Project Details:

Title:
Assessment of Soil Potassium Bioavailability and Improving Diagnostics Tools for K Management on Soybean in Kansas

Parent Project: This is the first year of this project.
Checkoff Organization:Kansas Soybean Commission
Categories:Soil fertility, Soil and tillage management, Water quality & management
Organization Project Code:1951
Project Year:2019
Lead Principal Investigator:Dorivar Ruiz-Diaz (Kansas State University)
Co-Principal Investigators:
Keywords:

Contributing Organizations

Funding Institutions

Information and Results

Click a section heading to display its contents.

Project Summary

The project will be conducted on university experiment fields and on-farm sites with cooperating farmers in eastern Kansas. Selected locations will be included in central Kansas to evaluate soils with different mineralogy and soil potassium (K) levels. We will work with Regional Extension Agronomists, County Agents and Commission Members to identify potential cooperators. Identified fields will be soil sampled to determine K levels.

Soil samples at the 0-6 inch depth will be collected from the study area, split in two samples and processed as: 1) traditional air-dry and ground samples, and 2) moist samples for lab analysis. Soil test extraction methods will be used for both dried and field-moist samples including ammonium acetate and Mehlich-3 K. In addition, detailed clay characterization (and overall soil texture) will be completed for each location to determine the possible effect of clay types in Kansas that might affect critical values for K and bioavailability during the growing season.

Correlation and calibration will be completed based on yield response for all test methods. Fertilizer application treatments will include a control plot (0 K) and 50, 100 and 150 lbs of K2O as KCl (potash) applied as broadcast prior to planting; in addition to one in-season K fertilizer application for a total of five treatments. Total plant nutrient uptake will be evaluated during the growing season by tissue analysis for total K. Soybean whole plant samples will be collected at the V3 stage, whole plant K uptake at the R1 stage, and whole plant biomass and the uppermost trifoliate at the R2-R3 stage and analyzed for total K. These measurements will be used to estimate K uptake and K use efficiency with fertilizer application and correlated to the soil tests evaluated in this study. At harvest, yield will be recorded for each plot and a seed sample will be collected and analyzed for K removal, and stover samples collected for estimation of K recycling from soybean after harvest.

Project Objectives

The overall objective of this project is to improve potassium (K) 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:

1. Determine the impact of K deficiencies on soybean yields for different soil types in Kansas.

2. Evaluate current soil test interpretations for K fertilization in soybean, including the evaluation of new soil test methods and the effect of soil clay types on critical levels for soybean.

3. Assess plant K levels during the growing season and determine possible yield limitations related to the high rate of K uptake in high yielding systems.

Project Deliverables

The observed soybean K deficiency problems in parts of Kansas is likely impacting yield, and can be corrected through fertilizer applications based on accurate soil test critical values and/or plant tissue data and adequate for soil types. Preliminary work funded by the Soybean Commission more than 10 years ago showed impact on soybean yield and the need for a revised/updated this nutrient diagnostic tool.

Results will be delivered to Kansas producers and crop advisers in various ways. Information will be disseminated through field days, KSU Soybean Production Schools, extension publications, and the KSU nutrient management webpage. Results of field experiments and any revised recommendations that arise will be summarized and distributed to the public via news releases. Brief articles will be prepared for publication periodically in the Kansas State University Agronomy eUpdates. Results will be shared with county/district extension agents in the state who provide information to soybean growers on a regular basis. Finally, this work will be completed in close collaboration with the KSU soil testing laboratory, and results will be shared with the KSU soil testing lab as well as private laboratories who advise Kansas growers each year.

Progress of Work

Updated July 9, 2019:
A total of five locations were established for the 2019 season, with emphasis on K deficient soils but also including one location with K levels considered optimum. Soil samples were collected and currently under analysis with the different proposed methods.

Updated September 16, 2020:
Studies were established at 5 locations during 2019 with focus on K deficient soils, but also including a location with traditionally high K level. Soybean growth was generally at optimum condition for most locations with potential for good yields, and visual response to K fertilization, as well as P for locations with low soil test P. Soil samples were collected from each individual plots before treatment application and sent for analysis including chemical, physical and biological tests. Soybean plant tissue was also collected at all locations and preliminary results are currently under statistical analysis.

Methods for soil test K are currently under analysis, including traditional K test, analysis on moist samples, and in-season ion-exchange resin as indicator K supply during the growing season. Clay analysis is also ongoing for current field study locations, and additional samples will be collected across soybean producing regions to evaluate the predominant clay species and correlation to K supply.

Updated September 16, 2020:
Studies were established at 5 locations during 2019 with focus on K deficient soils, but also including a location with traditionally high K level. Soybean growth was generally at optimum condition for most locations with potential for good yields, and visual response to K fertilization, as well as P for locations with low soil test P. Soil samples were collected from each individual plots before treatment application, and sent for analysis including chemical, physical and biological tests. Soybean plant tissue was also collected at all locations and preliminary results are currently under statistical analysis.

Methods for soil test K are currently under analysis, including traditional K test, analysis on moist samples, and in-season ion-exchange resin as indicator K supply during the growing season. Clay analysis is also ongoing for current field study locations, and additional samples will be collected across soybean producing regions to evaluate the predominant clay species and correlation to K supply.

View uploaded report Word file

Final Project Results

Updated September 16, 2020:
The 2019 field locations were harvested to measure yield response, plant samples were collected, and fall-spring soil sampling completed. Field experiments were also conducted at two locations during 2019 to evaluate the alternative soil test methods (ion exchange resin, CER). Treatments included a control (check) with no K application and one with an application of 150 lbs K2O acre-1 (high K rate).

Preliminary results showed that plant K uptake measured at reproductive stages (R2, R4, and R6) was increased by K fertilization. However, differences were not statistically significant (p < 0.05) at locations with high soil test K. In contrast, locations with low soil test K showed significantly higher plant K uptake measured at R2 (p < 0.05), R4 (p < 0.10), and R6 (p < 0.05) stages when 150 lbs K2O acre-1 was applied.

At the R6 stage, fertilized plots had 50% more K uptake and 40% more K adsorption (cumulative) by CER compared to the control. This observation suggests the potential use of CER as an indicator of K supply to soybean in field conditions, but further research is needed and ongoing in 2020. In both locations, CER was able to adsorb more K (measured as cumulative adsorption) at a high K rate. The amount of K that was adsorbed by the CER was influenced by soil moisture content. Field evaluation of crop response and soil test methods will continue during the 2020 soybean growing season.

View uploaded report PDF file

Benefit to Soybean Farmers

Improved 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.

Performance Metrics

Project Years