Assessment of phosphorus and zinc dynamics in a rice growing soil of North-Eastern India under contrasting moisture regimes

Aims: Understanding phosphorus (P) and zinc (Zn) interaction on pant response under contrasting moisture regimes is crucial for optimizing nutrient management in rice growing soils. The current study investigated the effects of graded P and Zn application on their dynamics within soil-plant continuum and finally on predicting grain yield under continuous flooding (W ₁ ) and 50% of maximum water-holding capacity (W ₂ ) using two rice cultivars DRR Dhan 45 (V ₁ ) and IR 64 (V ₂ ). Methods: Pot and field experiments were conducted for two consecutive years (2023-2024 & 2024-2025) followed by batch sorption studies to elucidate the mechanisms governing P and Zn dynamics under different moisture and temperature regimes. Results: P application significantly enhanced soil available P, P uptake, and grain yield, whereas Zn fertilization markedly increased Zn availability and uptake. Although P application reduced Zn availability and uptake, Zn application caused only a marginal decline in P availability in soil without adversely affecting P uptake and yield. The highest grain yield (78 q ha⁻¹) was obtained with the combined application of 60 kg P ha⁻¹ and 25 kg Zn ha⁻¹ under continuous flooding for cultivar IR 64 (P ₂ Zn ₂ W ₁ V ₂ ), demonstrating the complementary effects of adequate P and Zn nutrition. Sorption studies revealed that P adsorption was best described by the Dubinin–Radushkevich model, whereas Zn adsorption followed the Temkin isotherm. Continuous flooding reduced the binding energy, thereby enhancing nutrient availability, while enhanced temperature strengthened adsorption, particularly for P, indicating a better nutrient retention under warmer conditions. Thermodynamic analysis showed that Zn adsorption was spontaneous, whereas P adsorption was non-spontaneous under the experimental conditions. Conclusion: Overall, the study demonstrated that P nutrition was the principal driver of productivity in acidic Terai soils, while adequate Zn nutrition complements P utilization with only negligible antagonistic effects. These findings provide a mechanistic basis for optimizing P–Zn fertilization strategies under changing moisture and temperature regimes to sustain rice productivity.