Optimizing fertilizer inputs for soybean production is important to ensure costs are reduced and maximum yield can be achieved. Potassium is a key component to achieve maximum soybean yield, but current research has demonstrated that chloride in potash can reduce soybean yield under certain circumstances. Yield reductions have range from 1 bushel per acre to close to 20 bushels per acre when high rates of chloride are applied ahead of soybean. Soybean growers need a better understanding of when issues related to chloride are more prevalent to ensure they are not purchasing inputs that will reduce yield. Current research has demonstrated that potash can reduce soybean yield and that most, if not all, varieties grown in northern growing regions are chloride includers and more susceptible to chloride toxicity. Some research has indicated that changing timing of when potash is applied for soybean, for example applying high rates ahead of rotational crops, can reduce the risk for yield loss. Other possible methods to reduce the risk for yield loss need to be assessed as there are soils where higher rates of potassium are needed to ensure maximum soybean yield can be achieved. One such report from the eastern Corn-Belt has indicated the application of sulfur can possibly enhance yield when potash is applied. This data needs to be followed up on with a research study including different rates and sources of sulfur to determine whether the greater yield is due to sulfur. Three research trials were established in 2021 and I am requesting one additional year to further evaluate the potential for sulfur to reduce the risk for a yield reduction in soybean following the application of potash. One area I am interested in is whether sulfate, which is an anion like chloride, might reduce the uptake of chloride by the soybean plant. Chloride uptake is not regulated by plants and if present chloride will be taken up as water is taken up by the plant. Could sulfate reduce the risk for chloride toxicity in soybean?

There is increasing interest in applying sulfur ahead of crops to increase yield. It is commonly known that the conversion of some nutrients 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 of 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.

1) Determine if the application of Cl has negative effects of soybean grain yield and quality and whether sulfur application can maintain high soybean yield in the presence of Cl.
a. Quantify yield impacts for high rates of Cl applied as KCl or CaCl2 on soybean yield and grain quality.
b. Determine whether the application of sulfur can reduce the uptake of Cl by the soybean plant reducing the risk for yield loss from high levels of available Cl.
c. Develop a set of fertilizer guidelines for soybean to reduce the risk for yield loss due to Cl.

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

1. Establish whether sulfate uptake can interfere with the uptake of Cl by the soybean plant reducing the risk of chloride toxicity
2. Establish whether amino acid distribution is impacted by K, S, or Cl fertilization
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. -Revised guidance on how to mitigate negative impacts on Cl
b. -Guidance on best practices for lime application
c. -Additional information to update current sulfur guidelines or soybean
7. One crop e-news blogs
a. Update on changes to soybean fertilizer guidelines with a focus on chloride research results

Objective 1 Methods (Year 3 of 3): Three field studies will be established at University of Minnesota research centers located at Becker, Lamberton and Morris. A single high-yielding soybean variety will be selected for each location. Three large blocks will be established, replicated four times, where no Cl and either 500 lbs Cl as KCl or CaCl2 will be applied in spring prior to planting. Main blocks will be subdivided into 6 sulfur treatments consisting of two sources, AMS and gypsum, applied at three rates (0, 15, 30 lbs S). Trifoliate samples will be taken at R1 to assess Cl uptake. Trifoliate samples will additionally be analyzed for Total S content by dry combustion. Grain yield, seed weight, and protein, oil, and amino acid distribution will also be measured. All studies will be run 1 year at each location and discontinued after the 2022 growing season.
Objectives 2&3 methods (Year 1 of 7): Field studies will consist of corn soybean rotations established over a period of two years at four locations using a single corn hybrid at each location. All treatments will be applied before the corn crop. The goal for this study will be to set up two-year corn soybean rotations where treatments will be re-applied always ahead of the corn. Soils will be targeted that have a soil pH of less than 6.0 (closer to 5.0 would be ideal). Three sources of sulfur will be applied at 25 lbs of S per acre. Sources will include ammonium sulfate (AMS), potassium sulfate, and potassium MST (Sulvaris/Nurien). Potassium MST is a micronized elemental sulfur fertilizer source that is co-granulated with potash (like microessentials from Mosaic). I am selecting this source as it is nearly all elemental S at the S source in the product compared to micro-essentials which contains a 50/50 mix of AMS and elemental S. Both K MST and K sulfate only contain K and K and will eliminate the use of MAP or DAP which contain S impurities that can make it difficult to determine differences among S sources. Nitrogen and K will be balanced across treatments at the time of application. If P is needed 6-24-6 will be applied two inches to the side of the seed.
Pell lime will be added in combination with the sulfur treatments at a single rate. The target rate for the pell-lime application will be 200 to 250 lbs but may be adjusted up or down based on starting soil pH and cost of the product. All treatments will be applied with a research grade fertilizer spreader either broadcast to the soil surface or banded using a coulter injection system to a depth of 4-6 inches. Lime will always be applied the using the same application method as fertilizer for a given plot. A minimum amount of tillage will be used at each location as to achieve optimum stand establishment while minimizing disturbance to the bands. All sites will be managed using conventional tillage so it is likely that the bands will be disturbed if a disk chisel tillage system is used after corn before soybean is planted. All trials will be planted using RTK guidance so corn and soybean rows can be planted over the top of fertilizer bands. All plots will contain four crop rows and will be 10 feet wide)
Soil samples will be collected from all plots at a depth of 0-6 and 6-12” prior to initial treatment application and will be analyzed for routine soil measurements, P, K, pH and OM, as well as sulfate-S. Additional 0-6” soil samples will be collected after harvest sampling both in- and between the corn rows and will be analyzed for pH and sulfate-S only (0-6 and 6-12” samples will be collected after soybean is grown but will not be collected in fall 2022). The primary goal of the soil analysis is to determine whether changes in pH are occurring due to the fertilizer placement. I am less interested in sulfate-S in this study so deeper (12-24”) soil samples are not planned. Year 1 will be corn and plant tissue samples will be collected by sampling the leaf opposite and below the ear at R1 and will be analyzed for total S concentration by dry combustion. Corn grain yield and seed weights will be assessed at the end of the growing season.
Timeline:
Below lists the approximate timeline and task broken down by quarter and covers work on all trials for the three outlined objectives.
May-July 2022 – Apply fertilizer treatments and plant corn and soybean field plot trials. Collect soybean trifoliate and corn leaf samples.
August-October 2022-corn and soybean trials will be harvested, collect grain samples for NIR and elemental analysis, collect fall soil samples from the lime trials
November-January 2023-complete processing on soil, plant, and grain samples, submit samples for analysis, and continue compiling grain quality data.
February-April 2023-final analysis of data and a year-end report will be generated.

Update:
I do not have any files to attach for the project at this time. For objective 1, three locations were established. The three locations were the ag experiment stations at Becker, Lamberton, and Morris. Soil samples and plant tissue samples were collected as planned but have not been analyzed at this point in time so there is no data to report. Two locations were established in May 2022 for the sulfur x lime x placement study which encompasses Objectives 2 and 3. Both locations are planted to corn and will be rotated to soybean in 2023. We have collected samples from each of the two locations but have not analyzed any of the samples so no current data are available to report at this time. I should have more data to report for the Next project update. We will start analyzing samples collected in field this fall in my lab and I am hoping we can complete all needed work before the end data of the project which will not necessitate any extensions for the current study. I do not have any outreach to report on this study at this time.

Update:
Fall field work was completed on the two lime and 3 sulfur x chloride trials. Yield data were collected and all planned soil samples were collected post harvest to meet project objectives. Most plant tissue and soil samples are being processed now. I do not have any yield data to report at this time as I still am summarizing and going through the data to clean data for outliers. Plant tissue and soil data collected this fall results should be available starting in January. Right now I am on track for completion of the 2022 growing year project on time. I authored two Minnesota crop news posts using data collected previously by soybean funded projects.

No P, no problem? Skipping phosphorus fertilizer application may make agronomic, economic sense
https://blog-crop-news.extension.umn.edu/2022/10/no-p-no-problem-skipping-phosphorus.html
5 things to know about removal-based P and K strategies
https://blog-crop-news.extension.umn.edu/2022/11/5-things-to-know-about-removal-based-p.html

I have no in-person events to report. In-person events where data will be used from this project will start in December.

Update:
We have completed all field work for the 2022 growing season and the bulk of the lab work is also complete. I am still waiting on analysis of total sulfate in plant tissue that is being conducted by the U of MN soil testing lab for the chloride and the sulfur field trial. I have compiled what data I have currently to look at some preliminary analysis. Data from the chloride trial is similar to past years with larger yield effects due to chloride at the Morris location. The compiled data shows similar yield impacts of chloride sources factoring in the sites across all years and locations. I have only ran a preliminary analysis on the corn data for the sulfur x lime x placement trials. The early season remote sensing work did indicate some differences in greeness at both locations but the yield data showed no impact of sulfur or lime on corn grain yield. The early sensing data did back up visual differences that could be seen early in the growing season. The nature of this work looking at yield across years is more important than one single year and it isn't surprising to not encounter effects on yield in the initial stages of this study.

Blog Posts

Nutrient management on owned vs. rented ground : https://blog-crop-news.extension.umn.edu/2023/01/nutrient-management-on-owned-vs-rented.html. Crop news blog post that utilized some findings from previously funded MN soybean grants looking at P and K timing in corn-soybean rotations.

5 things to know about removal-based P and K strategies : https://blog-crop-news.extension.umn.edu/2022/11/5-things-to-know-about-removal-based-p.html. Similar to above, this blog post utilized ideas which came from projects previously funded by the MN soybean growers but the post was not focused on a specific project.

In person events

I spoke on potassium guidelines at the Nutrient Management conference to around 250 attendees split between in-person and online attendees. The bulk of the talk I had was surrounding a project funded by MN corn but there would have been some data included that came from projects previously funded by MN soybean.

Update:
Final report is being submitted for the project minus soybean grain S concentration data which will be included in the FY23 report as that data is part of an ongoing project.

View uploaded report

Can Cl negatively impact soybean yield? – Yes, the two-year (six site-year) average showed an average yield decrease of 3 bu/ac regardless of the chloride source applied. Past data did show slightly higher yield for potash versus calcium chloride, but this was not supported by the average across locations and none of the locations were deficient in K. The yield reduction from Cl was greater at Morris but effects also were found at Lamberton. The 2022 growing season will be the last year of my current chloride work. I have enough data showing the impacts of chloride on soybean. More work is needed to study the fate of chloride once it is applied to the soil. Seed protein concentration was decreased, and seed oil concentration was increased with potash was applied. Cysteine and methionine were also lower when potash was applied. These effects have been previously found when potassium is applied to soybean (potassium decreases protein concentration).

Does sulfur reduce the impact of Cl on soybean? - There is no evidence that sulfur reduces the negative impact of chloride on soybean yield. The concentration of chloride in the plant tissue was slightly greater when calcium chloride was applied along with gypsum, but this increase in trifoliate Cl concentration did not result in a further decrease in soybean grain yield.

Does sulfur increase soybean yield?- There was no increase in soybean yield with the application of sulfur. Seed protein concentration was slightly higher when gypsum was applied compared to AMS, and oil was lower with gypsum compared to AMS applied as a sulfur source, but there was no effect on the rate of sulfur applied on seed protein concentration. Cysteine and methionine were also slightly higher when gypsum was applied, and both were not affected by sulfur rate.

Did pelletized lime impact soybean yield? – The sulfur by lime study was established with corn planted in 2022. There was no effect of sulfur and lime at the locations at Rosemount and Waseca. Fall soil samples also did not show any change in soil pH, positive or negative, when pell lime was applied.

What is the take home messages to growers? – Soybean yield reduction due to chloride is not a new issue and in the past was largely ignored in northern growing regions as chloride tends to leach from our soils. With more emphasis on higher yield and more fertilizer applied directly to soybean there is some concern when an input may reduce instead of increase yield. I am not telling growers to stop applying potash to their fields. However, potash applications need to be managed to avoid reducing yield of soybean. I currently have not found any widespread need for sulfur applied to soybean. Typically, my best results have been application to a corn crop the year before soybean are grown. I am in the initial years of the lime by sulfur work and more years of data are needed to establish the impacts of sulfur and lime long-term when soybean is rotated with corn.

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 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. This research will also complete my assessment on the negative effects of chloride on soybean in Minnesota. I have been able to establish that soybean yield can be reduced from modest amounts of potash applied directly ahead of soybean and that there is no varietal tolerance to high rates of Cl in most varieties grown in Minnesota. I have started to develop a foundation for guidelines in how to deal with high rates of chloride applied to soybean and this proposed research will complete work addressing whether sulfur can interfere with the uptake of chloride which could give Minnesota soybean producers option should they need to apply potash for their soybean crop.