STEM Club: Let’s Get Dirty – Soil Horizons & Particle Size

Soil is the part of the ground where plants grow. Soil is a mixture of tiny particles of rock and rotting plant and animal material, with water and air between them. Soils help plants grow in two ways. First, soil holds the plants into place. Second, soil contains nutrients that plants need in order to survive. These nutrients include water, phosphorous, nitrogen, and potassium.

Over the course of the next few weeks, STEM Club will be investigating soil ecology as a part of the Year of Soils. I’ve shared a few of our past endeavors relating to soils here:

Soil Ecology Activities for Middle School

Cycles and Ecosystems {Free Printable}

Soils Support Urban Life: Rain Gardens & Composting

Soils Support Agriculture: Ideas to Integrate Writing

STEM Club: Let's Get Dirty (Soil Ecology) @EvaVarga.net

Today, I share a lesson on soil horizons and particle size.

Soil Horizons

Soil particles vary greatly in size. The largest particles settle to the bottom first. The fine particles settle slowly; some are suspended indefinitely. The amount of open space between the particles has much to do with how easily water moves through the soil. This also determines how much water the soil will hold, which has a major effect on the type of plants that can grow in the soil.

STEM Club: Let's Get Dirty (Soil Ecology) @EvaVarga.net

Things to look for in soil are color, texture, structure, depth, and pH. A general soil profile is made up of a litter layer, A horizon, B horizon and C horizon. A soil sampling device (pictured in the collage above) allows you to gather data on the soil makeup on any site.

Soil Particle Size

Soil scientists classify soil particles into sand, silt, and clay. Scientists use these three components and the calculated percentages on the texture triangle to determine the textural class of the soil at a given site.

A soil’s texture depends on the size of its particles and living things depend on the right texture to thrive in the soil. Every soil type is a mixture of sand (2mm – 0.05mm; feels gritty), silt (0.05 – 0.002mm; feels like flour), clay (Smaller than 0.002; feels sticky when wet), and organic matter. Squeeze some soil between your fingers. Is it crumbly? Sticky?

STEM Club: Let's Get Dirty (Soil Ecology) @EvaVarga.net

Let’s Get Dirty ~ Terrestrial Soils

One of the best activities to engage kids in the study of soil ecology is the sample the soils around your home or school yard. Begin by asking the following questions:

1.  Are there different types of soil near your home?

2.  What texture class is this soil?

3.  What is the particle size make-up of this soil?

The answers generated prior to the investigation are part of your hypothesis. Record your ideas in your science notebook before you begin and give reasons. Why do you suppose the soil in your yard is predominately sand? What experience or prior knowledge do you have to help you make this statement?

Materials

  • 1 Soil probe
  • 1 Metric ruler
  • 1 Quart jar with lid
  • 1 Set index cards for diagrams

Procedure

  1. Use the soil probe to collect soil cores as deep as possible from a predetermined site.
  2. Diagram and measure the depth of each layer or horizon in your sample.
  3. Fill the quart jar at least half and no more than two thirds full.
  4. Fill the rest of the jar with water, seal tightly and shake vigorously for 10 minutes. Let the jar stand for 24 hrs.
  5. The next day, mark the soil layers of each sample on an index card placed behind the bottle. Mark the top of the soil and the points where the layers change. Calculate the percent of sand, silt and clay in your sample. To do this, measure the following marks you made on the card: entire height, sand (bottom) layer, silt (middle) layer, and clay (top) layer. Then take the height of each layer by the total height and multiple by 100. Record the figures on the data sheet.

STEM Club: Let's Get Dirty (Soil Ecology) @EvaVarga.net
Analysis of Results

  1. At which site was the soil the most sandy? silty? mostly clay?
  2. Do you think that this is a trend and would be found at other sites? Explain.
  3. What are some factors that may change the results of this experiment? Explain.

Conclusions

  1. Did you achieve your hypothesis? Explain.
  2. What did you learn by doing this exercise?
  3. Do you think the soil will be the same at other sites (park, forest, meadow, near the shore of a lake or river, etc.)? Design an inquiry project to learn more.

Soils Support Agriculture: Ideas to Integrate Writing

This month’s International Year of Soils theme is Soils Support Agriculture. The soil is the ultimate source of nutrients our bodies need. The vitamins and minerals that are a necessary part of our diet come from plants that have, in turn, gotten those same vitamins and minerals from the soil. Soils support agriculture by serving as the foundation of where we grow food.

soilssupportagWriting Contest

Each year, the California Foundation for Agriculture in the Classroom sponsors a writing contest for youth. Their goal is to promote reading, writing and the arts, while also furthering the understanding of agriculture in our lives.

As a part of our Writer’s Workshop, I encouraged all of my students to submit an entry. Much to our delight, we recently learned that my son’s story was selected as a regional winner.

Papa’s Oranges

The young boy looked out the window and could see nothing but trees for as far as he could see. He knew he wasn’t at home. He glanced at the clock next to the bed, it was 7:00 a.m. The only thing he remembered was that he fell asleep in the car going to visit his papa. “I guess this is it,” the boy said to himself.

Every tree he could see was covered with oranges. His mom had said that his papa had a large orchard so he guessed this was his house. He jumped out of bed, threw on his shoes, and ran outside. “Mom, Dad, and Papa must not be up yet,” he thought.

He kept running until he could not see the house very well. He reached up and picked one of the oranges. He peeled it, the juice overwhelmed his taste buds. He wiped his face with his sleeve as the juice dripped down his chin.

“Is it good?” asked someone from behind him.

The boy jumped in surprise. “Yes, very.” The boy noticed it was his grandfather. “I thought you were asleep!” the boy cried.

“Well I am going for a walk. Would you like to join?” asked his grandfather.

“It would be my pleasure.”

They started walking even further into the orchard. Only then the boy saw what his papa was wearing. He had on a brown Fedora that was placed a little back on his head. He wore a tan shirt with a weathered leather jacket, long brown pants, and for some reason a whip was coiled on his hip.

“What’s that for?” the boy asked, pointing.

“Oh, my whip? It’s for Yankees – people that poison trees and pick all the fruit,” his papa answered with a grin.

They boy asked more questions as they continued to walk. “When I was pealing the orange, why was it so hard?”

“Well, you were in the juvenile patch so the orange peels are thicker. Those trees can grow to be 20 to 30 feet tall. Orange trees can bear fruit they reach their full height. Right ahead of us is the mature patch,” answered his papa.

As they continued to walk, his papa kept on talking about how the oranges grow. “I grow two kinds of oranges. Washington navels for an early season harvest and Valencia for a later season harvest.”

“How do you know when to harvest them?” the boy asked.

“Oranges develop their sweetness over time on the tree. I like to taste them each week. That’s how I know they are ready.”

“I love oranges, Papa. I like helping you, too.”

“I was thinking that when I retire you could take over,” his papa said as they returned to the house.

“You are joking!” the boy said disbelievingly.

“No, I am not. Are you interested?”

“Yes!!” the boy yelled.

“I thought you would like to have it.”

The boy then ran inside to tell his parents.

Lesson Plans

The Chemistry of Fertilizers – California Foundation AITC ~ Hands-on experiments, activities, practice problems, discussions and writing assignments are incorporated as students learn to break compounds into ions, make a fertilizer and test several fertilizers for phosphate content.

Chemistry in Plant Nutrition and Growth – Alaska AITC ~ Lesson plan with information, tables, diagrams, and questions about plant nutrients in soil.

Soil Sam – Illinois AITC ~ Students make a “Soil Sam” with a baby food jar to hold the soil and grass seeds planted to grow “hair”. Includes suggested additions to learn about fertilizers.

Soils Support Urban Life: Do Your Part with Rain Gardens & Composting

Soil is a complex mixture of minerals, water, air and organic matter that performs many critical functions. In the United States, more than 80 percent of the population lives in cities or suburbs. While the downtown areas of cities are covered with asphalt and concrete, there are still lawns, trees, gardens, and parks. Under all this city space, even under the concrete, is soil.

soilsurbanlifeSoils Support Urban Life

Before we began using pipes, drains, pumps, and other infrastructure to manage stormwater, nature provided the “green infrastructure” to slow, filter, and move water to where it belonged. In forests and wetlands, water is still managed naturally. The foundation of this network is the soil. It is the drain, the pipe, the pump, and the water treatment plant all in one.

As urban areas have grown and we’ve continued to pave over our soils, demands on both natural and manmade stormwater management systems have increased. The last few decades have brought a shift from traditional “capture, convey, and treat” drainage systems. Instead, many cities are beginning to focus on more sustainable systems to manage storm water runoff.

Often referred to as “green infrastructure”, these sustainable systems include rain gardens, living roofs, and the growing trend to plant vegetation native to the region. These practices can delay the arrival of water that reaches the sewer system and thereby reduce flooding.

The biggest benefit green infrastructure, however, is the potential reduction of pollutants entering the storm water system. Pollutants like nutrients (from fertilizers), road salt, and bacteria, can negatively affect aquatic life and public health. Green infrastructure captures these pollutants, especially those that might run off at the beginning of a storm.In both of the cities I have called home in the past few years, a few public buildings have even converted their roof tops to green space. These green roofs not only help to reduce pollutants but provide habitat for pollinators and small birds. In addition, they can provide learning spaces to learn about native plants and sustainable agricultural practices (drip irrigation, etc).

Bring it Home

The Soil Science Society of America recommends that urban dwellers consider rain gardens for their yards and compost their appropriate food wastes. Help the soil serve you by making rain gardens, making and using compost, and making an urban garden. Here are several resources and lesson plans to get you started:

  • Do the Rot Thing – Download this free composting curriculum to bring the science of composting into your curriculum
  • Build a Two-Can Bioreactor or small-scall indoor composting unit, or on a smaller scale consider a …
  • Soda Bottle Bioreactor that will enable students to design and carry out individualized research projects, comparing variables such as reactor design, moisture content, and nutrient ratios of mixtures to be composted.
  • Soil Science – Learn about basic soil science, and then explore some unique characteristics of soils found in urban areas.
  • Exploration of Run-off and Infiltration – In this unit, students design and conduct experiments on runoff and infiltration, either outside or in the classroom
  • Nourishing the Planet – Download the free soil science curriculum to help students realize the challenges of feeding a growing world
  • Dig It! Secrets of Soil – Visit the Smithsonian exhibit’s website to access 10 online interactive learning modules