Potassium Available to Corn Plants Extracted by Ammonium Acetate, Ammonium Chloride, Mehlich-1 and Mehlich-3 Solutions in Southern Brazilian Soils

ABSTRACT

The main Brazilian soil testing laboratories use Mehlich-1 solution for the determination of available potassium in the soil. However, this procedure has chemical and operational limitations. In search of alternatives for Mehlich-1, this study was to compare different extraction solutions, vis: Mehlich-1 and 3, and 1.0 mol L⁻¹ ammonium chloride (NH₄Cl) and 1.0 mol L⁻¹ ammonium acetate (NH₄OAc), as soil-K index to predict K availability to corn plants in southern Brazilian soils. The greenhouse pot experiment consisted of 30 soils grown with 2 corn crops. All soil-K index presented high correlation and determination coefficients between K uptake by corn plants and the K extracted from the soil. The Mehlich-1 solution was consistently better correlated with K uptake by corn plants than NH₄OAc and NH₄Cl but extracted less exchangeable K of the soils. Grouping soils with similar mineralogy and physicochemical properties enhances and improves the prediction of K availability for corn plants. Moreover, the K saturation index can be used as a sole indicator of K availability to plants. Overall, the results indicate that it is feasible to replace the traditional solution Mehlich-1 in the extraction of soil exchangeable K by solution of NH₄Cl mol L⁻¹ in laboratories that have an Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES).

KEYWORDS:

• Multielement extractor
• potassium saturation index
• multiple soil classes

Additional information

Funding

This project has been funded, in part, by the Soil Testing Laboratory (LAS) of the Soil Department of UFRGS and by FAURGS (Foundation of Federal University of Rio Grande do Sul).