Plant Availability of Phosphorus From Sewage Sludge Ash‐Based Fertilizers and Its Relationship to Phosphorus Extractability
Kai Leers, Ute Arnold, Hannes Herzel, Christian Adam, Jürgen BurkhardtABSTRACT
Background
Sewage sludge ash (SSA) is a potential phosphorus (P) source for fertilizers, but untreated SSA (USSA) often shows low plant availability of P. To increase P availability, sodium additives can be applied before sewage sludge incineration or during thermochemical SSA posttreatment, as this leads to the formation of CaNaPO 4 .
Aim
Investigation of the plant availability of P from SSA‐based fertilizers and its predictability by chemical extraction methods.
Methods
Two USSAs, one thermochemically post‐treated SSA using sodium additives, three SSAs produced from sewage sludge, to which different amounts of sodium additives were added before incineration, and triple superphosphate (TSP) were used as P fertilizers in a pot experiment with spring wheat grown on a sandy soil. The fertilizers were applied in three doses (20, 40, or 60 mg P kg −1 fine soil) and were compared to a Zero P control. Six fertilizer and two soil extraction methods were used to investigate the relationship between plant availability of P and its extractability.
Results
P from SSA‐based fertilizers was not water‐soluble but showed increased P extractability, for example, with neutral ammonium citrate (NAC), and increased plant availability due to the treatments. The performance of USSA (NAC ≤ 35%) was low at all P doses, whereas the treated, highly soluble SSAs (NAC > 90%) were as effective as TSP at all P doses. The performance of products with NAC extractabilities of 49% and 80% tended to increase with increasing P dose.
Conclusion
Thermochemical treatment of sewage sludge or SSA with sodium additives increases plant availability of P, as also indicated by P extraction methods.