Grade by Grade
E. Earth and Space Systems · Soils in the Environment

What Gets Into Soil?

E2.2 E1.2 A1.2 A1.4About 40 minutes
Learning goals
  • I can name substances that people add to soil and substances that soil absorbs.
  • I can describe whether each substance helps or harms soil health.
  • I can explain why too much of a helpful thing can harm soil and water.
  • I can do a fair test about salt and plants.

Words to know

substance
Any kind of material or stuff, like water, salt, oil or compost.
absorb
To soak something up. Soil absorbs rain.
fertilizer
Plant food that people add to soil to give plants more nutrients.
manure
Animal droppings. Aged (old) manure is added to soil as plant food.
mulch
A covering, like wood chips, straw or leaves, spread on top of soil.
pesticide
A chemical made to kill pests, like insects or weeds that harm crops.
pollution
Something harmful or dirty that gets into the air, water or land.

Soil soaks it up

Soil is like a giant sponge. Rain soaks into it. Melting snow soaks into it. But so does anything that is spilled, sprayed or dropped on it!

Some substances are added to soil on purpose to help plants. Others are absorbed (soaked up) by accident. Some help soil health, and some harm it. Today you will be a soil health inspector.

Substances people add on purpose

  • Water. Plants need water. Gardeners and farmers water their soil when it is dry.
  • Compost. Rotted food scraps and leaves. It adds humus and nutrients and feeds soil living things. (You'll learn to make it in the last lesson!)
  • Manure. Aged animal droppings from cows, horses or chickens. It adds nutrients and humus.
  • Fertilizer. Plant food that gives plants extra nutrients, like nitrogen, so they grow bigger.
  • Mulch. Wood chips, straw or leaves spread on top. It keeps soil damp, blocks weeds and protects soil from erosion. Over time it decomposes into humus.
  • Lime. Crushed limestone rock. Farmers add it to soil that is too sour (acidic) for their crops.
  • Pesticides and weed killers. These kill insects or weeds that harm crops. But they can also harm helpful living things, like earthworms and bees, if they are used too much or the wrong way.

Substances soil absorbs by accident

  • Road salt. In winter, salt is spread on roads and sidewalks to melt ice. In spring, the salty meltwater soaks into the soil nearby. Too much salt dries out roots and harms soil living things. That is why grass beside some roads and sidewalks turns brown or dies.
  • Oil and gasoline. These can leak from cars and machines or be spilled. They coat soil, harm living things, and can soak down into groundwater.
  • Paint, cleaners and other chemicals poured on the ground or into a ditch.
  • Litter and plastic. Plastic does not decompose like leaves. It breaks into tiny pieces that stay in the soil for a very long time.
  • Air pollution. Smoke and gases from some factories and cars mix with rain. The polluted rain can make soil more sour (acidic) and harm plants.
A sidewalk sprinkled with road salt next to a lawn where the strip of grass along the edge has turned brown.
Salt from the sidewalk soaked into the soil nearby. Notice how the grass closest to the sidewalk turned brown while grass further away is still green. AI-generated image
SubstanceAdded on purpose or absorbed by accident?Effect on soil health
compostaddedhelps: adds humus and nutrients, feeds living things
aged manureaddedhelps: adds nutrients and humus
mulchaddedhelps: keeps soil damp, stops erosion
fertilizeraddedhelps plants grow, but too much can harm soil and water
pesticidesaddedkill pests, but can harm helpful worms and insects
road saltabsorbedharms: dries out roots, harms living things
oil and gasolineabsorbedharms: coats soil, poisons living things
litter and plasticabsorbedharms: does not decompose
Substances and soil health

Too much of a good thing

Even helpful substances can cause harm if we use too much:

  • Too much water fills up all the air spaces. Roots can't breathe, and the soil gets soggy.
  • Too much fertilizer can't all be used by plants. Rain washes the extra into creeks and lakes. There it feeds algae (tiny water plants), which can grow so much that they make the water green and smelly and harm fish. This has happened in parts of Lake Erie.

That is why farmers and gardeners try to use the right amount, at the right time, in the right place.

1. Too muchfertilizer on a field2. Rain washesthe extra away3. It flows intoa creek4. Algae growtoo much in the lake
Too much of a good thing: extra fertilizer washes off the field, into a creek, and then into a lake, where it feeds too much algae.
Worked example

Let's sort: helpful or harmful?

Sort these: compost, spilled motor oil, mulch, plastic wrappers, aged manure, road salt.

  1. Ask: "Does it add humus or nutrients, or protect the soil?" If yes, it is helpful.
  2. Compost: adds humus and nutrients. Helpful. Mulch: protects and becomes humus. Helpful. Aged manure: adds nutrients. Helpful.
  3. Ask: "Does it poison living things, dry out roots, or never break down?" If yes, it is harmful.
  4. Spilled motor oil: poisons living things. Harmful. Plastic wrappers: never decompose. Harmful. Road salt: dries out roots. Harmful.

Helpful: compost, mulch, aged manure. Harmful: motor oil, plastic wrappers, road salt.

Worked example

Let's do a fair test: Does salt harm seeds?

Ana wonders if salty water stops seeds from growing. How can she test it fairly?

  1. Prediction: "Seeds with salty water will not grow as well."
  2. She fills 2 cups with the same potting soil and plants 10 radish seeds in each, at the same depth.
  3. Both cups sit in the same sunny window and get the same amount of water each day (2 spoonfuls).
  4. The only difference: Cup A gets plain water. Cup B gets water with 1 spoonful of salt stirred into a cup of water.
  5. After 1 week: in Cup A, 8 of 10 seeds sprouted. In Cup B, only 1 of 10 sprouted, and it looked weak.
  6. 8 − 1 = 7 more seeds grew with plain water.

Salt harmed the seeds. This helps explain why soil beside salty winter roads can't grow healthy plants.

Cup A: plain water8 of 10 sproutedCup B: salty water1 of 10 sproutedEach oval is one radish seed. A shoot means it sprouted.
Ana's results. With plain water, 8 of 10 seeds sprouted. With salty water, only 1 of 10 did.

Safety first

  • Never touch, smell or play with oil, gasoline, paint, pesticides or cleaners. Only grown-ups handle them, following the label.
  • Never pour chemicals on the ground or down a storm drain. Grown-ups take them to a household hazardous waste drop-off.
  • Wash your hands after touching soil and after the salt test. Don't taste the salty water.
  • Wear gloves if you pick up litter, and never pick up sharp things.
Just for fun

Why did the gardener give the soil a bag of compost for its birthday?

Because it is the gift that keeps on growing!

Hands-on activity

Salt and seeds test

You need: 2 small cups with holes in the bottom (a grown-up pokes them), potting soil, 20 small seeds (radish, grass or beans work well), salt, water, a spoon, labels.

  1. Fill both cups with the same amount of soil. Label them Plain and Salty.
  2. Plant 10 seeds in each cup, at the same depth.
  3. Mix 1 spoonful of salt into a cup of water to make salty water.
  4. Every day, water the Plain cup with 2 spoonfuls of plain water and the Salty cup with 2 spoonfuls of salty water.
  5. Keep both cups in the same place.
  6. Each day for a week, count how many seeds have sprouted. Record in a table.
  7. What did you find out? How does this connect to road salt in winter?

Bonus: Next winter, look at the grass beside a salted sidewalk in spring. Is it as green as the grass farther away?

Your turn

1

Name two substances people add to soil on purpose to help it.

2

Name two substances that can get into soil by accident and harm it.

3

How does road salt harm soil and plants?

4

How does mulch help soil?

5

Why is plastic litter a problem in soil?

6

What can happen if a farmer uses too much fertilizer?

7

What is the one thing Ana changed in her test?

More practice: warm-up

1

Helpful or harmful: compost?

2

Helpful or harmful: spilled gasoline?

3

What does absorb mean?

4

What is manure?

5

Who should handle chemicals like paint or pesticides?

More practice: on your own

1

Why do farmers add lime to some soils?

2

Explain how water can be helpful and harmful to soil.

3

Why might a pesticide harm soil health even if it kills only "bad" bugs on purpose?

4

A family washes paintbrushes and dumps the water on the lawn. What could happen? What should they do?

5

Ana's plain-water cup had 8 sprouts. Her salty cup had 1. What can she conclude?

Challenge

1

Why do farmers try to use the right amount of fertilizer, at the right time and in the right place?

2

Grass along a busy road is brown every spring, but grass far from the road is green. Give a possible reason and a way to test it.

3

Is fertilizer helpful or harmful? Explain why the answer is "it depends".

Check your understanding

Quiz

1.

Which substance helps soil health?

2.

Road salt harms soil because it...

3.

What happens when too much fertilizer washes into a lake?

4.

Mulch is spread...

5.

In a fair test about salt and seeds, what should be different between the two cups?

6.

Leftover paint should be...

For parents and teachers

Big idea (E2.2): Many substances are added to or absorbed by soil: water, compost, manure, fertilizer, mulch, lime and pesticides on purpose; road salt, fuels, household chemicals, litter and air pollution by accident. Each affects soil health, and helpful ones can become harmful in excess (water, fertilizer). This links to the human impact in E1.2.

How to help: The salt-and-seeds test is quick and convincing (radish or grass sprouts in 3 to 5 days). Ask your child to name the one thing changed and the things kept the same (A1.2). Notice salt use on your own sidewalk in winter and talk about using only what is needed.

Common difficulties:

  • Thinking all chemicals are bad and all natural things are good. The amount matters. Too much water or manure can cause harm too.
  • Thinking spilled things disappear. They soak in and can stay or travel to groundwater.

Safety (A1.4): Children should not handle fuels, pesticides, paints or cleaners. Store them out of reach. Use only kitchen salt for the experiment and don't let children drink the salty water.