Do grass roots stop soil washing away?
- 🌳 Outside
- 🧼 Wash your hands after
- 🧽 A bit messy
My hypothesis
If I change what covers the soil, then how deep the washed-away mud is in the cup after 15 minutes will ______, because ______.
You fill in the blanks. Think about what roots do underground, and what leaves do when water hits them. A guess is a good because: the test finds out.
Change, measure, keep the same
CHANGE
what covers the soil: Bare soil, Grass grown for two weeks, A cover of dry leaves
MEASURE
how deep the washed-away mud is in the cup after 15 minutes, in mm
KEEP THE SAME
- the same garden soil, patted down the same way
- the same slope for every plate
- one cup of water poured at the same speed, in the same place
- all nine plates watered the same each day
Scientists call the thing you change the independent variable and the thing you measure the dependent variable. The things you keep the same are the controls: if one of them changed too, you wouldn't know which change made the difference. Try each of the 3 levels 3 times.
What you need
- Paper plates: 9 sturdy ones, all the same
- Soil dug from the garden or yard: 9 cups
- Grass seed
- Measuring spoons
- Water from the tap
- A spoon
- A leafy bush or tree outside, or a big potted plant: for a handful of dry fallen leaves
- Flat cardboard: a flat piece, about 40 cm
- Some books: 2
- Masking tape, to mark lines
- A big bowl: a big one
- A measuring cup
- Clear plastic cups, all the same size: 9 tall ones
- 📏 A ruler
Steps
- Fill nine paper plates with garden soil right up to the rim, and pat it flat with a spoon.
- Sprinkle a teaspoon of grass seed over three of the plates and press it in gently.
- Stand all nine plates in one bright, sheltered spot, on trays or plastic bags to catch the drips.
- Every day for fourteen days, give each plate two tablespoons of water.
- On day fourteen, lay one flat layer of dry leaves over three of the bare plates.
- Work outside or at the sink: prop one end of the cardboard on two books, its other end at a table's edge.
- Tape a plate to the low end so that its edge hangs over a big bowl.
- Pour one cup of water slowly onto the top of the soil while you count to ten.
- Pour the muddy water into a tall clear cup, and label it grass, leaves or bare.
- Test all nine plates the same way, mixing up the order of the three kinds.
- Leave the cups still for 15 minutes, then stand a ruler against each and measure the mud in mm.
- Muddy water is never for drinking: pour it onto the garden when you've finished.
- Find the mean mud depth for each cover and draw a bar graph.
- Wash your hands after touching the soil.
Every step is one you can do yourself, with a grown-up nearby. Write each number down straight away, in the table below, so nothing is lost.
Your results table
Name ______________________ Fair day ____________
Question: Do grass roots stop soil washing away?
I changed: Soil cover I measured: how deep the washed-away mud is in the cup after 15 minutes (mm)
| Soil cover | Try 1 (mm) | Try 2 (mm) | Try 3 (mm) | Mean |
|---|---|---|---|---|
| Bare soil | ||||
| Grass grown for two weeks | ||||
| A cover of dry leaves |
MY GRAPH (a bar graph: soil cover along the bottom, mm up the side)
What I noticed: ______________________________________________
From 4th grade, add the tries for each level and divide by how many there were: that's the mean, and it goes in the last column. Then draw a bar graph, one bar for each thing you tried.
Name ______________________ Fair day ____________
Question: Do grass roots stop soil washing away?
If I change what covers the soil, then how deep the washed-away mud is in the cup after 15 minutes will ________________, because _____________________________________________
| I CHANGE | I MEASURE | I KEEP THE SAME |
|---|---|---|
| Soil cover: Bare soil, Grass grown for two weeks, A cover of dry leaves | how deep the washed-away mud is in the cup after 15 minutes (mm) |
|
What I think will happen, in my own words:
Name ______________________ Fair day ____________
Question: Do grass roots stop soil washing away?
| Date | What I did | What I saw | What I think |
|---|---|---|---|
Name ______________________ Fair day ____________
Question: Do grass roots stop soil washing away?
| Date | What I did | What I saw | What I think |
|---|---|---|---|
Name ______________________ Fair day ____________
Question: Do grass roots stop soil washing away?
| Date | What I did | What I saw | What I think |
|---|---|---|---|
Name ______________________ Fair day ____________
Question: Do grass roots stop soil washing away?
My hypothesis was ☐ right ☐ partly right ☐ not right.
I know because my numbers show:
What surprised me, or what might have gone wrong (7th and up):
Next time I would test:
Idea: Change a second thing: let the grass grow for 7, 14 and 21 days before you test it, and graph the mud depth against the days.
Why it works
Roots grow through the soil and hold it together like a net, so water can't lift the soil grains away so easily. Grass blades also slow the water down and soften the blow of the drops. A cover of leaves shields the soil in a similar way, so bare soil usually loses the most.
Going further (7th and up): Change a second thing: let the grass grow for 7, 14 and 21 days before you test it, and graph the mud depth against the days.
Board layout
- ❓ Question (10 × 8 in): Do grass roots stop soil washing away?
- 💭 Hypothesis (10 × 9 in): If I change what covers the soil, then how deep the washed-away mud is in the cup after 15 minutes will ______, because ______.
- 🧺 Materials (10 × 12 in): 13 things: see your list.
- 🪜 Steps (22 × 9 in): 14 steps, three tries at each level.
- 📊 Results (22 × 16 in): Your table (Soil cover down the side, tries across) and your bar graph.
- ✅ Conclusion (10 × 14 in): My hypothesis was right / partly right / not right. I know because…
Materials to list: Paper plates; Soil dug from the garden or yard; Grass seed; Measuring spoons; Water from the tap; A spoon; A leafy bush or tree outside, or a big potted plant; Flat cardboard; Some books; Masking tape, to mark lines; A big bowl; A measuring cup; Clear plastic cups, all the same size.
Bring photos or drawings of your test. Nothing wet, hot, powered or alive on the table.
This project at your grade
| 4th–6th grade | Tries: three at each level. The table: units in the header and a mean column. The graph: a bar graph, or a line for a number that grows. The conclusion: right, partly or not, and the numbers that show it. |
|---|---|
| 7th grade and up | Tries: three or more at each level. The table: a mean for every level of both tests. The graph: a graph with two lines or two sets of bars. The conclusion: the numbers, what might have gone wrong, and a next question. Second variable: let the grass grow for 7, 14 and 21 days before you test it, and graph the mud depth against the days. |
Every grade this project fits works out a mean. See every project for 4th grade, or print a blank results table.
What a judge will ask
- What did you change, and what did you measure? I changed what covers the soil and measured how deep the washed-away mud is in the cup after 15 minutes, in mm.
- What did you keep the same, and why does that matter? I kept the same garden soil, patted down the same way and the same slope for every plate the same, so the only difference was what covers the soil.
- How many times did you test it? 3 times at each of my 3 levels.
- If you did it again, what would you change or test next? I'd let the grass grow for 7, 14 and 21 days before you test it, and graph the mud depth against the days.
Make it yours
Keep this project on this device and Peabody counts down to your fair day, with a plan for each day. Nothing is sent anywhere.
Try next
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