Chemical and spectroscopic evaluations supporting superior P availability after biochar-P fertilizer application

Sustainable agriculture intensification requires optimization of agriculture resources such as new fertilizers with higher nutrient use efficiency. Biochar has been a promisor alternative not only as a P source but also as a matrix to host P fertilizer to improve its use efficiency by intrinsic features. In our previous work, biochar enriched with P lead to higher sugarcane biomass yield and P use efficiency than conventional P fertilizer in a greenhouse trial, however, the effects of biochar enriched with P in the fate of available-P were not plenty understood. In this work, we investigated the superior P availability after fast-pyrolysis biochar-P fertilizer (BioFert) over the incubation time of 240 days in three distinct soils (sandy, loamy and clayey), evaluating the available-P by an anionic exchangeable membrane (AER) and bicarbonate solution extractions, as also solid P speciation by X-ray Absorption Near Edge Structure (XANES) analysis performed at a Synchrotron source. The AER results showed that available-P in BioFert treatment was, on average, 14% superior in sandy, 56% in loamy, and 72% in clayey soil than triple superphosphate (TSP). XANES results pointed out Al- and Fe-phosphates as the main P-sink for all soils, however both fertilizers introduced P-Ca in the system. The superiority of BioFert was associated with its capacity to buffer the soil pH in values higher than 7 potentially reducing P immobilization. In summary, results support the higher efficiency of BioFert than TSP observed in previous work because it supplies more available P synchronized to plant demand over time.