Life in Soil
This is decayed plant and animal material that helps soil hold nutrients.
Humus
What is the topmost organic layer of soil called?
O horizon (humus layer)
Name the three main soil textures by particle size.
Sand, silt, clay.
What is the word for breaking rock into smaller pieces without moving them?
Weathering
If a garden has heavy clay soil, name one problem the gardener might face.
Problem: Poor drainage (waterlogging) or hard-to-work sticky soil.
Name one small living organism found in soil that helps break down dead plants
bacteria, fungi, earthworms, protozoa (any organism who lives underground).
List the five soil horizons from top to bottom in order.
O horizon (humus), A horizon (topsoil), B horizon (subsoil), C horizon (parent material), R horizon (bedrock).
Which soil particle is largest and which is smallest?
Largest → Sand; Smallest → Clay.
What process moves soil particles from one place to another (examples: water, wind, gravity)?
Erosion
Give one easy way to improve heavy clay soil for planting vegetables.
Add organic matter like compost or build raised beds to improve drainage and structure.
Explain why earthworms are helpful to soil (one or two sentences).
Earthworms aerate (let the soil breathe...help air flow) the soil by making tunnels and mix organic matter into soil, improving structure and helping roots get air and water.
Which horizon contains most plant roots and is richest in humus?
A horizon (topsoil).
What kind of soil is a mixture of sand, silt, and clay that is best for gardening?
Loam
What force or process is responsible for transporting weathered rock and soil particles from one location to another?
Erosion
Why would a farmer worry about very sandy soil when growing crops?
Sandy soil drains too fast and does not hold nutrients well, so plants may dry out and lack minerals.
Give two reasons soil organisms are important for plants
(1) They break down dead plants into nutrients plants can use. (2) They help make soil crumbs that let air and water move through.
What does the "R" in the soil horizons stand for, and what is it made of?
R = Bedrock; it is unweathered rock beneath the soil.
Compare sandy soil and clay soil in water drainage.
Sandy soil drains quickly because particles are large with big spaces; clay drains slowly because particles are tiny and pack tightly, holding water.
Explain how weathering and erosion work together to form soil.
Weathering breaks rocks into small pieces; erosion moves those pieces to new places. Over long time, the broken rock mixes with organic matter to form soil.
A construction company plans to build on land with mostly clay. Name two potential problems for building.
Problems: poor drainage causing foundation shifts; soil can expand/contract causing cracks. Solutions: install proper drainage, use deeper foundations or soil replacement/amendment.
Describe how soil acts as a habitat and give one example of an organism that lives there.
Soil is a habitat because it provides food, water, and space for living things. Example: earthworms live in soil and eat decaying leaves.
Explain why the B horizon (subsoil) often has fewer organisms than the A horizon (topsoil).
The B horizon is deeper and has less organic matter because leaves and plant roots are mostly near the surface; fewer organisms and less humus reach that layer.
A soil sample holds water for a long time and feels sticky when wet. Which soil type is it and why?
Clay soil — because its very small particles hold water tightly and feel sticky when wet.
Estimate roughly how long it takes to form a thin layer of new soil and explain why it takes so long.
It can take hundreds to thousands of years to form just a few centimeters of soil because weathering and organic matter build up very slowly.
As a soil scientist, you must choose a location for a community garden. Give two features of the best location and one reason to support your choice.
Best location features: (1) Loamy soil or soil that can be amended with compost, (2) Good sun exposure and access to water. Reason: Loam holds water and nutrients while draining well, and sunlight and water are needed for vegetables to grow.