There is increasing interest in applying sulfur ahead of crops to increase yield. It is commonly known that the conversion of nutrients from one form to another in the soil can create acidity. Most common sources of sulfur can result in greater acidification of the soil profile which can have a negative impact on soybean over time. For example, it is reported that 5.4 lbs of calcium carbonate is needed to neutralize the acidity produced through the nitrification of 1 lb on N contained in ammonium sulfate. In addition, 3 lbs of calcium carbonate are needed to neutralize the acidity produced through the oxidation of 1 lb of S as elemental sulfur. Other nitrogen sources such as anhydrous ammonium, urea, and P fertilizer sources such as MAP and DAP can also produce acidity. I am increasingly finding surface soil pH less than 6.0 which is considered optimal for corn and soybean production. With more sulfur being applied, are soybean growers creating issues where surface soil pH is decreasing more rapidly resulting in the potential for lost yield?

Limestone is used to correct soil acidity, but limestone is not always easily available or cost effective to apply for some soybean growers. Pelletized lime (pell-lime) is available at a higher cost, and it can be mixed with granular fertilizer. Other soil fertility researchers and I have discussed whether correcting the acidity in a smaller area of the soil, such as a band of fertilizer, may be sufficient for most crops to maximize nutrient uptake. With RTK guidance being more common it is relatively easy to band lower rates of nutrients and then plant over top the bands so newly emerging roots have each access to the nutrients applied and not all the soil need be fertilized. While a fertilizer band may be mixed with more aggressive tillage, repeated application in the same area could give a more optimal zone for nutrient uptake for crops that over time may increase yield with repeated applications. I have also received some comments from crop consultants on the benefits to banding sulfur. Combining the pell-lime with a band application of fertilizer could slow soil acidification reducing the needs for high rates of crushed limestone creating a zone where nutrient availability is increased. The research needs to be assessed over several years as the change in soil pH is not rapid and may take some time before benefits can be achieved. Since it is most common for sulfur as well as other forms of fertilizer to be applied ahead of corn in a two-year corn-soybean rotation, treatments should be focused on the corn side of the rotation while measuring the follow up effects on soybean to get a full picture of rotational benefits.
Current limestone guidelines are based on the Sikora buffer. Historical lime guidelines were based on the SMP buffer index and when changed it was assumed the Sikora and SMP buffers would return the same results. Changes were made to the current guidelines based on data from neighboring states so local data would be beneficial to re-evaluate the current lime guidelines. Little work on lime application has been conducted in the past 15 years in Minnesota even though questions arise as to the economic benefits, specifically to soybean which is thought to be more sensitive to low soil pH. Minnesota is divided into two zones that differ based on subsoil pH. Area 1 constitutes the eastern part of Minnesota where subsoil pH is generally acid due to carbonate layers that are deeper in the soil profile and Area 2 where subsoil pH is higher due to shallower carbonate layers. Even though subsoil pH values are higher in Area 2 the surface soil pH can be very low. However, past research has not demonstrated large economic benefits to lime for Area 2. The result of this project should provide evidence whether the current lime calibrations are correct and give some direct evidence on the economic benefits to lime application. I am also looking to generate data on the potential to acidify soils with a high soil pH. Some suggest acidifying soils as a method to reduce IDC severity. The buffering capacity of most soils makes acidification generally not feasible and likely cost prohibitive to lower soil pH. Data could be generated in a lab setting to provide Minnesota soybean growers whether soil acidification is practical.

The final goals of this project are to establish some product testing trials, specifically testing in-furrow or near-seed liquid fertilizer application to soybean. While not suggested I do receive questions from soybean growers about liquid fertilizer and whether new placement methods or low-salt sources could be used to increase soybean yield. Growers trying to reduce costs that do not want to broadcast fertilizer and have the option for in-furrow placement would benefit from additional information regarding different placement options. I am specifically interested in testing the Furrow-jet system offered by precision planting which places fertilizer off to the side of the seed which may reduce the potential for seedling damage and reduced emergence. It is much easier for me to test these types of systems instead of a soybean grower who is at greater risk for loss should the fertilizer and placement significantly reduce emergence. There is data the negative impacts of in-furrow fertilizer application to soybean collected in Minnesota about 20 years ago, the Furrow-Jet system was not available at that point in time. The goal of this project would be to evaluate emergence and yield effects on soybean grown in medium to slightly high soil test P and K concentrations.
This pre-proposal submitted to the Minnesota Soybean Research and Promotion council will continue new or on-going research project that were funded for 2023.

1) Evaluate the impact of liming on yield of soybean and crops grown in rotation with soybean over a 5-year period.
a) Evaluate current limestone guidelines to determine if rates are correct to achieve desired pH values.
b) Determine whether the Sikora buffer pH returns values compared to the SMP buffer which was previously suggested for use in Minnesota.
c) Re-establish boundaries for Area 1 and Area 2 soils based on soil series changes based on subsoil pH levels versus the current map based on county boundaries.

2) Determine whether pell-lime can be banded or broadcast at low rates with and without sulfur to enhance soybean yield grown in rotation with corn.
a) Quantify the economics of pell-lime application banded or broadcast prior to corn in a corn-soybean rotation.
b) Determine if the source of sulfur applied in a two-year corn soybean rotation affects soil acidity and if this impact is affected by fertilizer placement.
c) Determine if low rates of pell-lime can be effective an increasing soil pH, mitigating the acidity produced by sulfur fertilizers, and can increase soybean yield.

3) Quantify the impacts of sulfur source and placement prior to corn on the proceeding soybean crop.
a) Evaluate the impact that sulfur band applied and broadcast to corn may have on corn and soybean yield over time in a 2-year corn-soybean rotation.
b) Assess the impact of sulfur application on corn and soybean plant tissue concentration
c) Compare source and placement of sulfurs impact on post-harvest soil test sulfur concentrations

4) Determine whether in-furrow N-P-K starter can increase soybean yield in medium-high testing soils.
a) Compare the effects of two liquid fertilizer sources applied in-furrow on soybean grain yield that vary in salt index values.
b) Evaluate the impact of in-furrow starter on soybean seedling emergence.
c) Refine fertilizer placement guidelines for soybean.

1. Re-evaluation and potential overhaul of current lime guidelines
2. Economic analysis of benefits to limestone application for Minnesota cropping rotations over a period of five growing seasons
3. Economic analysis of sulfur application in a two-year corn soybean rotation based on source of sulfur and placement
4. Economic analysis of application of pell-lime for soybean grown on soils with pH less than 6.0. The analysis will compare broadcast and band application methods and determine how much soil pH can be increased using continual low rates of pell-lime
5. Assessment of the impact that sulfur fertilizer source has on decreasing soil pH over time in a two-year corn-soybean rotation.
6. Assessment of the viability of acidifying high pH high lime content soils.
7. Updated soybean fertilizer guidelines for the following aspects:
a. -Guidance on best practices for lime application
b. -Additional information to update current sulfur guidelines or soybean
c. -Soybean seed tolerance to fertilizer placement on and near the seed at planting
8. One crop e-news blogs
a. Update on changes to soybean fertilizer guidelines with a focus on chloride research results

Updated August 30, 2024:
Work is progressing on all objectives for the current project. The following is a brief update of work for each of the four research objectives.

1) Evaluate the impact of liming on yield of soybean and crops grown in rotation with soybean over a 5-year period.

A total of 7 field trials are currently in place across Minnesota. New field trials were added in 2024 located in Farmer fields near Le Center, Gibbon, and Sandborn. Sites were carried over that are located at research and outreach centers at Becker, Lamberton, Rosemount, and Waseca. All studies but 2 are in corn in 2024. The two non-corn studies are planted to soybean. All work has been completed as planned by the end of this quarter.

2) Determine whether pell-lime can be banded or broadcast at low rates with and without sulfur to enhance soybean yield grown in rotation with corn.
3) Quantify the impacts of sulfur source and placement prior to corn on the proceeding soybean crop.

Corn was planted and fertilizer re-applied at Rosemount and Waseca to the same plots fertilizer was applied in 2022. Soybean was planted at Lamberton and Rochester but no treatments were applied as outlined in the methods. All plant samples and measurements have been collected as planned at all locations. Sites have been prepared and are ready for harvest when the crop is mature. I have nothing to report as none of the sites has been affected by adverse weather at this time.

4) Determine whether in-furrow N-P-K starter can increase soybean yield in medium-high testing soils.
Field trials were established as planned at Rosemount and Lamberton. Treatments compared were 10-34-0 and 6-24-6 at both locations. All treatments were applied as planned. Stand counts were collected as planned from both sites. No plant tissue samples were to be taken at either site. The only remaining work to complete at either site is harvest.

Updated December 3, 2024:
Work is progressing on all objectives for the current project. The following is a brief update of work for each of the four research objectives.

1) Evaluate the impact of liming on yield of soybean and crops grown in rotation with soybean over a 5-year period.

Yield data was collected from all 7 of the current locations. Data has been compiled but I have not had time to go through and fully analyze the data for a formal report. I am looking for 3 additional sites to start for 2025 but none of the sites will likely be established in fall of 2024.

2) Determine whether pell-lime can be banded or broadcast at low rates with and without sulfur to enhance soybean yield grown in rotation with corn.

All yield, plant, and soil samples were collected from the four locations as planned. Yield data has been collected and compiled but has yet to be summarized formally.

3) Quantify the impacts of sulfur source and placement prior to corn on the proceeding soybean crop.

Corn was planted and fertilizer re-applied at Rosemount and Waseca and yield data was obtained for 2024. Soybean yield data were collected at Lamberton and Rochester as planned. Work is progressing as planned to complete all project objectives as is outlined in the proposal.

4) Determine whether in-furrow N-P-K starter can increase soybean yield in medium-high testing soils.

Field trials were established as planned at Rosemount and Lamberton. Treatments compared were 10-34-0 and 6-24-6 at both locations. All treatments were applied as planned. Stand counts were collected as planned from both sites.. Harvest was completed and a preliminary analysis of the data are included in the attached report form.

View uploaded report

Updated February 28, 2025:
Work is progressing on all objectives for the current project. The following is a brief update of work for each of the four research objectives.

1) Evaluate the impact of liming on yield of soybean and crops grown in rotation with soybean over a 5-year period.

Yield data was collected from all 7 of the current locations. I have not found any major impacts on corn or soybean yield from lime even in the locations where lime was applied in 2023. However, soil pH data from fall samples still is not showing major changes in pH at some of the locations. I found larger pH changes in the 2024 sites. All sites should be carried forward to 2025 with the addition of possibly 3 additional locations.

2) Determine whether pell-lime can be banded or broadcast at low rates with and without sulfur to enhance soybean yield grown in rotation with corn.

All yield, plant, and soil samples were collected from the four locations as planned. Yield data has been collected and similar to previous years we have found no impact of the pell lime on corn or soybean yield. However, we have not found much of an increase in soil pH across the study locations at this time so it may be too early to tell whether the pell lime will have a major impact on potential acidification of the sulfur treatments.

3) Quantify the impacts of sulfur source and placement prior to corn on the proceeding soybean crop.

Corn was planted and fertilizer re-applied at Rosemount and Waseca and yield data was obtained for 2024. Soybean yield data were collected at Lamberton and Rochester as planned. Work is progressing as planned to complete all project objectives as is outlined in the proposal. Data has been compiled and I analyzed the sulfur data to be used for a poster for Ag Expo in January. There was a response to sulfur t both corn locations but none of the soybean locations. I currently am waiting for some of the final results for the tissue analysis but I have all of the soil analysis from the 2024 studies.

4) Determine whether in-furrow N-P-K starter can increase soybean yield in medium-high testing soils.

Field trials were established as planned at Rosemount and Lamberton. Treatments compared were 10-34-0 and 6-24-6 at both locations. All treatments were applied as planned. Stand counts were collected as planned from both sites.. I included information for the study in a poster which was presented at Ag Expo. There was a negative impact of starter on soybean emergence but yield was not greatly impacted. The lack of a yield response shows that there is no positive benefit to starter on soybean within these trials. However, none of the trials were low in P or K so the expected benefit from starter if there is not a nutrient deficiency would be low.

Updated May 30, 2025:

View uploaded report

This proposal contains three separate projects that are all part of on-going multi-year research studies.

Study 1 focuses on rates and sources of limestone and the impacts of liming on corn and soybean grain yield and profitability over a five-year span after initial application. Three studies summarized for this report are in year 2 or 5 and four studies are in years 1 of 5. There has been no impact of lime application rate on corn or soybean grain yield to date at any location. There have been isolated impacts of lime source on crop yield which do not make sense if there is no impact on rate. It would be expected to see significant changes in pH that would impact crop yield starting 2 years after application but at this time the 2-year data do not show a benefit. However, all the 2-year sites were planted to corn which will be rotated to soybean in 2025. Economic impacts of lime were calculated but will not be reported in this summary as the would be a negative impact overall of lime on profitability since grain yields were not impacted. The lack of an impact on grain yield in the short-term is why longer-term studies over multiple years are needed for lime research.

Soybean seed protein concentration was impacted by lime application for some of the first-year trials. Seed protein concentration was greater in some instances indicating that there may have been some impact of the lime on accumulation of nitrogen and possibly nodulation. Yield however was not impacted by lime so profitability would not have been increased unless the small change in protein concentration would have an impact on the value of the crop.

Study 2 was established to determine whether there is a difference in the response to sulfur based on source and placement of sulfur ahead of the corn crop in a 2-year corn soybean rotation. Pelletized lime was added with the sulfur to determine whether a low rate of Pell lime could benefit corn or soybean yield. Soybean planted in year 2 did not receive additional fertilizer such that the impacts of the previous year’s sulfur application on soybean could be studied. To date we have completed 1 full 2-year rotation at four locations and in 2024 the second corn-soybean rotation, and second sulfur and lime application, was made at two of the four locations.

In years 1 and 2 we saw very sporadic impacts of sulfur mostly on tissue sulfur concentration and in some cases increased sulfur concentration and sulfur containing amino acids in the soybean grain when sulfur was applied. Corn grain yield was seldom impacted by sulfur applications in the first year at each location and the following soybean crop grain yield was not impacted by sulfur source or placement and the addition of pell-lime at any location. However, corn grain yielded greater with sulfur applications at 2 locations in 2024 (year 3 at each location) following the second application of sulfur and the increase in yield occurred regardless of the source of sulfur applied (AMS, K-sulfate, and K-MST). A lack of yield response in year 1 would follow some of my past studies. Concurrent funded research has been showing that sulfur application even in the sulfate form may carry over for 1 or 2 years post application and the lack of an impact of the sulfur treatments in year 1 at the four locations studied may simply be a result of sulfur that remained in the soil following applications made to the field areas one or two years before the trials were established. I am expecting to have a higher probability of differences in yield in the soybean year 4 (2025) at the two locations where corn yield was greater in 2024. There is likely an impact of sulfur on soybean yield in Minnesota, but the research generally shows that application ahead of the preceding crop typically will supply enough sulfur where a direct application in not warranted to soybean.

Study 3 focused on starter fertilizer use for soybeans. Starter fertilizers placed on the seed can be damaging to soybeans and in-furrow starter fertilizer is not suggested for use for soybean in MN. However, we wanted to determine whether there is a difference between placement directly on the seed with a dual side-band placement with the precision planting furrow jet system. To date research has been completed at four locations comparing 10-34-0 with a lower salt fertilizer such as 6-24-6 or 3-18-18. The data has clearly shown a significant impact of the in-furrow starter application on reducing soybean seedling emergence regardless of the source of fertilizer used. The dual side band application has shown some potential for reducing negative impact on emergence about 50% of the time. Soybean seed yield did not show any major reductions regardless of reduction in stand from the starter application. Seed yield was never increased and even with a lack of a reduction in yield the significant loss in stand is troublesome and I would not suggest that growers place any N-P-K fertilizer in a band close to the soybean seed. Since yield was not increased there was no circumstance where the additional cost of the fertilizer was paid for and the use of starter would present undue risk for a soybean producer in Minnesota except for growers using in-furrow iron chelates to correct issues related to iron deficiency chlorosis where these chelates have not been shown to decrease emergence and have demonstrated a potential for increasing yield in IDC prone soils.

We know a lot about the benefits of major macronutrient applications to soybean based on past research. However, there are a few areas that I continually get questions on as to how to boost soybean yield. The first is sulfur applications. Almost all my current soybean research on sulfur is in one-year studies where sulfur is directly applied to soybean. However, past results have indicated more consistent results in conventional tillage where sulfur was applied ahead of the preceding corn crop benefiting the corn and the following soybean crop. Long-term research trials need to be established looking at sulfur over the rotation. This data will benefit soybean growers by giving a refined set of sulfur fertilizer guidelines for soybean which are based on economics of application. In addition, we know that fertilizer application can impact pH through soil acidification, and that soil pH impacts soybean nodulation. I do not know of any current or past research where the acidification of the soil following sulfur application has been assessed. Sulfur forms do vary in how they can acidify the soil and comparisons need to be made to provide soybean growers with information on the overall risk for soil acidification and potential negative impacts on soybean.
Limestone can be an expensive input and one thought would be that the application of small rates of pell-lime could be more cost effective in the short term than a larger rate of ag lime particularly for soils in central and western Minnesota where there has not been widespread evidence of positive economic benefits to lime. A long-term assessment of low rates of lime applied in a two-year corn-soybean rotation can allow for an option for soybean growers wishing to boost yield while minimizing cost. In addition, more information on long term yield benefits would be beneficial to determine when and where limestone would enhance soybean production and yield other rotational crops. Establishing actual data on yield benefits from liming is needed for soybean growers when determining whether to apply lime on their own ground as well as when discussing the need for lime with their landowners on rented ground.
The final part of this study will assess the impact of new placement methods of liquid fertilizer on soybean seed emergence which is needed to determine whether these new methods of application are truly “seed safe” to soybean.