Full explanation
Procedure: (1) SAMPLING — 15–25 points per field at 0–30, 30–60, 60–90 cm depths, mixing same-depth subsamples; (2) PACKAGING — cooled (+4°C), delivered to the lab within 24 h; (3) ANALYSIS — 2M KCl extraction, colorimetric NH₄⁺ and NO₃⁻ determination. Certified Ukrainian labs: NAAS Institute of Soil Science (Kharkiv), Agro-El (Kyiv), ELSA (ISO 17025), Agro-Trade Lab. Price UAH 450–900/sample, 2–5 days. Top-dressing formula: N = Yield_target × 28 − Nmin (kg/ha) − N mineralized from humus (30–80 kg/ha) + starter N. Example: wheat 6 t/ha, Nmin = 45 kg/ha → needed = 6 × 28 − 45 − 60 = 63 kg N/ha top-dress = 190 kg ammonium nitrate. Without the test, farmers typically apply 100–140 kg N/ha «just in case» — a 30–80 kg/ha surplus (UAH 200–500/ha wasted plus environmental risk).