Optimizing Potassium Fertilization for Shine Muscat Grapes

The experiment was conducted from July to August 2021, and uniformly growing grapevines were selected for the study. In accordance with the results from our previous study [59 ], 429 kg/ha K₂O of potassium (191 g K₂O per plant) was applied to the field, and this amount corresponded to 2862 kg/ha of complex fertilizer, 918 kg/ha of potassium nitrate, 825 kg/ha of potassium sulfate, and 1242 kg/ha of potassium dihydrogen phosphate. The corresponding amount of fertilizer that a single plant received was as follows: 1272 g of complex fertilizer, 408 g of potassium nitrate, 366 g of potassium sulfate, and 552 g of potassium dihydrogen phosphate. The experiment was set up with five treatments: no potassium fertilizer (control, CK), complex fertilizer (CF), potassium nitrate (PN), potassium sulfate (PS), and potassium dihydrogen phosphate (PDP). Each treatment was replicated three times, with five grapevines included in each replicate and a total of 75 grapevines. Potassium-containing fertilizers were divided equally into three applications according to the total amount and applied to each hole dug 20–30 cm from either side of the tree. The first application of potassium-containing fertilizers was conducted 60 days after flowering and then every seven days thereafter. The potassium-containing fertilizers were applied and followed by irrigation to fully dissolve the fertilizers. The other management practices of the grapevines were the same as in the standard ‘Shine Muscat’ grape production.