Clay soil has a bad reputation for being heavy and having poor drainage, and when it dries out, it becomes hard and compacted. However, clay is an important component of soil, as it attracts important nutrients and helps the soil hold water for your growing plants.
What Is Clay?
There are three common types of soil: sand, silt and clay. Sand has the largest particle size, while clay has the smallest particle size. It has a smooth texture and tends to be very dense. Clay soil particles are created through erosion and weathering. While some soils are mostly made of clay, it is also common for soil to consist of a combination of soil types.
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Nutrient Retention Qualities
One of the best qualities of clay is that it attracts and retains nutrients. Nutrients tend to leach out of sandy soils, so having some clay in the soil helps your plants thrive. This is due to the high cation exchange capacity (CEC) of clay soil. CEC measures the negative charges on the surface of the soil. The more negative charge, the more the soil can attract and retain key soil nutrients, such as calcium, magnesium and potassium.
CEC does not guarantee that the nutrients are in the soil, only the ability of the soil to retain the nutrients that are present. If you are unsure about the nutrient levels in your soil, conduct a soil test through your local extension office.
High Water Retention
Clay soil is able to retain water well, which keeps the area moist to provide a constant supply of water to the plants' roots. In addition, water moves slowly through clay. This means that you need to apply water slowly when irrigating your plants.
While the ability to hold water is beneficial to plants, there is a downside. If you overwater or get a large rain storm, clay soils can easily become flooded.
Amending Clay Soils
Despite these benefits, soil that has too much clay, generally more than 50 percent, can be difficult for the growth of plants. It holds water very well, but due to the dense structure of clay soil, roots may have trouble growing through the clay. In addition, there may not be enough space in the soil for the roots to get the oxygen they need. Microbes and organisms in the soil also need oxygen to live, so if you think your soil has too much clay, there are some things you can do to improve the soil. Plus, the soil surface can develop a crust, and the soil can get hard.
The best way to improve clay soil is by adding organic material. Some good options include compost, grass clippings and other yard trim, mulch and bark. Manure is also an effective option, but there are some considerations when using this option. If the manure is fresh, you shouldn't use it to amend the soil for planting vegetables. If the manure is composted, be aware that it may become high in salts.
Gypsum is sometimes recommended, but there is no real evidence that it effectively corrects clay soil. Gypsum does contain calcium and sulfur, however, so if your soil is deficient in these nutrients, it may be beneficial.
- Clemson University Cooperative Extension Service: Soil Conditioning – Establishing a Successful Gardening Foundation
- University of Maryland Extension: Soil Health, Drainage, and Improving Soil
- Ohio State University Extension: Calculating Cation Exchange Capacity, Base Saturation, and Calcium Saturation
- Elisabet Ney Museum: The Importance of Clay
- Utah State University Forestry Extension: Gardening in Clay Soils