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Sulfur Fertilizer in Wheat: Is It a Have-To?
Brian Arnall, Precision Nutrient Management Extension Specialist.
Sulfur has become a much bigger part of the fertility conversation over the last several years, and for good reason. We are producing higher-yielding crops, removing more nutrients from our fields, and receiving less sulfur from atmospheric deposition than we did several decades ago. But that does not mean sulfur fertilizer has become a “have-to” application for every wheat field.
Ms. Kelby Linn’s research provides a good example of why soil testing still matters. Across the environments in this study, sulfur fertilizer did not increase wheat grain yield. The soil was able to supply enough sulfur to meet the yield demand of the crop. When fertilizer margins are tight, that is important. Applying a nutrient that is already present in sufficient amounts is an expense without a yield return. At the same time, these results should not be interpreted to mean that sulfur fertilizer is unnecessary. Sulfur management is ultimately a mass-balance issue. Every bushel we harvest removes nutrients from the field. As yields increase, nutrient removal increases. If we continually remove more sulfur than the soil and other sources can supply, at some point we have to replace it.
That is why I am more concerned about sulfur in intensive, high-yield production systems, particularly on sandier soils and soils with lower organic matter. These soils generally have less capacity to supply sulfur, while a high-yielding crop is removing more of it. That combination increases the likelihood of sulfur becoming limiting. This is where soil testing becomes a valuable management tool. Rather than treating sulfur as something wheat either “always needs” or “never needs,” we should identify the fields where soil supply is unlikely to meet crop demand and put our fertilizer dollars there.
It is also important not to carry the wheat results presented here across every cropping system. Our ongoing work in corn has shown more response to sulfur fertilizer than we have observed in wheat. That fits the larger nutrient-removal discussion, particularly as we push corn yields higher. We will share two years of data after this year’s corn harvest.
Kelby’s research also raises another interesting question. If the soil already contains enough sulfur to maximize wheat grain yield, does additional sulfur do anything? His work suggests that it can. The response may not be additional bushels, but changes in how nitrogen is used and, ultimately, the quality and functionality of the grain.
Understanding Sulfur’s Role Beyond Grain Yield
Kelby Linn and Brian Arnall
Why Nitrogen and Sulfur Must Work Together
Nitrogen (N) has long been recognized as the most important nutrient for winter wheat production. It is a primary driver of vegetative growth, grain yield, and grain protein concentration, making N management the focus of most wheat fertility programs across Oklahoma. Sulfur (S) plays a different but complementary role. Nitrogen supplies the building blocks needed to produce proteins, while S is needed to form sulfur-containing amino acids such as cysteine and methionine. These amino acids contribute to the bonds that strengthen gluten proteins and influence dough strength, elasticity, and overall baking performance. When S becomes limiting, wheat may continue to take up N but may be less efficient at incorporating that N into functional storage proteins. Therefore, the relationship between N and S may become increasingly important as N rates and yield potential increase. The literature suggest that relationship can be wrong in both directions were N is in excess and S is deficient can cause yield loss but also where S is in excess and N is deficient we can experience loss.
Understanding the System
To better understand how S behaves under different N environments, field trials were conducted across north-central Oklahoma and south-central Kansas during the 2023–2025 growing seasons. The objective was to determine whether S responses differed when N was limiting compared with a high-N production environment.
Two N fertilizer rates were evaluated using ammonium sulfate (AMS) and urea:
- 60 lb N/ac, representing a sub-optimal or N-limited environment
- 140 lb N/ac, representing a high-N environment where S could have greater potential to become limiting
Each N rate was combined with five S rates supplied as AMS: 0, 5, 10, 20, and 30 lb S/ac.
Sulfur was applied before jointing, between Feekes 4 and 6, with the top-dresss N application, when wheat nutrient uptake is increasing and the crop is transitioning toward reproductive development. This allowed us to evaluate the influence of S on grain production, N utilization, and grain quality under both N-limited and high-N conditions.
Soil testing was an important part of interpreting the results. Across the locations, sulfate-S was present in the soil profile before fertilizer application. Soil test S varied among sites and depths, reinforcing that the amount of S already available to the crop can differ considerably among fields.
Table 1. Average composite soil sample results of pH, organic matter (OM), nitrate, and SO4 for all locations of the S interaction study.
First, What Happened to Yield?
Nitrogen remained the dominant factor controlling grain yield. Across environments, average wheat yield increased from 46 bu/ac with the lower N rate to 56 bu/ac with the higher N rate. Sulfur, however, did not significantly increase grain yield. Soil tests indicated that the sites generally contained measurable sulfate-S, which correctly predicted the lack of a yield response. If grain yield had been our only measurement, the story could have ended there. But the addition of S affected several characteristics related to how the grain performed during milling and dough development, particularly under the high-N treatment.
Why Wheat Quality Matters
Most Oklahoma wheat producers market wheat based primarily on grain yield and protein concentration. Once wheat moves farther through the grain chain, however, millers and commercial bakeries evaluate additional characteristics that determine how the flour performs. Hard red winter wheat is valued for its ability to produce strong bread flour. That ability depends not only on the amount of protein in the grain but also on the structure and functionality of those proteins. Nitrogen applications generally increases grain protein concentration, while S can influence the composition of those proteins. Adequate S promotes the formation of S-containing proteins involved in strong gluten networks. As a result, two wheat samples with similar protein concentrations can potentially behave differently during milling and baking.
Looking Beyond Grain Protein
Several measurements were used to evaluate wheat and flour quality. Grain protein represents the total protein concentration of the kernel and remains an important factor in wheat marketing. Flour protein measures the protein concentration after the bran and other components have been removed during milling. Other measurements tell us more about milling and baking performance. Milling yield describes how much usable flour can be produced from the grain, while flour ash is an indicator of the amount of mineral material remaining in the flour and can help evaluate milling efficiency. Falling number provides information about alpha-amylase activity and potential preharvest sprouting. Gluten index is particularly useful for evaluating gluten strength. A higher gluten index generally indicates stronger gluten that can better maintain dough structure during mixing and fermentation.
What Happened When We Made Dough?
One of the unique aspects of this study was evaluating flour with DoughLAB analysis. Rather than measuring only grain or flour composition, DoughLAB measures how flour behaves during mixing. Development time measures how long the dough must be mixed to reach optimum consistency. Dough stability measures how long the dough maintains that consistency before beginning to break down. Mixing tolerance index, or MTI, measures how rapidly the dough weakens after optimum development. Water absorption measures the amount of water required to produce dough at a standard consistency.
Of these measurements, dough stability provided one of the more interesting S responses. Under the high-N treatment, average dough stability increased from approximately 6 minutes without S to nearly 15 minutes at the highest S rate. Greater dough stability indicates that the gluten network was able to withstand mixing for a longer period before breaking down. For commercial baking, this can be important because stronger, more stable dough generally provides greater tolerance during mixing and more consistent performance during processing.
What Did We Learn?
Across these environments, N remained the primary factor controlling grain yield. Increasing N increased average yield, while adding S did not provide a significant yield response. However, the absence of a yield response did not mean S had no effect on the wheat. Under high-N conditions, S improved several measurements associated with grain and dough functionality, including gluten strength, dough development, and dough stability.
These results help separate two questions that are sometimes treated as the same question: Does the crop need S to produce more grain, and does S influence what happens inside the grain?
At the locations included in this study, the answer to the first question was no. The soils supplied enough S that additional fertilizer did not increase yield. The second question was more complicated. Sulfur influenced characteristics associated with protein functionality and end-use quality, particularly when N supply was high. That does not mean S should be applied routinely to improve wheat quality. For producers, the first fertilizer decision should still be based on whether the crop is likely to become S deficient. Soil testing, soil texture, organic matter, yield potential, and production history all provide information that can help make that decision. The larger lesson from this work is that S has a role in wheat beyond simply producing more bushels. Understanding that role helps us make better fertilizer decisions while continuing to put fertilizer where it is most likely to provide a return.
Data drawn from The Influence of Sulfur Under Nitrogen Extremes in Winter Wheat.
Linn, Kelby DeeAnn. Oklahoma State University ProQuest Dissertations & Theses, 2026. 32668685.
One Well-Timed Shot: Rethinking Split Nitrogen Applications in Wheat production
Brian Arnall, Precision Nutrient Management Specialist
Samson Abiola, PNM Ph.D. Student.
Nitrogen is the most yield limiting nutrient in wheat production, but it’s also the most unpredictable. Apply it too early, and you risk losing it to leaching or volatilization before your crop can use it. Apply it too late, and your wheat has already determined its yield potential; you’re just feeding protein at that point. For decades, the conventional wisdom has been to split nitrogen applications: put some down early to get the crop going, then come back later to apply again. But does splitting actually work? And more importantly, when is the optimal window to apply nitrogen if you want to maximize both yield and protein quality? We spent three years across different Oklahoma locations testing every timing scenario to answer these questions.
How We Tested Every Nitrogen Timing Scenario in Oklahoma Wheat
Between 2018 to 2021, we conducted field trials at three Oklahoma locations, including Perkins, Lake Carl Blackwell, and Chickasha, representing different soil types and growing conditions across the state. We tested three nitrogen rates: 0, 90, and 180 lbs N/ac, applied as urea at five critical growth stages based on growing degree days (GDD). These timings were 0 GDD (preplant, before green-up), 30 GDD (early tillering), 60 GDD (active tillering), 90 GDD (late tillering, approximately Feekes 5-6), and 120 GDD (stem elongation, approaching jointing). We also compared single applications at each timing against split applications, where half the nitrogen (45 lbs N ac-1) went down preplant, and the other half was applied in-season (45 lbs N ac-1).
The Sweet Spot: Yield and Protein at the 90 lbs N/ac Rate
Across all site-years, at the 90 lbs N/ac rate, timing had a significant impact on both yield and protein. The highest yields came from the 30 and 90 GDD timings, producing 62 to 66 bu/ac, with 60 GDD reaching the peak (Figure 1). Protein at these early timings stayed relatively modest at 13%. The 90 GDD timing delivered 62 bu/ac with 14% protein matching the yield of the 30 GDD application but pushing protein a percentage higher (Figure 2). The real problem appeared at 120 GDD. Delaying application until stem elongation dropped yields to just 49 bu/ac, even though protein climbed to 15%. That’s a 13 bushel penalty compared to the 90 GDD timing. At current wheat prices per bushel, that late application may cost farmers over $100 per acre in lost revenue. By 120 GDD, the crop has already determined its yield potential tillers are set, head numbers are locked in and nitrogen applied at this stage can only be directed toward protein synthesis, not building more yield components.
More Nitrogen Does not lead to high yield
Doubling the nitrogen rate to 180 lbs N/ac revealed something critical, more nitrogen doesn’t mean more yield. The yield pattern remained nearly identical to the 90 lbs N/ac rate. The 60 GDD timing produced the highest yield at 68 bu/ac, followed closely by 30 GDD at 67 bu/ac. The 90 GDD timing yielded 62 bu/ac, and the 120 GDD timing again crashed to 51 bu/ac. The only difference between the two rates was protein concentration (Figure 2). At 180 lbs N/ac, protein levels increased across all timings: 13% at preplant, 15% at both 30 and 60 GDD, 15-16% at 90 GDD, and 16% at 120 GDD. This confirms a fundamental principle: once farmers supply enough nitrogen to maximize yield potential, which occurred at 90 lbs N/ac in these trials, additional nitrogen only increases grain protein. It does not build more bushels. Unless farmers are receiving premium payments for high-protein wheat, that extra 90 lbs of nitrogen represents a cost with no yield return.
Should farmers split their nitrogen application?
Now that timing has been established as critical, the next question becomes: should farmers split their nitrogen applications, or is a single application sufficient? The conventional recommendation has been to split nitrogen apply part preplant to support early growth and tillering, then return with a second application later in the season to boost protein and finish the crop. But does the data support this practice? We compared three strategies at each timing: applying all nitrogen preplant, applying all nitrogen in-season at the target timing, or splitting nitrogen equally between preplant and in-season timing. The goal was to determine whether the extra trip across the field will deliver better results.
Our findings revealed that splitting provided no consistent advantage. At 30 GDD, all three strategies preplant, in-season, and split performed identically, producing 62-65 bu/ac with 12-13% protein (Figure 3 and 4). No statistical differences existed among them. At 60 GDD, similar pattern was held. Yields ranged from 61 to 66 bu/ac and protein stayed at 12-13% regardless of whether farmers applied all nitrogen preplant, all at 60 GDD, or split between the two. At 90 GDD, the single in-season application actually outperformed the split. While yields remained similar across all three methods (61-64 bu/ac), the in-season application delivered significantly higher protein at 13.7% compared to 12.4% for preplant and 12.5% for split applications. This suggests that concentrating nitrogen at 90 GDD, rather than diluting it across two applications, allows more efficient incorporation into grain protein. The only timing where splits appeared beneficial was 120 GDD, where the split application yielded 59 bu/ac compared to 51 bu/ac for the single late application. But this is not a win for splitting, it simply demonstrates that applying all nitrogen at 120 GDD is too late and putting half down earlier salvages some of the yield loss. Across all timings tested, splitting nitrogen into two applications offered no agronomic advantage over a single well-timed application, meaning farmers are making an extra pass for no gain in yield or protein.
Practical Recommendations for Nitrogen Management
Based on three years of field data, farmers should target the 90 GDD timing (late tillering, Feekes 5-6) for their main nitrogen application to achieve the best balance between yield and protein. This window typically falls in late February to early March in Oklahoma, though farmers should monitor crop development rather than relying solely on the calendar apply when wheat shows multiple tillers, good green color, and vigorous growth. A rate of 90 lbs N/ac maximized yield in these trials; higher rates only increased protein without adding bushels, so farmers should only exceed this rate if receiving premium payments for high-protein wheat. Splitting nitrogen applications provided no advantage at any timing, meaning a single well-timed application at 90 GDD is sufficient for most Oklahoma wheat production systems. The exception would be sandy soils with high leaching potential, where splitting may reduce nitrogen loss. Farmers should avoid delaying applications until 120 GDD or later, as this timing consistently resulted in 15-25 bushel per acre yield losses even though protein increased. For farmers specifically targeting premium protein markets, a two-step strategy works best: apply 90 lbs N/ac at 90 GDD to establish yield potential and baseline protein, then follow with a foliar application of 20-30 lbs N/ac at flowering to push protein above 14% without sacrificing yield. Finally, weather conditions matter hot, dry forecasts increase volatilization risk and reduce uptake efficiency, so farmers should consider moving applications earlier if low humidity conditions are expected.
Split Application Caveat * Note from Arnall.
The caveat to the it only takes one pass, is high yielding >85+ bpa, environments. In these situation I still have not found any value for preplant nitrogen application. I have seen however a split spring application is valuable. Basically putting on 30-50 lbs at green-up, with the rest following at jointing (hollowstem). The method tends to reduce lodging in the high yielding environments.
This work was published in Front Plant Sci. 2025 Nov 6;16:1698494. doi: 10.3389/fpls.2025.1698494
Split nitrogen applications provide no benefit over a single well timed application in rainfed winter wheat
Another reason to N-Rich Strip.
Yet just one more data set showing the value of in-season nitrogen and why the N-Rich Strip concept works so well.
Questions or comments please feel free to reach out.
Brian Arnall b.arnall@okstate.edu
Acknowledgements:
Oklahoma Wheat Commission and Oklahoma Fertilizer Checkoff for Funding.
Nitrogen and Sulfur in Wheat
Brian Arnall, Precision Nutrient Management Specialist
Samson Abiola, PNM Ph.D. Student.
Nitrogen timing in wheat production is not a new topic on this blog, in-fact its the majority. But not often do we dive into the application of sulfur. And as it is top-dressing season I thought it would be a great opportunity to look at summary of a project I have been running since the fall of 2017 which the team has call the Protein Progression Study. The objective was to evaluate the impact of N and S application timings on winter wheat grain yield and protein. With a goal of looking at the ratio of the N split along with the addition of S and late season N and S, in such a way that we could determine BMP for maximizing grain yield and protein.
My work in the past has shown two things consistently, that spring N is better on the average and S responses have been limited to deep sandy soils in wet years. Way back when (2013) on farm response strips showed high residual N at depth and no response to S. https://osunpk.com/2013/06/28/response-to-npks-strips-across-oklahoma/. But there has been a lot of grain grown since that time expectations are that we should/are seeing an increase in S response. In fact Kansas State is seeing more S response, especially in the well drained soils in east half of the state.
Some KSU Sulfur works.
https://www.ksre.k-state.edu/news/stories/2022/04/video-sulfur-deficiency-in-wheat.html
https://eupdate.agronomy.ksu.edu/article/sulfur-deficiency-in-wheat-364-1
Click to access sulphur-in-kansas-plant-soil-and-fertilizer-considerations_MF2264.pdf
So the Protein Progression Project was established in 2017 and where ever we had space we would drop in the study. So in the end across six seasons we had 13 trials spread over five locations. Site-years varied by location: Chickasha (2018-2022), Lake Carl Blackwell (2018-2023), Ballagh (2020), Perkins (2021), and Caldwell (2021).
First lets just dive into the the N application were we looked at 100% pre vs 50-50 split and 25-75 split (Table 2.) Based upon the wealth of previous work https://osunpk.com/2022/08/26/impact-of-nitrogen-timing-2021-22-version/, its not much of a surprise that split application out preformed preplant and that having the majority applied in-season tended to better grain yields and protein values.
This next table is were things get to be un-expected. While the data below is presented by location, we did run each site year by itself. In no one site year did S statistically, or numerically increase yield. As you can see in Table 2 below, the only statistical response was a negative yield response to S. And you can not ignore the trend that numerically, adding S had consistently lower yields. Even more surprising was the same trend was seen in Protein.
One aspect of Protein Progression trials were that while 0-6″ soil test S tended to be low. We would often find pretty high levels of S when we sampled deeper, especially when there was a clay increase with depth. Sulfur tends to be held by the clay in our subsoil. We are also looking at better understanding the relationship between N and S. In fact a review article published in 2010 discussed that the N and S ratio can negative influence crop production when either one of the elements becomes un-balanced. For example we are seeing more often in corn that when N is over applied we can experience yield loss, unless we apply S. Meaning at 200 lbs of N we make 275 BPA, at 300 N lbs we make 250, but 300 N plus 20 S we can make 275 again. Part of the rationale is that excessive N limits S mineralization. On the flip side if S is applied while N is deficient and yield decrease could be experienced. Maybe that is what we are seeing in this date. Either way, this data is why the Precision Nutrient Management program is spending a fair amount of efforts in understanding the N x S relationship in wheat (which we are looking at milling quality also) and corn.
A quick dive into increasing protein with late N applications. At three of the five location GPC was significantly increased with Late N. In most cases the anthesis (flowering) application was the highest with exception of Caldwell. We will have another blog coming out in a month that digs into anthesis applied N at a much deeper level, looking at source, nozzle and droplet sizes.
Looking at this study in a vacuum we can say that it probably best to split apply your N and that in central and northern Ok the addition of S in rainfed wheat doesn’t offer great ROI. If I look at the whole picture of all my work and experience I would offer this. For grain only wheat, the majority if not all N should be applied in-season sometime between green up and two weeks after hollow stem. I have had positive yield responses to S applied top-dress, but it has always been deep sandy soils and wet seasons. I have not have much is any response to S in heavier soil, especially if there is a clay increase in the two feet of profile. So my general S recommendation is 10 lbs in sandy soils and if you show low soil test S in heavier ground and you are trying to push grain yields, then you could consider the addition of S as a potential insurance. That said, I haven’t seen much proof of it.
Take Homes
* Split application of nitrogen resulted in higher grain yields and protein concentrations when compared to 100% preplant.
* Putting on 75% of the total N in-season tended to result in higher grain yields and protein concentrations when compared to 50-50 split.
* Adding 10 lbs of S topdress did not result in any increase in grain yield or protein.
A big Thanks to the collaborators providing on-farm locations for this project. Ballagh Family Farms, Turek Family Farms and Tyler Knight.
Citation. Jamal, A.,*, Y. Moon, M. Abdin. 2010 Review article. Sulphur -a general overview and interaction with nitrogen. AJCS 4(7):523-529 (2010). ISSN:1835-2707.
Any questions or comments feel free to contact me. b.arnall@okstate.edu
Down and Dirty with NPK 