Lesson 1
Impact of Soil Type on Seed Germination and Plant Growth (Study)

Background Information:

Clay based soils tend to have a reddish or orange color to them due to a higher iron content. Clay soils have smaller soil particles and therefore do not drain well. They are more compact and make it harder for roots to grow through. Typically soils that are high in clay are considered a lower quality soil for growing plants.

Sandy soil is the opposite of clay soil in that the soil particle size is larger allowing for water and nutrients to flow through it quickly. As a result this type of soil dries out quickly and is also consider a lower quality soil.

The “gold standard” soil is called loamy soil and is comprised of 20% clay, 40% sand, and 40% silt (medium sized particles). This is good for plants because it has the correct ratio of particle sizes that allow for the retention of water and nutrients, and enough space between the particles for roots to grow easily and obtain the oxygen they need.

For this lab sandy soil can be obtained at a nursery. This soil will be labeled potting soil for Succulents, which typically grow in sandier soils. Loamy soil can be substituted with regular potting soil. Clay soil will have to be dug from a local source. If the soil is not a red or orange color, it may still have a lot of clay in it. High clay content soil, when wet, can be squeezed and it will retain the shape without falling apart. It also has a slimy quality when wet. This is the element of soil that makes it really stick to your boots. If you live in an area where you have good soil, digging down below the top soil usually results in a larger clay content as the clay particles tend to move down through the soil over time and compact deeper in the earth (its like the crumbs at the bottom of a bag of potato chips).

Materials: See the general Plant Germination and Growth Study for detailed information.

  1. Seed for germination (12 larger seeds per group).
  2. 12 containers for growth. Egg cartons would work well. Use 4 cells for each type of soil.
  3. 3 types of soil.
  4. Spray bottles or wash bottles
  5. Growing area
  6. Rulers and Permanent Markers
  7. Scissors, electronic balance, drying trays if measuring biomass.
  8. Simple soil testing kits (Luster Leaf Rapitest Soil Test Kit) can be used to test for soil nutrients to help with discussion questions.
Continuous Procedure: (Decide whether information will be recorded every day or every other day, or simply by the date. It is not necessary to record the information every day once the seeds have germinated).

  1. Each day record if the seeds have germinated or not and calculate the percent germination.
  2. Once a seed has germinated, the height should be recorded each day and recorded. (See Student Handout below for instructions on measuring and calculating data).
  3. Each container should be watered as necessary. The soil should look and feel damp but not be swampy. As the plants grow, they will need more water.
  4. Continue this procedure until at least 5 data points are obtained.

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