Objectives This study aimed to assess the nutrient demands of major crops in Hainan, clarify the regional differentiation of nutrient inputs, and analyze the mismatch between fertilizer consumption and crop demand, so as to provide a scientific basis for formulating precise and region-specific nutrient management strategies in Hainan.

Methods Based on agricultural production data from Hainan, an accounting framework incorporating crop nutrient demand, organic nutrient return, fertilizer consumption, and nutrient gap was developed. The study systematically evaluated the current status of nutrient supply and demand balance and its spatial differentiation at the county level.

Results The estimated nutrient demands for nitrogen (N), phosphorus (P₂O₅), and potassium (K₂O) in Hainan’s agricultural production were 116.83 × 10³ t, 79.41× 10³ t, and 94.00 × 10³ t, respectively, totaling 290.24 × 10³ t, showing a demand pattern of N > K₂O > P₂O₅. Vegetables/melons and tropical fruits were the primary drivers of nutrient demand, accounting for 29.4% and 28.2% of the total, respectively. The western high-efficiency agricultural zone and the northern metropolitan agricultural zone constituted the dual cores of nutrient demand, collectively accounting for 56.3% of the total. The effective organic nutrient return reached 126.40 × 10³ t, including 36.71 × 10³ t N, 27.11 × 10³ t P₂O₅, and 62.58 × 10³ t K₂O. However, the spatial distribution was uneven, showing a pattern of “higher in the north and east, lower in the south and west”.The northern metropolitan area and the eastern coastal area together contributed 65.8% of the total organic nutrient return. The total chemical fertilizer consumption was 375.96×10³ t, with nitrogen, phosphate, and potash fertilizers application rates reaching 1.9, 1.9, and 3.8 times their theoretical demand, respectively, indicating systemic over application. The nutrient gap showed a significant positive correlation with yields of field crops and vegetables/melons. The eastern coastal agricultural zone and the northern metropolitan agricultural zone were the core areas of chemical fertilizer over application, jointly contributing 64.8% of the total nutrient gap. Qionghai and Wenchang cities together accounted for 36.8% of the over applied chemical fertilizers in the province, serving as the main regional carriers of over application.

Conclusions Agricultural nutrient management in Hainan faces a pronounced contradiction characterized by the coexistence of supply–demand imbalance and strong spatial heterogeneity. On one hand, the dominance of tropical fruit and vegetable production has shaped a nutrient demand pattern of “N>K>P”, which is highly concentrated in the western high-efficiency and northern urban agricultural zones. Meanwhile, fertilizer application exhibits systemic over-application, with potassium fertilizer excess being particularly acute, leading to substantial nutrient surpluses that show significant spatial agglomeration effects; specifically, hotspots of resource misallocation and environmental risk are particularly concentrated in the eastern coastal and northern urban agricultural areas. Therefore, it is essential to develop more precise nutrient management by implementing regionally tailored regulatory strategies, with a particular focus on developing differentiated fertilizer reduction plans for hotspot areas such as Qionghai and Wenchang, so as to promote the sustainable development of tropical agriculture.