Soil and highbush blueberry responses to fertilization with urea phosphate

The low availability of soils with an appropriate pH value (4.2-5.2) is a factor limiting an increase in highbush blueberry acreage. The experiments examined the influence of a physiologically acidic urea phosphate fertilizer on the pH change of the soil and the mineral content in the soil, leaves, and fruit as well as polyphenols in the fruit of two highbush blueberry cultivars – ‘Sunrise’ and ‘Brigitta Blue’. The fertilizer, at doses of 30 and 60 kg of nitrogen per hectare, was used in the experiments in each of the three years of the study.

After using 60 kg N ha⁻¹, urea phosphate caused a reduction in soil pH. It also significantly influenced the total soil nitrogen content – the average for the cultivars was 7.40 mg in 2015, while in the control plots – 1.85 mg 100 g⁻¹. These quantities are above the optimum recommended for highbush blueberry. At the same time, low amounts of this ingredient were found in the leaves (‘Sunrise’ – 1.83 mg; ‘Brigitta Blue’ – 1.77 mg 100 g⁻¹).

Even after the application of 30 kg of fertilizer in the second year, the phosphorus content in the soil was at a high level (> 4 mg 100 g⁻¹). The amount of phosphorus also increased in the leaves and fruit. Despite considerable quantities of available magnesium in the soil after urea phosphate application, a significant reduction of this component was observed in the leaves and fruit compared to the unfertilized control bushes. The applied fertilizer reduced the amount of polyphenols in the fruit of the tested cultivars.