What's in your soil?
What is dirt? To young children, dirt is something to play in; to adults, it's something that the dog tracks into the house.
Gardeners, however, recognize that dirt is soil, the vital substance that promotes healthy plant growth. But what, exactly, is soil? Soil, which is commonly called dirt, is the thin layer at the top of earth's crust. Soil contains air, water, humus (HUE-miss), rocks and minerals. The proportion of these soil components varies geographically.
Aside from air and water, humus, rocks and minerals are the components most commonly associated with soil. Humus consists of decomposed plants and animals (organic materials). While humus comprises approximately 5% of the soil, it is a major source of nutrients for plants. In addition, humus increases the soil's ability to absorb and retain water.
Rocks and minerals constitute approximately 45% of the soil and are responsible for variations in geographic soil composition. Sand, silt and clay are the three smallest rock sizes, with sand being the largest, followed by silt, and clay being the smallest particle size. The ratio of these three rock sizes determines soil texture.What is the soil composition in your garden? To find out, gather the family and conduct this simple experiment! Collect the necessary supplies; you will need a mason jar or 12 ounce clear container with a lid, a shovel or hand trowel, a glass of water and a permanent marker pen. Take the family and supplies into the garden. Select a site free of grass, rocks or mulch. Angle the shovel or hand trowel straight into the soil to obtain a representative sample of soil. Place this soil specimen into the jar, using enough soil to fill the jar about two-thirds full. Pour enough water into the jar to cover the soil, leaving a small air space at the top of the jar. Tightly place the lid onto the jar and shake the jar for approximately 30 seconds. Allow the jar to remain undisturbed for approximately 24 hours. After collecting the soil specimen, encourage the family to pick up a handful of soil and feel the soil with their fingertips. Does the soil feel gritty or greasy or flaky? Typically, sandy soils feel gritty, while silty soils feel floury when dry and greasy when wet. Clay soils always feel greasy.When you return indoors, place the jar somewhere it will not be disturbed. As the soil settles, observe how the soil separates into layers. Use a permanent marking pen to draw a line on the jar around each layer. Your soil most likely will settle into four separate layers. The bottom layer is the largest rock, which is the sand. You may see small black specks throughout this layer. On top of the sand is the silt. The third layer from the bottom is the smallest rock size, clay. This layer may be the lightest color of the three layers. On the very top rests the fourth layer, which is the humus. This layer is darkly colored and may either be layered on top of the silt or floating on top of the water.
Now you have discovered the composition of your soil. What do these results tell you? Based on proportions of sand, silt, clay and humus, you can understand how your plants are affected by the soil. Soils with a high proportion of clay do not absorb water as quickly as soils with a low proportion of clay. For soils with high clay content, water plants slowly over a longer period of time to allow for water absorption into the roots. Because soils dense in clay retain water, avoid planting trees, shrubs and perennials that require adequate drainage. Soils with a high proportion of silt tend to drain well but remain moist. Most plants grow well in this soil. Soils with high humus content may not have the structure to support deep root growth. Balancing out these soil layers through regular management practices such as adding compost, keeping the soil aerated and watering as needed provides a healthy environment for plants to grow and thrive. Penn State Extension offers in-depth information on soil quality and soil health (https://extension.psu.edu/soil-quality-information).The soil jar test is a simple experiment to help families understand their soil. This activity engages children in gardening practices, such as learning about the importance of soil, understanding ratios and proportions, and using gardening tools. The best part of the learning experience is that everyone gets to dig in the dirt!If you would like more information on soil composition and quality, call the Master Gardener Garden Hotline at 724-287-4761, ext. 7, or email the Master Gardeners at butlermg@psu.edu.Helen Erdner is an elementary school teacher and a Penn State Extension Butler County Master Gardener trainee.
