Potassium Management in Apple Production in North China

Field trials were conducted in Shaanxi, Shandong and Liaoning Provinces to investigate fertilizer use in apple orchards and to study the effect of source, rate and time of potash application on apple yield and quality. The orchard sites in Shandong and Liaoning had low soil organic matter content. The average mineral N, Olsen-P and exchangeable K concentrations in the surface soil (0 to 20 cm depth) were 78, 76 and 238 mg/kg in Shandong and 81, 87 and 103 mg/kg in Liaoning. All these nutrient concentrations decreased with greater depth down the soil profile. Shandong orchard farmers mainly applied chemical fertilizers as the nutrient source (a mean of 667 N/ha, 301 kg P₂O₅/ha and 542 kg K₂O/ha, with no animal manure application. However, apple farmers in Liaoning applied nearly half of the total nutrients using manures. A positive K balance existed in all the soil of all the orchards studied in both provinces.

Apple fruit yield and economic returns significantly increased with K application at all the three locations. Fruit quality was also improved by K application. Application 0.3 kg of K₂O/tree (as KCl) produced similar fruit yield and quality to K₂SO₄, but had better economic benefit. The high application rate of K fertilization reduced the Ca and Mg contents in apple fruit, suggesting that overuse of K could cause issues related to Ca or Mg deficiency. All the treatments with K application showed positive K balances at all the experimental locations. Application of 50% of the recommended K at later crop growth stages such as flowering and fruit expending could be beneficial for fruit yield and quality as well as increase farmer’s income. In summary, the best K management practice was to apply KCl at 0.3 to 0.45 kg K₂O/tree, but apply 50% of the K as basal (at flowering) and the additional half of the K during the fruiting stage.