Legacy phosphorus lability shifts after Atlantic Forest conversion to sugarcane

Phosphorus (P) fertilisation plays a central role in the high productivity of Brazilian sugarcane systems, yet concerns about inefficient P use and environmental risks from legacy P accumulation remain unresolved. Land use change from native vegetation to sugarcane cultivation in tropical regions can profoundly influence soil P dynamics, with implications for fertiliser efficiency and environmental sustainability. We investigated changes in soil P fractions at three long-term sugarcane fields in São Paulo State, Brazil, following conversion from Atlantic Forest. Using a rapid sequential P fractionation method, we evaluated labile, moderately labile, and non-labile P pools in surface (0-10 cm) and subsurface (10-20 cm) layers. Results showed a significant increase in labile and moderately labile P (Mehlich-3 and NaOH-Pi) under sugarcane, reflecting long-term fertiliser application, while organic P declined substantially, especially in surface soils. Despite two decades of cultivation at some sites, total P did not differ significantly between land uses in the surface layer, indicating limited accumulation of legacy P. Occluded P, representing the non-labile fraction, remained stable across land uses, suggesting limited capacity for further P fixation. Moreover, soils with higher clay content exhibited greater retention of organic P under native vegetation, highlighting the role of texture in modulating P dynamics. These findings challenge common assumptions about legacy P accumulation and suggest that sugarcane systems in Brazil may be more efficient in long-term P use than previously thought.