Polysulphate: A Reliable Alternative to Gypsum for Peanut Production

The Growing Need for a Gypsum Alternative

Adaptability is the hallmark of successful growers and the agricultural industry as a whole. Over the years, we’ve learned to navigate shifting weather patterns, fluctuating markets, and more. Now, with the decline in synthetic gypsum supply caused by the transition from coal to natural gas, peanut growers face a new challenge: securing a dependable calcium source. In this landscape, Polysulphate has emerged as a promising alternative. Research trials demonstrate that when applied correctly—particularly in a banded application—Polysulphate can sustain yields even at reduced application rates. Exploring university and on-farm trials conducted between 2020 and 2024 across the southern U.S., we can evaluate and make the case for its effectiveness in peanut production.

Why is There a Gypsum Shortage?

The transition from coal to natural gas in U.S. power plants has reduced the availability of synthetic gypsum, a key calcium source for peanut production.  Gypsum is often produced as a byproduct of coal-fired power plants, where sulfur is scrubbed from emissions. As more plants switch to natural gas, which has lower sulfur content, synthetic gypsum production has declined. This has raised concerns that peanut growers could face gypsum shortages, emphasizing the need to diversify supply sources.

The Importance of Calcium for Peanuts

Calcium is essential for peanuts, particularly during pod formation. Much like a sturdy foundation supports a house, calcium provides the structural strength that peanut pods need to develop properly. Without enough calcium, pods can falter, leading to empty shells (“pops”) or a higher risk of pod rot. To avoid these problems, peanut growers have traditionally relied on gypsum as a primary calcium source. University of Georgia Extension recommends applying 1,000 lbs./acre of gypsum at early bloom if:

• Soil test calcium is below 500 lbs./acre, or
• The calcium-to-potassium ratio is less than 3:1.

Exploring Alternatives to Gypsum

When gypsum is in short supply or costly, growers have a few alternatives —lime, mined gypsum and Polysulphate:

• Lime (Calcium Carbonate): Provides calcium but is less water-soluble than gypsum and raises soil pH. Best applied before planting.
• Mined Gypsum: Naturally occurring gypsum is available but can be expensive due to transportation costs.
• Polysulphate: A natural mineral fertilizer (mined as Polyhalite) provides calcium, magnesium, potassium, and sulfur. Its slow-release properties help meet crop nutrient demands over time. Research has shown Polysulphate performs comparably to gypsum for peanuts, more cost-effectively, often at lower application rates.

Research on Polysulphate vs Gypsum on Peanuts

University Research on Polysulphate

• University of Georgia Trials (2020–2022): Under both dryland and irrigated conditions, Polysulphate produced similar yields to high rates of gypsum.
• Mississippi State University Study (2024): High-calcium soils (>1,600 lbs/A) showed Polysulphate outperforming gypsum in yield and grade when applied via banding at 100 lbs/A of calcium (Figure 1). Broadcast Polysulphate also beat gypsum in yield, but not in grade.

Figure 1. Comparison of Gypsum vs. Polysulphate applied at the same rate of calcium (100 lbs/A) on peanut yield and grade (broadcast vs. banded application).

Grower Strip Trials: Real-World Performance (Figure 2)

In 2024, peanut strip trials were conducted across four Southeastern states:

• Gypsum was applied at 700–1,000 lbs/A.
• Polysulphate was tested at 200 and 400 lbs/A.

Results varied by location due to differences in soil type, rainfall, and fertility. For example, in Georgia, gypsum was applied at 700 lbs/A. These findings reinforce the importance of site-specific recommendations based on soil testing.

Figure 2: Multi-location on-farm peanut strip trial results comparing gypsum at 700- 1000 lbs/A vs Polysulphate at 200 and 400 lbs/A.

Key Findings from Research and Trials – Cost-Effective Results

Across university and grower trials, what we have determined is that Polysulphate often matched or exceeded gypsum’s performance, even at lower application rates. When applied correctly, it provides a reliable and economical calcium source for peanut production. Due to its lower application rates—just 100 to 200 lbs/acre— we can offer growers a competitive alternative to gypsum while enhancing labor and application efficiency.

Additional Benefits of Polysulphate for Growers:

• Flexible Timing: Can be applied pre-plant or at early bloom.
• Lower Application Rates: Saves labor and time.
• Ease of Application: Works with standard fertilizer spreaders, unlike bulkier gypsum.

Conclusion: A Smart Solution for Changing Times

The shift from coal to natural gas has created gypsum supply challenges for peanut growers, but Polysulphate offers a proven and effective solution. It provides key nutrients, performs well in trials, and offers application advantages that save time and labor. With proper soil testing and application, Polysulphate can help growers maintain high yields and quality in changing and challenging times. To learn more about how Polysulphate can support your peanut production, consult your agronomist or reach out to one of our experts. It’s an exciting new chapter in how we approach fertilizer and crop nutrition.

Source: University of Georgia Extension. (2024). Peanut production quick reference guide. University of Georgia Cooperative Extension. https://peanut.ces.uga.edu

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