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CropTalk: Base Saturation: An Important Soil Fertility Calculation

March 2019

Published on Tuesday, March 5, 2019

Many farm operations have a soil fertility testing program every 3 to 4 years. Whether you do your own soil sampling or hire a trusted professional, the soil test report can often appear as a complex dataset. A standard soil test report will usually provide values such as pH, percent organic matter (OM), phosphorus, and potassium; however, other data can be extremely valuable for a better understanding of the soil’s ability to hold and supply nutrients, as well as the soil fertility balance. See Figure 1 for an example of a complete soil test report.

Cation Exchange Capacity (CEC) and Base Saturation (BS) are very important values on a soil test report. This data often requires an additional fee. However, it’s important to ask for these values when consulting with your soil testing service or the lab where samples are submitted because they provide further guidance for developing a proper soil fertility plan.

CEC is usually well understood by many farmers because it is strongly correlated with soil texture (concentration of sand, silt, and clay). Furthermore, the amount and type of clay, along with percent OM, have a significant effect on CEC. Soils with high CEC (~20+) generally have higher water-holding capacity, clay content, OM, and nutrient-supplying power. Soils with low CEC (<12) typically require multiple timely nutrient applications throughout the growing season for maximum crop production, especially for nutrients such as nitrogen and potassium.

It’s important to realize that reported CEC values are based on a chemical extraction process, which measures the amount of positively-charged ions (calcium, magnesium, potassium, hydrogen, and sodium) in the soil. The more cations that are extracted, the higher the reported CEC values. Using the CEC from the nutrient extraction process, one can calculate the BS. BS represents the percentage of the CEC that is occupied by the basic cations mentioned above.

Base saturation correlates with many other values on the soil test report, but it is a better prediction of nutrient availability than total nutrient content. Total pounds per acre of a specific nutrient does not factor in the amount of negatively-charged particles in a given amount of soil (the CEC).

The calcium BS is usually strongly correlated with soil pH, pounds per acre of calcium, and BS of hydrogen. If calcium occupies less than 65 to 75 percent of the CEC, soil pH and pounds per acre of calcium are usually below optimum levels for maximum nutrient availability and crop production. When calcium BS is below optimum, the BS of hydrogen is usually higher than optimum due to greater soil acidity.

The amount of calcium available in the soil is very important for cell division and plant growth. In areas where soil magnesium levels have gotten too high (i.e. 20%+ BS), high-quality calcium products, such as “ag lime,” “pell lime,” or “calcitic lime” (calcium carbonate) or gypsum (calcium sulfate) can help exchange magnesium that is held in the soil with calcium. This is important because when soil magnesium levels are elevated, potassium supply and availability to the plant become limited.

Limited potassium supply will have direct effects on plant growth and grain yield due to lower drought tolerance, weaker stalks/stems, and less resistance to plant diseases. In your area, you may be struggling with other nutritional issues, such as excessively high hydrogen BS or low potassium BS. These issues can be managed with the proper nutritional product depending on your operational capabilities. Contact your local Beck’s representative for help interpreting your soil test and more information on options and solutions that best fit your needs.

When managing BS and soil nutrition for proper balance, it’s important to understand the ease of cation replacement. In other words, understanding which cations have the ability to replace other cations will help determine the correct soil fertility products to use. Figure 2 illustrates the order of cation replacement in the soil. Simply stated, aluminum (Al) and calcium (Ca) are held more tightly by soil particles than sodium (Na) and potassium (K).

This also indicates that magnesium (Mg) is released from soil particles more easily than calcium (Ca). If you are trying to raise soil pH and leach magnesium out of the soil because the magnesium BS is too high, a high-quality calcium product with as close to 0 percent magnesium as possible would be desired. If you do NOT want to change soil pH, a product like gypsum would be an effective product to help displace magnesium with calcium.

Soil fertility can get out of balance for many possible reasons; however, the most common reason is lack of proper fertility management. In addition, the natural soil mineralogy in some areas can create significant management challenges for balancing nutrients. Lastly, if a proper soil nutrition balance is achieved, plants must still be able to access the nutrients with an adequate root system, proper soil moisture, and lack of soil compaction.

Please contact your local Beck’s representative for further information on soil fertility tests and product recommendations for managing and maintaining a proper balance of nutrients in your fields.

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Author: Chad Kalaher

Categories: CropTalk, 2019


Chad Kalaher
Chad Kalaher>

Chad Kalaher

Beck’s Hybrids team sales agronomist for 22 counties in NE ¼ of IL and 7 counties in NW IN. Raised on grain and livestock farm in southern IL. B.S. Agronomy 1995 – University of Illinois, M.S. Weed Science 1997 – North Carolina State University. Previous positions in seed industry as researc

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Full biography

Beck’s Hybrids team sales agronomist for 22 counties in NE ¼ of IL and 7 counties in NW IN. Raised on grain and livestock farm in southern IL. B.S. Agronomy 1995 – University of Illinois, M.S. Weed Science 1997 – North Carolina State University. Previous positions in seed industry as research agronomist, district, and regional sales manager.


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