Full explanation
Practical meaning for Ukrainian farms: summer Steppe daytime RH averages 45–55% — safe for all fertilizers. Autumn (October-November) Forest-Steppe RH rises to 75–85% → ammonium nitrate in open bags or outdoors for 2–3 days becomes a monolith; urea holds up better. Polissia November-December fog — RH 90%+, KCl requires sealed packaging. Solutions: (a) draft-free store, leak-free roof, wooden pallets 10 cm above the floor; (b) big-bag (500 kg, 1000 kg) FFS sealed packaging outperforms 50 kg sacks; (c) for AN — 6–8 week rotation from delivery to application, no more. Procurement window: August-September for spring application, ahead of Polissia fog. Source: fertilizer-kb.ts `storage_crh_percent` field + Institute of Mineral Fuel NAS.