(Study 1) Long term Potassium Source Studies Year 4 of 6 (?) – Long term K studies in place from 2009 2018 periodically found yield and grain protein concentration decreases during the soybean year from increasing rates of applied K at poorly drained locations. It is possible that a reduction in yield may be due to the application of Cl in KCl fertilizer. Data from the southern U.S. has demonstrated that soybean grain yield can be reduced due to a high concentration of Cl. It would be beneficial for Minnesota soybean producers to provide a direct link between Cl and the reductions in soybean yield. If we can identify potential when and why yield reductions occur the fertilizer guidelines can be modified to outline best management practices to ensure inputs purchased increase soybean productivity. Antagonism between K and Mg or Ca can also be addressed but it is doubtful that either Mg or Ca would explain the results. The proposed study will help to explain whether the effects on protein and oil are a result of K or Cl.
Methods: Long term trials were established at four locations in Spring 2017 (Crookston, Lamberton, Morris, and Waseca). Two year cropping rotations were established at each site in two blocks, one for each crop. A two-year corn-soybean rotation was established at Lamberton, and Waseca. A two year hard red spring wheat-soybean rotation was established at Morris and Crookston. Treatments are a combination of fertilizer rate, timing, and source. Fertilizer is based on a K application at a K rate of 100 and 200 lbs K2O per acre which is roughly 1 and 2 times expected crop removal for the rotations. Two sources of K, KCl and K2SO4, are compared with a non-fertilized control. An additional source treatment includes CaCl2 (calcium chloride) applied at a rate which supplies an identical amount of Cl as applied in the KCl treatments. The CaCl2 treatment is used to determine if any impacts from KCl may be due to the Cl. Soil Ca content at the beginning of the study was measured, but the Ca applied is not anticipated to have a significant impact on yield. Gypsum will be applied to balance S applied with the K2SO4 so all plots will receive a relatively high rate of S and Ca annually. Timing will consist of all fertilizer applied before soybean or before wheat or corn. A split plot design will be used where main plots will consist of a factorial combination of rate and time while the sub-plots will consist of fertilizer source (none, KCl, K2SO4, and CaCl2). The 2020 growing season will represent the second application of treatments and will complete the second cycle of the cropping rotations at harvest in 2020. Following 2020 I will be evaluating whether to split the soybean plots for future trials if I can locate information on salt includer and excluder varieties which should vary in their tolerance to Cl.
The decision to add the variety component will depend on the soil Cl concentrations at each location following the 2020 growing season and whether information are available on salt includes and excluders for varieties grown in Minnesota. I will include 2-3 trial sites comparing three or four varieties which vary in IDC/salt tolerance to determine if salt tolerance can be used to determine varieties for the split plot treatments in 2021. The studies will be established using a strip plot design with the three to four varieties planted in plot length strips with Cl treatments superimposed over the top of the varieties. There will be three Cl treatments, no Cl and 600 lb/ac or more of Cl applied either as KCl or CaCl2. I will be looking at southern research to determine appropriate rates but the rate should be high enough to induce negative Cl impacts on the crop. Measurements will be limited to a pre-plant soil test composite from each site (similar depths outlined below), trifoliate Cl concentration at R1, soybean grain yield, and grain quality measured by NIR.
Soil samples will be collected after harvest from all plots sampling from the 0-6 and 6-24” depths. All samples will be air dried and ground prior to analysis. Exchangeable K will be determined on the 0-6” samples while Cl will be analyzed on all depths. Exchangeable Ca and Mg was determined on samples collected prior to the 2017 growing season and will be measured again for the fall 2020 soil samples to study changes in K base saturation following the various K rates and treatments. Additional soil samples will be collected in June to be used for soil test K correlation research. June samples will only be taken from the no K plots for each main block (32 per site). June samples will be kept in a field moist state, sieved, and then split where a minimum of 100g of soil is air dried to be analyzed for K while the remaining moist soil is analyzed for K concentration without drying.
Plant tissue samples will be collected from all plots and crops. Wheat flag leaf samples will be collected at anthesis by sampling 30 plants. Corn leaves opposite and below the ear will be sampled at the R1 growth stage. Soybean trifoliate samples will be collected at R1 by sampling 25 fully developed trifoliate samples which include leaflets and the petiole. All plant tissue samples will be dried, ground, and analyzed for K, Ca, Mg, Cl, NO3 and NH4 concentration. Additionally, grain samples will be collected for all crops from all plots, ground, and analyzed for the same elements determined in leaf samples. Soybean and wheat grain will be analyzed for protein concentration and oil will be analyzed on soybean only along with amino acid distribution using NIR. Both the plant tissue and grain data will be included in a running set of databases which include plant tissue K concentration and grain yield response. Within these databases I have been evaluating information provided to soybean farmers on using plant tissue nutrient concentrations to assess whether plant tissue can be used to predict soybean response to S and grain data has been summarized to better track K removal in soybean grain to provide soybean farmers a current value to use to determining crop removal in their fields.
Study 2: Amino acid Study - Research into the impacts of soil fertility on protein and oil concentration have been conducted. The impacts on amino acid distribution has not been widely researched. In Minnesota, research on the impact of sulfur on cysteine and methionine content have been studied for soybean and work is currently underway for hard red spring wheat. Some of the research has shown increases in cysteine and methionine in the grain with sulfur but the impacts on other essential and non-essential amino acids has not been fully researched. Since sulfur can change the content of sulfur containing amino acids but may not change the total protein content of the grain, other amino acids have to be decreased. One amino acid that has shown to be decreased with sulfur is asparagine. More work should be conducted to better understand the distribution of amino acids to determine if nutrient guidelines should be modified to ensure concentrations of desirable amino acids are maximized in soybean grain.
Methods: This study will continue work funded for 2018-2019 by the Minnesota Soybean Research and Promotion council. Data will be tabulated from current and past soybean trials where amino acid data was reported during NIR analysis. Data will be focused on P, K, and S studies where NIR analysis was previously run and includes amino acid distribution. The NIR data should allow for determining trends in changes in amino acid concentration. I have started the database but will plan on continuing adding data as we generate more quality data with current trials. The end product of this work will be developing the foundation for a database that can be updated and analyzed annually to study long-term trends in effects on amino acids based on nutrients applied. I am not requesting specific funds for this work in this proposal as the NIR analysis is requested within objective 1 and I have a selected number of other studies currently where I analyze quality which is covered by other funding sources.
Timeline:
Below lists the approximate timeline and task broken down by quarter. The main funding request if for year 4 of a long-term trial. The main idea of the trial was to establish plots to look at long term K management in soybean. The trial is currently in Phase 1 which involves building soil test Cl levels. Phase 2 will focus on potential differences in how soybean varieties may respond to Cl. At the end of year 4 I will evaluate whether soils are built sufficiently high enough in Cl content to proceed to Phase 2 or whether another 2-year rotation would benefit the project to further increase soil Cl content.
May-July 2020 – Plant corn and soybean field plot trials. Collect wheat and corn leaf samples and soybean trifoliate samples, collect 0-6” soil samples for Moist K analysis.
August-October 2020-corn, wheat, and soybean trials will be harvested, collect grain samples for NIR and elemental analysis, fall deep soil samples collected, apply fall fertilizer for year 4.
November-January 2021-complete processing on soil, plant and grain samples, submit samples for analysis, and continue compiling grain quality data.
February-April 2021-final analysis of data and a year-end report will be generated.
Data generated will be utilized in the revision of “Fertilizing Soybean in Minnesota”. The Soybean fertilizer publication is currently being updated and should be revised prior to the end of the 2019-2020 grant. Data also will be used for oral and written web based extension outreach material. I am looking to also revise the current IDC publication and possibly develop a video which can be released on YouTube related to IDC management. I have been looking to target some of our outreach material released through our Outreach Coordinator funded through AFREC towards crop specific issues. In this case we have several studies previously funded by the Minnesota Soybean Growers which would be a good target for news releases crediting the funding provided by the Minnesota Soybean Growers and the Research and Promotion Council. I am looking to complete a phase I summary from the potassium source trial at the end of the 2020 growing season summarizing the yield data and also taking a look at some of the base saturation data which I will be again looking at following soil sample collection at the end of the 2020 growing season.
The PI has over ten years of research and extension experience in Minnesota developing web based, oral, and in-print extension material. Over the past year we have been utilizing an outreach coordinator funded through AFREC to help develop material which has been released through the Extension Crop E-news blog, developing high quality videos, and podcasting about current research topics. By using this coordinator, we have been able to increase release through earned media. Several of our releases have become radio interviews or have been re-released by ag media such as corn and soybean digest. While the project is funded by AFREC several of our projects overlap so data generated through the Minnesota Soybean Research and Promotion council has been, and will be, released with the help of the AFREC coordinator position. Most of the data generated by this project will be incorporated into print material that is housed in the nutrient management section in the University of Minnesota Extension website. We rely on funding for new projects in order to generate research data to keep our information current which helps increase use of our web based material.
The majority of plant and soil tissue samples will be sent out to public or private labs for analysis. My current lab has the capability to extract soil samples by the field moist method, which we have done for the past ten years. I also will be analyzing all plant and grain tissue for nitrate-N and Cl content for the field study portion of this trial.