Effects of different potassium fertilization rates on the vines and the vineyard soil in a long-term field trial

The effects of a mineral fertilization with 150 kg and 300 kg potassium sulphate per hectare and year on the potassium content in the topsoil and subsoil, the potassium content in the leaves and in the must and the generative and vegetative performance of the grape variety 'Grüner Veltliner' were evaluated in a long-term field trial. Soil samplings and soil analyses were carried out in 2009 before fertilization started and in 2016 and 2021. In the topsoil (0 - 25 cm), the potassium contents had increased significantly due to fertilization. In 2021, potassium contents were 19.8 mg, 24.6 mg and 38.1 mg per 100 g of soil, depending on the amount of fertilizer applied. The potassium/magnesium ratio had changed significantly in favour of potassium and the potassium share in the cation exchange capacity had increased significantly. In the subsoil (25 – 50 cm), potassium contents had significantly increased in 2021 only due to fertilization with 300 kg/ha/year. The contents in 2021 were 12 mg, 15 mg and 22 mg per 100 g soil, depending on the amount of fertilizer applied. At the same time, the potassium/magnesium ratio and the potassium share in the cation exchange capacity had also been positively influenced. The potassium content in the vine leaves ranged between 0.91 - 1.50 % depending on the project year and the experimental variant without significant differences between the fertilizer variants in any year. The yield and ripeness parameters, pruning wood weight and the magnesium and nitrogen contents in the must were not statistically significantly influenced by fertilization in any year. In 2020, potassium content in the must was significantly higher in the variant fertilized with 300 kg K₂SO₄ per hectare and year and tended to be higher in the variant fertilized with 150 kg K₂SO₄ per hectare and year than in the non-fertilised variant. In the years 2021 and 2022, both fertilized variants showed tendencies towards higher potassium levels in the must. No significant differences were found between the three fertilization variants in the sensory wine evaluation.