Database Research Summaries
2018 Evaluation of Soil Health Test to Determine Fertilizer Needs for Soybean in Kansas

calendar_today Year of Research: 2018
update Posted On: 12/04/2019
group Dorivar Ruiz-Diaz (Principal Investigator, Kansas State University)
bookmark Kansas Soybean Commission

Research Focus

The focus of this project is to evaluate the use of soil health test for fertilizer recommendations and evaluate the relationship between the Haney H3A-4 (H3A4) and Mehlich-3 (M3) soil tests for P and K in Kansas soils.


  • Evaluate commercially available soil health tests for fertilizer management in soybean under Kansas soils and production practices; and compare to traditional soil test methods.
  • Determine the effect of long-term management practices (i.e. tillage system, cover crops, rotations) on fertilizer requirements/recommendations for optimum soybean yields.
  • Develop soil test interpretations for recently proposed soil health chemical indicators (Haney H3A and Cornell modified Morgan), and evaluate the effect of physical and biological factors/indicators on nutrient availability and plant uptake.


  1. Mehlich-3 and H3A4 soil test P and K were positively correlated in the combined data. As expected, the pH buffering capacity of the M3 solution was clearly greater than that of H3A4.
  2. The H3A4 solution consists of a dilute mixture of weak organic acids, and solution pH essentially followed the pH of the soil. In general, H3A soil test P and K were considerably lower than M3 soil test P and K. The relationship between M3 and H3A4 soil test P appears to be strongly influenced by soil pH and alkalinity. This is unsurprising given the differences in pH buffering capacity between the two solutions, and the important role pH plays in the solubility equilbria of most soil P minerals.
  3. The relationship between M3 and H3A4 soil test K also varied between sites, but was not explained well by either soil pH or alkalinity. Differences between M3 and H3A4 soil test K are not surprising, given the different chemical nature of the two extracting solutions. Mehlich-3 contains ammonium (NH4+), which has a similar ionic radius and valence to K+ cations, which allows it to displace K+ from the soil’s cation exchange complex.
  4. While Mehlich-3 and H3A4 soil test P and K appear to be positively correlated, their relationship also appears to be variable. This means new calibration data will likely be required if H3A4 would be used for fertilizer recommendations.


  • This study will contribute with new information and help develop guidelines for accurate interpretation of soil health test for fertilizer management in Kansas.
  • Appropriate fertilizer management will contribute with increased productivity, cost savings, and to minimize the environmental impact.

For more information about this research project, please visit the National Soybean Checkoff Research Database.

Funded in part by the soybean checkoff.