Spring barley productivity and environmental performance depend on the synchronisation of nitrogen supply with crop demand, especially under variable hydrothermal conditions. A two-year field experiment was conducted in 2024–2025 on a typical Chernozem in the Right-Bank Forest-Steppe of Ukraine to evaluate fertilisation systems based on compost and vermicompost applied alone or in combination with mineral nitrogen. All fertilised treatments had a planned total nitrogen input equivalent to 50 kg N/ha; however, the organic amendments also supplied additional phosphorus and potassium, so the results are interpreted as fertilisation-system effects rather than isolated nitrogen-source effects. The experiment included an unfertilised control, mineral nitrogen, full-rate compost, compost combined with mineral nitrogen, full-rate vermicompost and vermicompost combined with mineral nitrogen. All fertilised treatments increased grain yield compared with the control, which averaged 5.72 t/ha. The highest two-year mean grain yield was obtained with vermicompost N25 + mineral N25, reaching 7.01 t/ha, followed by full-rate compost with 6.80 t/ha. Compost mainly improved yield through increased spike density, whereas the vermicompost–mineral nitrogen combination promoted biomass accumulation and grain filling. Assessment of CO2-equivalent emissions indicated that fertilised treatments reduced yield-scaled emissions compared with the control. The vermicompost–mineral nitrogen combination showed the lowest emission intensity, at 692.6 kg CO2-eq/t of grain. These results suggest that partial substitution of mineral nitrogen with vermicompost may improve spring barley productivity and estimated carbon efficiency; however, longer-term studies with direct greenhouse gas and soil carbon measurements are needed to confirm the environmental effects.