Different Types of Soil and Their Effect on Plant Growth
What is Soil?
Before the students learn about the importance of soil, they may think it is "just dirt," but soil is a critical component of land ecosystems that supports the growth of vegetation. Depending on the proportion of the different components, soil can be rich and fertile, or poor and less able to support plant life.
Soil Composition - Soil is a complex mixture of rock fragments, organic material, air and water.
Soil Texture - The rock fragments that make up soil are divided into three types according to size: sand particles are the largest, silt particles are next in size, and clay particles are extremely small. The texture of the soil determines how well it drains. Soils that are predominantly clay are very heavy, have poor drainage, and do not contain very much air, while sandy soil with a large percentage of organic matter drains well and has spaces so that roots can spread out and grow.
Soil Fertility - Soil fertility is the ability of soil to supply needed nutrients to plants. Three of the most important nutrients are nitrogen, phosphorus and potassium. The rock fragments and organic matter (humus) in the soil provide nutrients that plants need to grow. Humus comes from decayed plant and animal matter that has been broken down by decomposers such as bacteria and fungi living in the soil.
Activity to Determine What Soil is Best for Plants
In this activity, students will compare the growth of bean plants in different types of soils. It can be done as a group activity, with each group setting up their own series of pots with different soils. If classroom space is limited, the teacher can set up the experiment for the whole class to observe.
- Bean seeds or other seeds that germinate easily and quickly.
- Small pots or paper cups with holes in the bottom for drainage.
- Sand, pea gravel and potting mix. If available, include other soil samples representing different soil types, such as clay and loam. Students may wish to bring in samples from their own yards to test.
1. Prepare identical pots containing different types of soil.
2. Plant four bean seeds in each pot.
3. Give each pot the same amount of water and expose to the same amount of sunlight.
4. Students will observe the germination and growth of the bean plants over time, and record their observations in their science journal or on a worksheet.
5. Students will compare the growth of the plants in different types of soil and conclude which soil type was best for plant growth.
6. Have students explain their results. The seeds should grow poorly in the pea gravel and sand because these provide very few nutrients, while the potting soil is best suited for plant growth because it contains nutrients that plants need.