Potassium, Calcium, and Magnesium Distribution in an Oxisol under Long‐Term Potassium‐Fertilized Apple Orchard

Most Brazilian soils do not possess sufficient concentrations of available potassium (K) to produce maximum apple yield. Potassium distribution was evaluated with a depth profile of a Humic Xanthic Hapludox receiving K fertilization in an apple orchard, cv. Gala/MM106, at Vacaria, Rio Grande do Sul, Brazil. Treatments consisted of four rates of annual maintenance K fertilization. After 12 years of cultivation, soil was sampled in eight depth increments. Potassium, calcium (Ca), and magnesium (Mg) contents were extracted by Mehlich I, ion‐exchange resin, and ammonium acetate pH 7.0. Long‐term application of K fertilizer resulted in K accumulation mainly in the 0‐ to 30‐cm surface layer, with low K mobilization to deeper layers. Increasing rates of K fertilizer did not affect soil Mg concentration but induced a lower Ca concentration extracted by Mehlich I, especially in the 0‐ to 20‐cm layer. The estimated K2O rate for maximum apple yield was 86.5 kg/ha/year.