Compost-nitrogen synergies improve nutrition and growth in citrus rootstocks

• Moderate compost combined with nitrogen boosts citrus seedling growth. • Nutrient balance improves across diverse citrus rootstocks with compost-N. • Compost–N synergy enhances uptake of key macro- and micronutrients. • Rootstock responses vary, highlighting genotype-specific nutrient interactions. • Sustainable fertilization strategies can optimize citrus nursery production. Excessive use of mineral nitrogen fertilizers undermines soil health and sustainability in citrus production. Compost offers a promising alternative, but its interaction with nitrogen and rootstock remains unclear. A factorial experiment was established using Thomson Navel orange grafted onto Citrumelo, Citrange, and Sour Orange rootstocks to evaluate the combined effects of sulfur-enriched compost (0–7.5 % w/w) and ammonium sulfate (0–80 mg N kg⁻¹ soil). Moderate compost (2.5–5 %) combined with moderate nitrogen (≈40 mg kg⁻¹) improved growth and balanced leaf nutrition, while excessive nitrogen reduced uptake of key nutrients. Compost enhanced micronutrients (Mn, Cu), and rootstock strongly influenced Fe and Zn. These results highlight that partial substitution of synthetic nitrogen with compost, adjusted to rootstock responses, is a practical and climate-smart strategy for sustainable citrus management.