The phosphorus bottleneck in bioenergy-based CDR – and how enhanced rock weathering could break it

Bioenergy plantations are frequently proposed as a cornerstone of carbon dioxide removal (CDR) portfolios, yet their long-term productivity relies on nutrient availability.  Environmental impacts with fertilizer use and finite supply of phosphate rock raise sustainability and geopolitical concerns. Here, we combine global yield observations with a process-based land surface model to assess the role of nutrient limitations in Eucalyptus plantations under repeated harvest cycles and to evaluate whether enhanced rock weathering (ERW) using basalt can alleviate P constraints while delivering additional CDR.

Using idealized global simulations with ORCHIDEE-CNP, we vary nitrogen (N) and P inputs to quantify yield responses and fertilizer requirements. We show that in (sub)tropical regions, high biomass yields cannot be achieved without substantial P additions due to strongly weathered, nutrient-poor soils. In the absence of fertilization, yields decline in most regions over successive rotations as P is progressively exported with harvested biomass. We further compare costs related to conventional and alternative P supply strategies. Increasing carbon prices substantially improve the competitiveness of basalt as a P source, as revenues from associated CO₂ removal from ERW can offset life-cycle costs. At carbon prices above 200 USD tCO₂⁻¹, basalt-derived P could become cost-neutral.  At these prices, basalt provides a cost-efficient and widely available P source with lower eutrophication risks compared to conventional fertilized and potential co-benefits for soil carbon storage and ecosystem functioning..

Our findings (1) highlight systematic overestimations of large-scale bioenergy potentials in assessments that neglect soil fertility dynamics and (2) suggest that ERW could mitigate a key nutrient bottleneck for tropical bioenergy systems while enhancing the durability and sustainability of biomass-based CDR pathways, linking nutrient management directly to climate policy design.