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.

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. 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
7. One crop e-news blogs
a. Update on changes to soybean fertilizer guidelines with a focus on chloride research results

Update:
Field sites were established as planned for 2023. Four locations were established, two in lime area I and two in area II in MN as outlined in the research proposal. All sites are planted to soybean in 2023. Soil samples were taken as planned and all work has been completed on the project planned for 2023. For objectives 2 and 3, soybean were planted at the two locations established in 2022 that were corn in that year. Two additional sites were established in 2023 planted to corn. New sites are at Lamberton and Rochester. All work for the soybean and corn sites were completed except for plant samples not being collected at R2 at Rochester due to hail. All other work in on track to be completed in 2023 in accordance with objectives. Two locations were established at Rosemount for objective 4. One of the locations was mistakenly sprayed assuming the site had Enlist beans which terminated work at one of the two locations. We did get emergence data collected from that site which will complete part of the objectives at the abandoned site. Work at the other site is completed as planned.

Update:
Field work is progressing on all trials. Soybean and corn trials have been harvested and we are in process of collecting all soil samples remaining from the studies to close out the 2024 cropping season. Weather has been a major issue for us. Both the dry weather at some locations and hail did reduce crop yield. While the effect was on the 2023 crops, any sites continuing to 2024 and beyond will not require any changes to application plans and will continue as planned. I will be assessing whether to continue the lime trial established at Becker in spring of 2023 as the soil pH was higher than expected at that location. My current plan is to at least continue the spring 2023 Becker site through 2024 then assess whether it is worth continuing. The soil data will be valuable to use for the lime calibrations even if the yield data did not show any economic benefit. A report for Prarie grains has been generated and will be included as a separate attachment.

View uploaded report

Update:
1) Evaluate the impact of liming on yield of soybean and crops grown in rotation with soybean over a 5-year period.
All field work is complete for the four trials established in spring of 2023. I have all soil and gain quality data from all locations. One key finding from 2023 is that there was no impact of lime on soybean grain yield at any site. However, soybean protein concentration did increase with an increasing rate of lime application at two of the four locations. While the increase in protein was not likely due to lime having a positive impact on grain quality, it likely indicates a potential reduction in protein if soil pH isn’t managed optimally. Two additional sites were established in Fall of 2023 and I will be discontinuing one of the sites, Becker, started in spring of 2023 as the pH was already near optimum and it is unlikely that lime will benefit soybean. I am looking for two additional sites for Spring of 2024 and I will also be incorporating PCC lime into a selected number of locations moving forward.

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.
Work is ongoing. All research was completed as planned in 2023. Results are inconclusive currently as I have not found much of an increase in soil pH from any lime source. The lack of an increase in pH may be due to dry soils and poor reaction of the lime in the soil. This work will continue in 2024.

3) Quantify the impacts of sulfur source and placement prior to corn on the proceeding soybean crop.
Work was completed as planned in 2023. I am still waiting on a portion of the soil and plant analysis to be completed at the date of this report. All samples are processed and submitted to the U of MN soil testing lab. I have no found any impact of sulfur on corn or soybean yield at any location. A second fertilizer application will be made in the spring of 2024 at Rosemount and Waseca. The sites at Rochester and Lamberton will be planted to soybean and will be looking at residual impacts of sulfur on soybean yield.

4) Determine whether in-furrow N-P-K starter can increase soybean yield in medium-high testing soils.
Two sites were established at Rosemount in spring of 2023. There were a few issues regarding the application of the correct fertilizer between the two sites. At one site 10-34-0 and 3-18-18 were applied as planned. The second location compared 3-18-18 and 6-24-6. One of the sites was sprayed with the wrong herbicide which resulted in total loss of the field. We did however collect stand counts before the herbicide application so I am missing yield, but we have stand counts. The stand count data showed a clear impact of the placement of the starter relative to the soybean row and emergence of soybean. 10-34-0 placed directly on the seed significantly reduced seed emergence. The field where 3-18-18 and 6-24-6 did not show significant decreases in seed emergence or yield. However, yield was more variable across sites. The 2023 data demonstrated that the concept of placement in regard to the seed row should be studied further. Two additional research sites are planned for 2024 contingent on funding

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.