Education

Understanding Soil Base Saturation: The Role of SO4 Pelletized Gypsum and 98G Pelletized Limestone

One of the most common questions we receive at Calcium Products pertains to soil base saturation, particularly the Calcium to Magnesium ratio. Growers frequently ask how they can influence ba

se saturation using SO4 Pelletized Gypsum and 98G Pelletized Limestone to build calcium levels and decrease high magnesium concentrations. Like many aspects of soil science, this process requires time and persistence. To fully understand how SO4 and 98G impact base saturation, it is crucial to first grasp what base saturation represents and how factors like Cation Exchange Capacity (CEC), soil pH, and Organic Matter play a role.

What is Soil Base Saturation?

Soil base saturation is the percentage of soil exchange sites (CEC) occupied by basic cations such as Calcium (Ca), Magnesium (Mg), Potassium (K), and Sodium (Na). The sum of these cations represents the total base saturation of a soil sample. However, base saturation levels do not always add up to 100 due to the presence of acidic cations like Aluminum (Al) and Hydrogen (H). In Midwestern soils, Hydrogen (H) is the dominant acidic cation, whereas high levels of Aluminum (Al) are generally found in highly weathered or extremely low pH soils.

Higher base saturation levels often indicate healthier soils with improved nutrient availability and optimal pH levels for crop growth. Conversely, low base saturation suggests a greater presence of acidic cations, which can result in nutrient deficiencies, lower soil pH, and compromised plant health.

The Role of Cation Exchange Capacity (CEC)

CEC represents a soil’s ability to retain and exchange cations, whether basic or acidic. The main factors determining a soil’s CEC include clay content, clay type, and soil organic matter (SOM). Soils with high CEC values (~20+) typically have greater base saturation levels due to their capacity to hold more basic cations. In contrast, highly weathered soils with low CEC (<12) tend to contain higher levels of acidic cations like Al and H.

High CEC soils also exhibit increased buffering capacity, which enables them to resist changes in soil pH and fluctuations in base saturation ratios. Consequently, adjusting soil test nutrient levels and pH in high CEC soils often requires larger applications of fertilizers or lime to achieve noticeable results. See below the chart of what is considered “optimum” soil base saturation levels at each CEC level.

How Does SO4 Pelletized Gypsum Impact Base Saturation?

SO4 Pelletized Gypsum provides a highly soluble and plant-available source of calcium, which can influence base saturation over time. When applied, SO4 can replace sodium (Na) or magnesium (Mg) on soil exchange sites with calcium, increasing Ca base saturation. Raising Ca levels relative to Mg or Na enhances soil structure, increases pore space, and alleviates compaction. However, these improvements occur gradually and require a long-term strategy.

At Calcium Products, we offer SO4 rate calculators to assist growers in amending soils with high sodium levels, often resulting from irrigation water or manure applications. Additionally, our rate recommendation tool helps adjust base saturation levels in soils with excessive magnesium. In cases where lowering Mg levels is necessary, particularly in high CEC soils, SO4 application rates may need to be significantly higher, making them less cost-effective. As an alternative, growers can use SO4 as a sulfur source to allow gradual calcium accumulation over time.

It is also important to recognize that Ca and Mg levels are influenced by a soil’s parent material and clay type, meaning they cannot always be easily altered.

The Role of 98G Pelletized Limestone

The impact of 98G Pelletized Limestone on base saturation is more straightforward. By applying 98G, soil acidity is neutralized, leading to reduced hydrogen (H⁺) concentrations in the soil. Lower H⁺ levels translate to a higher percentage of basic cations (Ca, Mg, K, Na) occupying soil exchange sites, thus increasing base saturation.

Like SO4, 98G contributes calcium to the soil, but since limestone is less soluble than gypsum, the process takes longer to manifest in the form of increased calcium levels on soil exchange sites. Research from Iowa State University illustrates the relationship between soil pH and base saturation levels, reinforcing the role of 98G in improving soil conditions over time.

Conclusion

Soil base saturation is a complex but valuable indicator of a soil’s capacity to supply essential nutrients to crops. While several factors influence base saturation, SO4 and 98G offer effective solutions for improving soil health by increasing calcium levels, raising soil pH, and enhancing nutrient availability. However, these adjustments require time and a consistent approach.

For growers looking to optimize their soil’s base saturation, consulting with a Calcium Products Territory Sales Manager can provide tailored recommendations and strategies for achieving long-term soil health improvements

For more information about 98G Pelletized Limestone or SO4 Pelletized Gypsum, contact your local Territory Sales Manager today!

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