Soybean Trials: Polysulphate® Sulfur Boosts Yield

As growers continue to seek strategies to improve input efficiency and yield stability, sulfur (S) fertilization has become increasingly important in soybean production. Historically, atmospheric deposition provided adequate background levels of sulfur, but clean air regulations and reduced industrial emissions have significantly decreased sulfur inputs from the atmosphere. As a result, sulfur deficiencies are becoming more common in many agricultural systems, including soybean fields.

To address this emerging nutrient deficiency, a series of trials conducted between 2022 and 2024 by Purdue University and grower collaborators across the Midwest and Southern U.S. evaluated Polysulphate®, a multi-nutrient sulfur fertilizer, against the grower standard ammonium sulfate (AMS). This bulletin summarizes the key findings and offers practical recommendations for soybean producers seeking to improve yield through more effective sulfur management.

Purdue University – Rice, Indiana

The study was a randomized complete block design with 13 treatments, two fertilizer sources (AMS and Polysulphate) applied at three different rates of sulfur at two different times.

Ammonium Sulfate & Polysulphate on Soybean Yield Trial

By: Dr. S. Casteel, Purdue Univ.

Table 1. Shows the list of treatments with source, rate of sulfur and amount of product material. Pre-plant applications in March and pre-emergence in May.

Figure 1: Summary of the average yield of AMS and Polysulphate across rates and timing for 2022 and 2023.
Notes: Sulfur fertilizer source significantly increased soybean yield above the control in 2022 at the 0.10 significance level, but not in 2023

Figure 2: Average yield of the three rates of S across source and timing.

Results:

• Both AMS and Polysulphate significantly increased yield over the untreated control (UTC).
• In 2022, sulfur application led to statistically significant yield increases at the 0.10 significance level; however, this was not the case in 2023.
• While no significant yield differences were detected among sulfur sources, rates, or timing, trends consistently supported the efficacy of Polysulphate.

Grower Strip Trial Southeast Arkansas 

This was a split field trial. Half the field was treated with grower standard and the other with Polysulphate. A grower-managed strip trial compared:

• AMS at 100 lbs/A
• Polysulphate at 100 lbs/A

Ammonium Sulfate & Polysulphate on Soybean Yield

Grower Trial, Southeast Arkansas

Figure 3: Polysulphate and AMS applied to soybean in Southeast AR

Results:

• Both treatments produced identical yields of 74 bu/A.
• However, the grower observed higher residual sulfur in the Polysulphate-treated area post-harvest, suggesting a more sustained release of nutrients.

Agri-Tech Consulting, 2024 Whitewater, WI 

In a 2024 replicated trial:

• Grower standard (no sulfur)
• Polysulphate at 100 lbs/A

Ammonium Sulfate & Polysulphate on Soybean Yield

Trial By: Agri-Tech Consulting, Whitewater, WI

Figure 5: Polysulphate applied as a sulfur source to soybean in Whitewater, WI

Results:

• Polysulphate outperformed the GSP, which included no sulfur input.
• Yield increased by 7.5 bu/A, and differences were significant at the 0.10 level.

This emphasizes the importance of sulfur fertilization in high-yield soybean systems.

Conclusion

The combined trial results show that Polysulphate matches or exceeds the performance of AMS in soybean production. Both sources improved yield over the untreated control, affirming the need for sulfur fertilization in today’s soybean systems.

However, Polysulphate offers several additional agronomic and environmental advantages. Unlike AMS, which contributes to long-term soil acidification due to its ammonium content, Polysulphate provides sulfur without acidifying the soil, making it a more sustainable option, particularly for low-buffering or already acidic soils. In addition, Polysulphate delivers a broader nutrient package—including potassium, calcium, and magnesium—and features a slower, more sustained nutrient release profile that may improve nutrient uptake efficiency and reduce leaching risk.

Growers looking to improve sulfur management in soybeans should consider a 1:1 comparison with Polysulphate at your standard sulfur rate. The multi-nutrient value and soil-friendly chemistry may give you an edge in yield and sustainability.