Pre-flooding phosphorus-iron interactions and nutrient uptake under flooded rice cultivation in histosols of South Florida

Abstract

Flooded rice (Oryza sativa L.) cultivation on Histosols of South Florida relies on both phosphorus (P) and iron (Fe) which act as co-limiting nutrients, yet P availability is often limited, and Fe frequently deficient reflecting their interaction under redox conditions in saturated soils. Pre-flooding, a period of intentional soil saturation before rice establishment, can be a potential strategy to initiate early redox processes, releasing Fe2+ and mobilizing P bound to Fe oxides. To study this, pot experiments were conducted with three pre-flooding durations (T1, T2 and T3 with 0, 15, and 30 days), measuring both available (Mehlich-3 (M3)) and total P and Fe in soil, along with P and Fe uptake and biomass. The results showed that during the pre-flooding phase, both M3-P and M3-Fe, significantly decreased by 8%, 9.3%, and 6.1% for M3-P, and by 13.5%, 12.5%, and 10.5% for M3-Fe in T1, T2, and T3, respectively. Over the entire experiment, M3-P declined significantly by 14.4%, 18.1%, and 19.4%, and M3-Fe by 11.3%, 12.2%, and 13.6% in T1, T2, and T3, respectively (p < 0.05). In contrast, total P and Fe increased significantly only in T3, both during the pre-flooding phase and across the entire experiment. Regression analysis indicated a stronger relationship between M3-P and M3-Fe with extended pre-flooding (R2: T1 = 0.66, T2 = 0.76, T3 = 0.86), supported by consistently high correlations in T3 (r = 0.78–0.99). Total biomass was highest in T3, statistically similar to T1. Total P uptake was highest in T1, whereas Fe uptake was highest in T3.