fresh, dry soil, evenly over the bottom of the gutter. Press down on the soil with your foot, so that the soil is firmly compacted.
- Place the swivel end of the extender on the box or stepping stool, and the other end of the extender on one of the liquid measuring cups. The swivel end of the extender should be several inches higher than the end resting on the measuring cup. Mark the point at which the swivel end meets the box or stepping stool with a permanent marker, so that you know how to set up the extender on repeat trials.
- Measure out 3 1/2 cups of water into the other liquid measuring cup.
- Pour the water all at once into the swivel end of the extender.
- Wait about 1–2 minutes to allow the water to completely drain out of the gutter. The exact time you wait is not critical. Just make sure you wait the same amount of time for each trial in the experiment. Record in your lab notebook about how much time you waited so you will remember for each trial.
- Measure the runoff water level in the liquid measuring cup at the end of the extender. Record your measurement in a data table.
- Dump and rinse out the measuring cup.
- Rinse off the gutter.
- Repeat steps 1–8 two more times, so that you have a total of three trials, using compacted dirt in the gutter. By repeating the experiment three times, you'll make sure your results are accurate and repeatable. These will be the trials for your no-till farming model.
- Repeat steps 1–9 three times using 4 cups of dirt that has just been loosely and evenly sprinkled into the gutter, and not compacted. These will be the trials for your plow-based farming model.
Figure 3. This photo shows the downspout extender set up for testing with the plow-based farming model.
Analyzing Your Runoff Water Data Tables
- Average your runoff water level readings for the compacted dirt (no-till field) and the loosely sprinkled dirt (plowed field). Using graph paper or a website like Create a Graph, make a bar chart showing the field types on the x-axis and runoff water level readings on the y-axis. Which type of field produced less surface runoff?
Ask an Expert
- Investigate how moisture content of the soil affects surface runoff by using the surface runoff model. Keep the soil compact for all trials, but vary and measure the soil's moisture content to see how much this affects surface runoff.
- Does plowing affect the amount of soil erosion after a rainstorm? Find out by devising a way to adapt the surface runoff model (above) to also measure the amount of soil that washes away.
- This Science Buddies project, Riprap: It's Not Hip Hop But Erosion Stop, explores how rocks can control water erosion.
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