Combination of right K and P source on apple fruit yield and economic income in Shaanxi

The purpose of this study was to compare the effect of the combinations of potassium (K) and phosphorus (P) fertilizer sources on apple yield and their economic benefit to provide the scientific basis for selecting the right P and K source for apple production. Two P sources, MicroEssentials® (SE, N-P₂O₅-S-Zn 12-40-10-1) and diammonium phosphate (DAP), and three K sources, crystal granular potassium chloride (CGMOP), potassium sulfate (K₂SO₄), and MgK₂(SO₄)₂ were studied.

The experiment was conducted in Fuping County of Shaanxi Province where the average temperature and annual rainfall was 11.4 to 15.2℃ and 460 to 685 mm, respectively. The experiment was located at a 3-year old Fuji apple tree orchard with a density of 2,500 trees/ha. There were five treatments: 1) DAP without K; 2) DAP + K₂SO₄; 3) DAP + CGMOP; 4) SE + CGMOP; and 5) SE + MgK₂(SO₄)₂ + CGMOP. All treatments received urea at 300 kg N/ha, 150 kg P₂O₅ /ha, and 200 kg K₂O/ha, except for the K control treatment. All of the P, 40% of N, and 40% of the K was applied basally during the previous fall after harvest, and the remaining 60% N and K fertilizers were topdressed at the fruit expanding stage.

Compared to the K control treatment, K fertilization increased fruit yield and single fruit weight but the difference between K treatments was not significant. Economic analysis showed that the application of DAP with CGMOP resulted in the highest benefit from K application (US$575/ha), followed by the treatment of SE with CGMOP (US$475/ha), that were US$465 and US$370 more than the benefit from applying DAP with K₂SO₄, respectively. The treatment of SE combined with MgK₂(SO₄)₂ and CGMOP resulted in no benefit due to high fertilizer cost. Thus, the combination of DAP with CGMOP or the combination of SE with CGMOP can be recommended in apple production in Shaanxi.