Distribution of potassium, calcium, and magnesium ions from potassium fertilizers in columns of orchard soils

Abstract

AbstractPotassium (K) in fruit and nut orchards affects productivity, water relations, and crop quality; however, information about K, calcium (Ca), and magnesium (Mg) dynamics in orchard soils is limited. This study evaluates the distribution of K, Ca, and Mg in 30‐cm soil columns following four wetting events over 70 days. Soils were a Hillgate sandy loam, a San Ysidro loam, and a Yolo loam applied with muriate of potash (KCl), microfine sulfate of potash (SOP; [K2SO4]), polyhalite (POLY; [K2SO4·MgSO4·2CaSO4·2H2O]), and an unfertilized control. Soil solution K concentrations measured at 5 cm using a porewater sampler were greater than 1400 mg K L−1 in the Hillgate sandy loam POLY treatment after the first two wetting events. Ca and Mg in soil solution were also greater for POLY when averaged across all four wetting events, likely due to greater Ca and Mg inputs. Extractable K using ammonium acetate, significantly increased after the wetting events resulting in 88% and 75% of the extractable K in the top 0–10 cm of the San Ysidro and Yolo loams, respectively. Leached K accounted for 6.2% of the SOP inputs in the Hillgate sandy, whereas only 0.3% and 1.1% in the San Ysidro and Yolo loams, respectively. Higher K leaching as well as Ca and Mg is likely due to higher cation exchange capacity in loam soils and great porosity in sandy loam soils. Our results show differences in the distribution of K, Ca, and Mg and provide insights into K fertilizer availability for orchard soils.