Extractable Potassium as Affected by Soil Moisture Conditions

Abstract

ABSTRACT Soil potassium (K) analysis is a widely adopted tool to evaluate exchangeable K content, but variations in soil moisture before sampling, the drying method, and the extractant used could influence the results. Therefore, the objectives of this work were as follows: evaluate the effect of soil drying before testing on extractable K; evaluate the effect of a short-term flooding on soil K availability; and determine the relationships between field-moist and oven dried soil K concentrations extracted with Mehlich-3 and Ammonium Acetate (NH4OAc) methods, with and without recent K application. Five Uruguayan agricultural soils were incubated in pots at different humidity levels, and they were analyzed field moist (FM), air-dried (AD) and oven-dried (OD), using two different extractants: NH4OAc and Mehlich-3. The K concentration from FM sample were higher than from OD for both extractants, except for the soil with the lowest K value and the non-illitic clay mineral, where the results were opposed. The K concentrations from FM of samples with 100% humidity were higher than those of 50%. No significant effect on K availability was detected due to the occurrence of short-term flooding before sampling. NH4OAc extracted more K than Mehlich-3 in all soils and treatments.