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:
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.