Autumn fertilisation sets winter wheat up for its most vulnerable months. Phosphorus goes in fully before sowing (it drives rooting), potassium too (frost hardiness and stem strength — Bulgarian long-term trials show around 12 kg/da K2O is needed to keep the soil potassium balance positive), while nitrogen goes in only partially: young plants take up just a few percent of their seasonal nitrogen before tillering, so most of the rate is saved for spring.
The legal frame is strict: no nitrogen fertilisers between 1 November and 5 February on autumn crops, and annual nitrogen caps from 9.0 to 20.4 kg N/da depending on soil and yield. Over-fertilised stands overgrow, freeze and invite disease. Soil analysis turns the generic ranges into a field-specific number — Zemedelko's satellite soil analysis maps nutrient supply by management zone within an hour.