Nitrogen fertilizer is applied in 2 doses. We spread the first dose in a 0.4 m radius, in the form of a circle around the trunk. We apply 2.5 g of pure nitrogen per tree. In early spring, we use ammonium nitrate, which usually contains 35% nitrogen, or calcium ammonium nitrate (20.5% N), which is better mixed with the soil. We apply the second dose in mid-June. This time, we increase the circle’s radius to 1 m and apply approximately 16 g of pure nitrogen per tree in the form of ammonium nitrate or urea. If the plants are planted densely, we apply the fertilizers in two doses. In the second year after planting, we apply the first dose of nitrogen fertilizer before vegetation begins, but after the soil has thawed, within a 1 m radius; we apply the second dose in mid-June within a 1.5 m radius.
Trees that are already fruiting are fertilized in autumn and spring. In autumn, every 3–4 years, we spread potassium fertilizers. Preferably in the second half of November or at the beginning of December, we spread granular potassium salt (50%) at a rate of 20 g of fertilizer/m2. Fruit plants are sensitive to chloride ions when they are within the root zone during the growing season. During winter, these ions are usually leached beyond the root zone and do not cause harm. If we delay potassium fertilization until midwinter, we must not use potassium salt, but only chloride-free potassium fertilizers (potassium sulfate or, in spring, potassium nitrate). These fertilizers are more expensive but safer. Strawberries, blueberries, black and red currants, and stone fruit trees are the most sensitive to chlorides. In spring, we fertilize trees with nitrogen. For trees older than 4–5 years, we spread nitrogen evenly in early spring at a rate of 6–8 g of pure nitrogen/m2. If we observe symptoms of magnesium deficiency on the leaves of trees, particularly apple trees, and did not use dolomitic lime before planting, magnesium fertilization in early spring is recommended. We spread magnesium sulfate over the bed surface to achieve a dose of approximately 8 g of MgO per 1 m2. This fertilization is usually used for trees beginning to bear fruit. Older trees generally do not suffer from magnesium deficiency because their deeply developed roots find it in the deeper soil layers. The rules given above apply to fruit trees. You can read more about fertilizing fruit trees on the Rynek-Rolny website.