Dynamic response of growth and organ nutrient allocation in Ochroma lagopus plantations to water-soluble fertilizer frequency in the rainy season

As a fast-growing tropical tree species, Ochroma lagopus exhibits rapid growth and high nutrient demand. This study investigated one-year-old Ochroma lagopus trees under four fertilization frequencies: control (CK), high (F1), medium (F2), and low (F3). The research examined how water-soluble fertilizer frequency during the rainy season affects tree growth, nitrogen (N), phosphorus (P), and potassium (K) uptake, stoichiometric ratios, and nutrient allometric relationships among organs, aiming to identify optimal fertilization strategies. Results showed that F2 treatment (500 g/plant every 30 days) produced the most significant height increase at 60, 90, and 120 days after fertilization, with a maximum increase of 26.53% compared to CK. The stable nutrient supply promoted preferential "height growth." In contrast, F3 treatment (500 g/plant every 45 days) achieved a 36.58% increase in diameter over CK. The lower nitrogen supply likely avoided potential inhibition of cambium cell differentiation and lignification caused by excess nitrogen, thereby enhancing stem diameter growth and improving plant stability under stress. Nutrient contents and stoichiometric ratios in organs showed stage-specific variations: at 60 days, a "source organ competition" pattern dominated, prioritizing leaf allocation for photosynthesis; by 90 days, photosynthetic products were transported from leaves to roots via branches, enhancing organ synergy and shifting to "source-sink-translocation coordination"; by 120 days, nutrients accumulated in "sink" organs. Allometric analysis revealed that high-frequency F1 caused inter-organ imbalance and elemental conflict; medium-frequency F2 maintained synergistic balance; while low-frequency F3 promoted a "root nutrient reserve" stress-response strategy. Therefore, for Ochroma lagopus plantations, medium-frequency fertilization (500 g/plant every 30 days) during the rainy season is recommended.