Figure 1. Twenty pounds per A of sulfur applied at planting (left) compared to none (right) at Slater, IA in 2023.On average, sulfur (S) applications significantly increased yield regardless of application timing.
Over two years, 5 out of 17 sites had a significant response to S fertility.
In general, hybrids respond similarly to S applications.
Soil organic matter or S soil test values are not great predictors of corn response to S.
Introduction
The occurrence of sulfur deficiency in corn has increased in recent years, largely due to reductions in atmospheric deposition from air emission standard improvements. High organic matter (OM) soils can also help maintain adequate soil sulfur levels as it is mineralized into a plant-available sulfate form. Predicting plant-available soil sulfur levels can be challenging due to delayed mineralization with cooler temperatures. Insufficient spring soil sulfur levels will often reach a sufficient level from mineralization prior to reaching peak demand after pollination. Once mineralized, the sulfate form can also be leached out of rooting zones following periods of excessive rainfall. Soil tests can be used to evaluate soil sulfur levels but may not always account for in-season mineralization or other sources of sulfur such as irrigation water.
2023 Sulfur on Corn Trials
In 2023, sulfur Agronomy in Action trials were established at 9 locations throughout the Midwest. In addition to understanding frequency of response to sulfur, the trials were designed to evaluate application timing and hybrid response differences. Two hybrids, either G06A27 and G06B57 brand or G14B32 and G15J91 brand, were planted at each location to better understand response differences among hybrids.
Sulfur treatments were applied as either at-planting or V6 timings in separate plots and compared against a non-sulfur treatment. Sulfur applied at the time of planting was surface dribbled 3-inches to each side of the row behind the closing wheel of the planter. Applications at V6 growth stage were applied in a band at the base of the plant on both sides of each row. Ammonium thiosulfate (ATS) 12-0-0-26S, a form of sulfur that is easily applied in a liquid form, was applied at 20 lbs/A of S, which simultaneously provided 9 lbs/A of nitrogen at each timing. All plots not receiving sulfur at planting were treated with 9 lbs/A of N in the form of urea ammonium nitrate (UAN) at the same timing. UAN was also applied to all treatments at the V6 timing at a rate that provided an equivalent 50 lbs/A of total nitrogen to all treatments. Every plot received a balanced total of 59 lbs/A of nitrogen via the two timings so that nitrogen within ATS did not bias results.
Treatments were replicated 6 times in a split-plot design at each trial site. This trial was first conducted at 8 locations in 2021 and was repeated in 2023 to better understand the environment by sulfur response interaction.
Table 1. Effect of sulfur treatment on yield at 9 locations averaged across two hybrids in 2023. Corn Yield Response to Sulfur
On average, across all locations and hybrids, yield significantly increased by 6 bu/A when 20 lbs/A of S was applied at V6 and 5 bu/A when applied at planting (Table 1).
Three of the nine 2023 locations showed a significant response to sulfur fertilizer. At Bridgewater, SD, 20 lbs/A of S increased yield by 14 bu/A regardless of application timing. At Janesville, WI there was 13 bu/A response to S applied at V6 and a 16 bu/A response when applied at planting. The V6 application of S significantly increased yield by 11 bu/A at Slater, IA.
Statistically, hybrids responded similarly to S applications. At the late relative maturity locations, G14B32 and G15J91 both significantly increased yield with S applied at V6 by 7 and 6 bu/A, respectively (Graph 1). G14B32 tended to have a greater response to S applied at planting than G15J91. At the early relative maturity locations, both hybrids significantly increased yield with both S application timings. G06A27 tended to respond better to S applied at planting while G06B57 had a similar response to both application timings (Graph 1).
*significant difference between sulfur treatment and the check at α = 0.10 Graph 1. Effect of sulfur treatment on yield averaged across locations in 2023 Muti-year Sulfur Response Results
The yield response to S applications varied across the 17 site-years (8 in 2021 and 9 in 2023). Two locations in 2021 and three locations in 2023 had a significant response to S fertilizer (Graph 2). Across both years, corn grown at Geneseo, IL in 2021 had the greatest response to S increasing yield by 39 bu/A when applied at planting and 20 bu/A when applied at V6. When averaged across location and hybrids, there was a 5 bu/A response when 20 lbs/A of S was applied at planting and 6 bu/A response when applied at V6.
Pre-plant soil tests were taken at most locations to determine if S soil test values can be used as an indication whether a field will be responsive to S applications.
Corn yield response to sulfur fertilizer was not correlated (R2=0.113) with pre-plant S soil test values (Graph 3). The lowest S soil test value was 5 ppm at Geneseo in 2021 as well as Grundy Center and Clinton in 2023. Those three locations showed a 29, 3, and 4 bu/A response to S fertilizer. Sac City and Slater in 2021 had S soil test values of 23 and 15 ppm but experienced a 6 and 17 bu/A response to S applications, respectively. Corn yield response was also not correlated (R2=0.003) with soil organic matter (data not shown).
significant difference between sulfur treatment and the check at α = 0.10 Graph 2. Yield response to sulfur treatment averaged across 2 hybrids at 17 locations in 2021 and 2023. Summary
Graph 3. Correlation between sulfur soil test value and yield response to sulfur application.Sulfur availability and plant uptake is a dynamic process that is highly dependent on environment. There is not just one factor that is responsible for the probability of corn response to sulfur fertilizer. The occurrence of sulfur deficiency in corn has increased in recent years and the detrimental effect on yields are significant. If deficiency symptoms are visual, yield potential has decreased. An in-season application of S fertilizer can stop additional yield loss, but any lost yield potential can never be recovered. These trials show that at planting applications of sulfur can also be advantageous but may be more vulnerable to leaching loss in some years. This trial did not evaluate sulfur rate response, but it is important to consider that reduced rates needed for in-furrow application may not be as responsive as surface dribbled rates used in this trial. It is important to be proactive in S fertility management to mitigate weather risks when S may not mineralize or become available during periods of cool and dry conditions. Sulfur should be considered a critical component to any fertility program to maximize yield potential.
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