Factors affecting potassium retention in sandy soils

Potassium (K) is a critical macronutrient for maximizing yields in agricultural crops. However, inconsistent responses to K fertilizer or soil test K levels have led researchers to question which soil properties influence K availability and cycling in soils. This study aimed to evaluate how K is retained in sandy soils. The specific objectives of this research were to (1) determine the influence of pH level on cation exchange capacity (CEC) and K sorption in coarse-textured soils and (2) assess the impact of freeze–thaw cycling on K release across a range of agricultural soils. Soil was collected from 10 agricultural sites in Minnesota. Of these, four were used to evaluate K sorption and eight were used to assess K leaching following freeze–thaw weathering. Potassium sorption experiments revealed that sand-textured soils exhibited limited K sorption as solution K increased, but a higher clay percent or CEC allowed for greater K sorption. The addition of calcium (Ca) in the sorption experiments resulted in K release for all sandy-textured soils. In weathering studies, freeze–thaw cycling led to mixed effects on K leaching. Simulated irrigation water containing Ca and magnesium (Mg) significantly increased K leaching in comparison to deionized water. These studies indicate the need for tailored K recommendations in coarse-textured, low-CEC soils considering the limited K sorption capacity and influence of divalent cations.