Factors to Consider in Corn Sulfur Application

INSIGHTS

• Responses to sulfur (S) fertilizer can be obtained regardless of planting date.

• In general, hybrids responded similarly to S applications.

• S applications can mitigate weather risks associated with the dynamic nature of plant-available S in the soil.

Trends in Sulfur Availability in Corn

Figure 1. Twenty pounds per acre of sulfur applied at planting (left) compared to none (right) in 2021 trial.

Sulfur deficiencies in corn have become increasingly prevalent in recent years primarily due to some key trends:

1. Reduction in atmospheric S deposition from improved air emission standards: in the last two decades much of the Midwest went from receiving 15-25 lbs/acre/year of S from atmospheric deposition to almost none today.

2. Higher yielding crops require more S: in general, corn will accumulate 0.1 lbs. of S/bushel. Crop demand for S is higher now than it was 5-10 years ago. Over half of the S accumulated by corn is removed by the grain.

3. Earlier planting reduces soil temperature and S mineralization: farmers continue to plant earlier because they have more acres to cover and want to capture yield benefits. High organic matter soils can help maintain adequate soil S levels, as it is mineralized into a plant-available sulfate form. However, soils are typically cooler with early planting and mineralization is slowed, resulting in sulfur deficiencies often observed in early vegetative corn.

Soil tests do not always account for in-season S mineralization, which can make predicting soil sulfur levels challenging.

Graph 1. Yield response to S treatment averaged across 2 hybrids at 17 locations in 2021 and 2023.

Previous Agronomy in Action Sulfur Research Summary

In 2021 and 2023, trials were established at 17 locations across the Midwest to evaluate the effect of S application timing on corn yield. Sulfur was applied at 20 lbs/A either with the planter or sidedressed at the V6 growth stage. Five out of the 17 sites had a significant response to S fertility regardless of application timing (Graph 1).

Planting Date Effect on Sulfur Response

In 2024, the Golden Harvest Agronomy in Action team expanded on previous S trials to evaluate if corn would have a greater response to S applications with earlier planting dates compared to later planting dates.

A trial was conducted with two planting dates at Malta, IL, (4/25/2024 and 5/13/2024) and Slater, IA, (4/12/2024 and 5/15/2024). On each planting date, ammonium thiosulfate (ATS) 12-0-0-26S was planter-applied 2×2×2 at 20 lbs S/A compared to the check, which did not receive any S. The check received 9 lbs N/A as urea ammonium nitrate (UAN) applied 2×2×2 with the planter to balance for N across all treatments.

Yield Results

Graph 2. Effect of planting date and sulfur application on yield averaged across 4 hybrid brands and 2 locations in 2024.

The effect of planting date on yield was significantly different between locations, with the later planting date yielding 18 bu/A less at Malta, IL, and 53 bu/A less at Slater, IA, when averaged across all treatments and hybrids (data not shown). However, the effect of planting date on S response and hybrid was similar for both locations, so all data shown is averaged across both locations.

Graph 3. Effect of sulfur application on yield at the later planting date for 4 hybrids averaged across 2 locations in 2024.

When averaged across all hybrids and locations, 20 lbs/acre of S applied with the planter did not significantly affect yield at either planting date. Sulfur applied at the later planting date tended to increase yields slightly more than earlier planting dates, although neither were statistically significant (Graph 2). The lack of response within the early planting dates may have been caused by warmer spring conditions with high organic matter soils providing sufficient available S to the plants within the trial area.

Graph 4. Effect of planting date on yield for 4 hybrids averaged across 2 locations in 2024.

For the later planting date, statistically there were no differences in hybrids, however, G08U00 brand tended to be less responsive to the S application with only a 1 bu/A increase in yield compared to the other three hybrids, which ranged from 8-11 bu/A (Graph 3). Planting later tended to penalize G08U00 brand more than other hybrids, reducing yield potential by 16% compared to the other three hybrids that only had a 13% reduction in yield potential (Graph 4). However, G08U00 brand had the highest yield potential of all hybrids with the earliest planting date.

Summary

Results from this study highlight the dynamic nature of S availability in corn. Temperature, moisture, organic matter, and soil pH levels all affect plant-available S, making crop needs hard to predict. Even during later planting windows when soils are warmer and likely mineralizing more S, crop demand for S can still exceed what the soil can supply. If S deficiencies are apparent during early vegetative stages, S applications can prevent additional yield loss, but yield potential can never fully recover. Having an S management plan and taking a proactive approach to S fertility is important to mitigate weather risks regardless of planting date.

Figure 2. Corn planted on 4-25-2024 (left) and 5-13-2024 (right) at Malta, IL.