Efficiency of available potassium extractants in soils with 2:1 clays in the semi-arid region of Brazil

Abstract

Evaluating the availability of potassium (K) in soils of the semi-arid region of Brazil is complex, as it varies greatly between soils, especially soils with larger amounts of 2:1 minerals. The aim of this study was to evaluate the efficiency of ammonium acetate, ammonium chloride, Mehlich-1 and mixed ion-exchange resin as extractants in quantifying the K content available to maize plants in soils of the semi-arid region of Brazil. The treatments were distributed in randomised blocks, and included six types of soil (a Red Yellow Argisol, a Fluvic Neosol, two Haplic Cambisols, a Rendzic Chernosol and a Haplic Vertisol) and five levels of K, with three replications. Each plot consisted of a plastic pot containing 3.0 dm3 soil, where two maize plants were grown for 35 days. There was a good correlation between the extractants under evaluation and the amount of K accumulated by the plants. The ion-exchange resin presented a lower K extraction capacity in the more-clayey soils with a higher CEC and greater quantity of 2:1 minerals, and is not recommended for soils with these characteristics. The extraction capacity of Mehlich-1 may be reduced in alkaline soils with high levels of CaCO3 equivalent, and should not be used in these soils. Ammonium acetate extracted the greatest amounts of K from the soils and showed no limitations in any of the soils under evaluation, making it the most recommended for assessing potassium availability in semi-arid soils.