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Sulfur Application Timing Effect on Corn Response

Categories: GROWING, CORN
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  • Supplemental sulfur was beneficial to grain yield potential with both application timings at 2 of 8 trial sites.

  • Yield responses from sulfur application almost doubled when applied at planting compared to V6 applications when soil test levels were extremely low.

  • Differences in hybrid response are likely only to occur when sulfur is extremely deficient in soils.

Figure 3. Sulfur application timing trial at Geneseo, IL in 2021
Figure 1. 20 lbs./A of S applied at planting (left) compared to none (right)

Introduction

The occurrence of sulfur (S) 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 S levels can be challenging due to delayed mineralization with cooler temperatures. Insufficient spring soil S 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 S levels, but they may not always account for in-season mineralization or other sources of S, such as irrigation water.

2021 Corn Sulfur Trials

Sulfur response trials were established at 9 Golden Harvest® Agronomy in Action locations across IL, IA, KS, SD and NE in 2021. In addition to understanding frequency of response to S, the trials were designed to evaluate application timing and hybrid response differences. 2 hybrids, G10D21 and G10L16, were planted at each location to better understand response differences among hybrids. S treatments were applied at planting and V6 timings in separate plots and compared against a non-S treatment. S applied at the time of planting was surface dribbled 3 in. 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) 12­0-0-26S, a form of S that is easily applied in a liquid form, was applied at 20 lbs./A, which simultaneously provided 9 lbs./A of nitrogen (N) 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 total of 59 lbs./A of N via the 2 timings so that N within ATS did not bias results.

Treatments were replicated 4 times in a randomized complete block design at each trial site. Leaf tissue samples were collected from the ear leaves of all plots and evaluated for S content at the R1 growth stage. Plots were harvested using a research combine to assess grain yield and moisture.

Table 1. Individual location response to S application at planting or at V6 * = significant p < 0.05 **= significant p < 0.10
Table 1. Individual location response to sulfur application at-planting or at V6
* = significant p < 0.05
**= significant p < 0.10

Corn Yield Response to Sulfur

Yield response to S ranged from 0-38 bu/A across the 2021 trial locations. Of the 7 trials harvested, the Geneseo, IL, and Slater, IA, plots responded significantly more than other locations (Table 1). Both at-planting and V6 application timings responded similarly at Slater with 16.6 and 17.2 bu/A respectively, although little to no deficiency symptoms were present at the site. Deficiency symptoms were noticeable in non-S treatments throughout most of the spring at Geneseo, which had the lowest soil S test values of all sites.

S deficiency symptoms were not visible in corn emerging from treatments that received S at planting, whereas treatments delayed until V6 timing showed symptomology for several weeks following the layby applications at Geneseo. Although there was a 20 bu/A response to the V6 sulfur application at Geneseo, there was an incremental 18.5 bu/A (38.7 bu/A total) gained when applications were applied at time of planting. Although the largest yield response at Geneseo was observed with at-planting applications, R1 ear leaf tissue tests indicated higher concentrations of S in plots treated at V6 timing. This may be in part from a reduction in yield components (kernels per row and rows per ear) that were being determined at V5-V8 growth stages while still under stress. This likely reduced the ability to use up available S throughout grain fill, resulting in higher concentrations remaining in the ear leaf than the at-planting applications.

Figure 2. Trial sites in 2021 and average sulfur response
Figure 2. Trial sites in 2021 and average S response
Figure 2. Trial sites in 2021 and average sulfur response
Graph 1. Hybrid response to S application timing at responsive sites

Hybrid Response to Sulfur

At the Slater trial, hybrids responded similarly to S applications with yield increases ranging from 5.5-7% across the 2 hybrids (Graph 1). At Geneseo, the V6 application timings improved G10D21 yields by 12% whereas G10L16 appeared to be less responsive to the same application timing with only a 5% yield increase. Early application timings increased G10L16 by 14.6%. However, G10D21 again appeared more responsive with a 19.3% yield increase from at planting applications. As both hybrids yielded similarly within specific S application timings at both locations, it would suggest that G10D21 is slightly more sensitive to S deficiency than G10L16 when S is extremely limiting as it was at Geneseo.

In a drought, just as there is increased variability in yield potential, there is also increased soil variability across a field. The different landscape positions, water-holding capacity, nutrient uptake and mineralization will vary across a field, resulting in extreme nutrient concentrations. Often soil test values in dry conditions can seem out of the ordinary or may have samples that are outliers compared to the rest of the field. To combat this, consider increasing the density of soil samples collected in a field following a drought. It may also be beneficial to compare to previous soil sample results. Patterns of results from normal precipitation years compared to sample results from dry years can show trends and help make accurate fertility recommendations.

Graph 2. Relationship between early soil and R1 tissue sampling S test results
Graph 2. Relationship between early soil and R1 tissue sampling S test results

Drivers for Site Responsiveness

Soil and R1 tissue samples from plots not receiving S applications were compared across locations to better understand the lack of responsiveness at sites other than Geneseo and Slater in 2021. Soil tests taken at planting provide a snapshot into plant-available S at that point in time, but they are unable to reflect S that may become available later in the season from sources such as OM mineralization or irrigation water. Normally tissue testing would occur with small plants to allow time to take corrective measures, although in this trial they were taken at R1 to gauge if other sources of S may have mitigated early soil deficiencies. Graph 2 illustrates the relationship of early soil test levels and the R1 tissue test results. Very low soil S levels (5 ppm) and lower soil OM content increased odds of seeing responsiveness at Geneseo. Soils with S levels greater than 10 ppm have historically been considered non-responsive, although Slater had soil levels of 15 ppm and resulted in a significant response. Both the Seward, NE, and Clay Center, KS, sites also had lower soil S levels but had higher leaf tissue test values later in the season and were non-responsive. This may have been in part due to in-season S being partially supplemented through irrigation well water. University of Nebraska irrigation well water surveys found a median value of 35.1 pounds S per acre foot of water sampled, which could have been enough to supplement soil deficiencies.1 The Bridgewater, SD, Keystone, IA, and Sac City, IA, locations all had initial soil S levels greater than 20 ppm and soil OM levels greater than 3.5%, greatly reducing chances of responsiveness. In addition, the Sac City location has a long history of manure application, which can contribute to higher amounts of in-season S mineralization. Like yield, S R1 tissue test levels did not increase with either application timing at Clinton, IL. Potentially excessive sulfate leaching occurred at Clinton from multiple periods of excessive rain early in the season, reducing effectiveness of S applications.

Figure 2. Trial sites in 2021 and average sulfur response
Figure 3. S application timing trial at Geneseo, IL in 2021

Summary

S deficiency is becoming more common in corn production today. As environmental emissions of S continue to be cleaned up, mitigating S deficiency will become increasingly more important. The extremely complex nature of plant-available S is influenced by temperature, moisture, OM and soil pH levels, which will continue to make economic S application decisions difficult in the future. Due to similar sulfate and nitrate behaviors in the soil, management strategies such as application timings will need to be similar. Soil and plant tissue sampling can help identify when S may be deficient and identify where economic responses are more likely to occur.

To learn more about our 2021 trial on sulfur deficiency in corn, watch this video.

References
1 The Nebraska Water Quality Survey, EC 65-165 by Culbertson, Fischbach, et al.

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