2021
Assessment of Potassium Bioavailability and Improving Guidelines for K Management on Soybean in Kansas
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Contributor/Checkoff:
Kansas Soybean Commission
Category:
Sustainable Production
Keywords:
GeneticsGenomicsSeed quality
Parent Project:
Assessment of Soil Potassium Bioavailability and Improving Diagnostics Tools for K Management on Soybean in Kansas
Lead Principal Investigator:
Dorivar Ruiz-Diaz, Kansas State University
Co-Principal Investigators:
Project Code:
2151
Contributing Organization (Checkoff):
Kansas Soybean Commission
$38,039
Leveraged Funding (Non-Checkoff):
Kansas Fertilizer Funds, $20,000
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Institution Funded:
Kansas State University
$38,039
Brief Project Summary:

The goal of this project is to improve potassium management for soybean production in Kansas, increasing yields with improved diagnostic tools and fertilization strategies based on soil types in the main soybean producing regions in Kansas. Specific objectives include: determining the impact of K deficiencies on soybean yields for different soil types; evaluating current soil test interpretations for K fertilization in soybean, including new soil test methods and the effect of soil clay types on critical levels; assessing plant K levels during the growing season and determining yield limitations related to the high rate of K uptake.

Key Benefactors:
farmers, agronomists, applicators, ag retailers

Information And Results
Project Deliverables

Final Project Results

Update:

View uploaded report PDF file

View uploaded report 2 PDF file

Three experiments were conducted as part of this project to evaluate soil test methods and tissue analysis as diagnostic tools for potassium (K) in soybean. The first study assessed the relationship between K adsorption by cation exchange resins (CER) and K uptake by soybean in field conditions. The study was conducted at two locations with contrasting soil test K levels and two treatments, including a control (0 lbs K2O/ acre) and a high K rate with 150 lbs K2O/ acre applied pre-plant and incorporated. Cation exchange resins were buried in the field in multiple periods to cover the entire soybean reproductive growth stages. In addition, whole plant samples were collected at R2, R4, and R6 stages to measure plant K uptake. Soil volumetric water content and soil temperature were measured using a TEROS 11 sensor. This study found that CER tends to decrease in inverse proportion to plant K uptake, suggesting a measure of soil K surpluses because of root competition. The fertilized plots were able to maintain higher K supply rates during the peak plant demand. Depending on each location, soil temperature and soil moisture content were highly correlated with CER adsorption in control plots.

The second experiment evaluated tissue nutrient concentration and nutrient ratios as predictors of soybean response to K fertilization. It was conducted at 10 locations throughout eastern Kansas during 2019, 2020 and 2021. Four treatments were selected to evaluate soybean response to K fertilization. Treatments included a control with no K fertilization and rates with 50 lbs K2O/ acre increments until reaching a maximum of 150 lbs K2O/ acre. Aboveground plant samples were collected at V4, R2, R4, and R6 stages to measure plant K and Magnesium (Mg) concentration. K concentration and K/Mg ratio at V4 growth stage were well correlated to K uptake at R6 and grain yield. Considering grain yield, the critical concentration range for K and K/Mg ratio was 1.6 to 1.8 % and 2.3 to 2.4, respectively. The nutrient ratio was slightly better in predicting K uptake.

The third experiment compared different soil test K (STK) methods and evaluated the correlation to soybean yield and K uptake response in low testing soils. Additionally, the study assessed the effect of sampling moment on STK results for NH4OAc and Mehlich-3 tests using dry and field moist samples. It was conducted at 10 locations throughout eastern Kansas during 2019, 2020 and 2021. The treatments were a control with no K fertilization and rates with 50 lbs K2O/ acre increments until reaching a maximum of 150 lbs K2O/ acre. Aboveground plant samples were collected at R6 stage to measure plant K uptake. In general, moist tests were better correlated to K response than dry tests, especially with NH4OAc. Among all evaluated methods, the CaCl2 dry and moist, NH4OAc moist, Resin K, and NaBPh4 tests were the best when correlating to relative yield and K uptake. CaCl2 dry is one the easiest and cheapest tests, also having a consistent correlation coefficient (around 0.70 for both variables). Furthermore, it might be an alternative to the NH4OAc moist test because of the high correlation (r=0.91). Three out of ten locations had STK changes for dry samples regardless of K fertilization between fall and the subsequent spring sampling. However, almost all locations had little or no STK change when considering moist samples. Overall, the NH4OAc moist test was one of the best methods to estimate K availability in low testing soils; however, other non-conventional tests like CaCl2 dry might perform similarly but without the typic disadvantages of moist samples.

The United Soybean Research Retention policy will display final reports with the project once completed but working files will be purged after three years. And financial information after seven years. All pertinent information is in the final report or if you want more information, please contact the project lead at your state soybean organization or principal investigator listed on the project.