Biotic strategies to increase plant availability of sewage sludge ash phosphorus

Sewage sludge incineration‐ash (FB‐I) represents a potential alternative phosphorus (P) fertiliser with a high concentration of P, although with relatively low crop availability. In this study, we investigated two P‐solubilisation approaches (acidification and P mobilisation by citrate) to enhance plant P uptake from the FB‐I ash in a pot study by using various biotic strategies: (1) a pre‐treatment of ash with a Penicillium bilaiae inoculum, (2) an isogenic line of wheat that excretes citrate from the root tip, (3) nitrogen (N) provided as urn:x-wiley:14368730:media:jpln201800154-math-0001 combined with nitrification inhibitor dicyandiamide (DCD). All strategies were tested combined with each other and with different methods for ash application: (1) completely mixed within the top one third of soil in a pot, or (2) applied as distinct band at 10 cm depth. Triple super phosphate (TSP) at a rate of 15 mg P kg−1 soil per pot was sufficient to support maximum shoot growth. Ash mixed into the first top third part of soil in the pot at a rate of 180 mg P kg−1 soil (equivalent to 60 mg P kg−1 soil throughout the pot) significantly increased the soil water‐extractable P and the subsequent shoot P uptake and shoot biomass for both wheat lines and microbial pre‐treatment to support maximum plant performance. Shoot P concentration in these treatments was further enhanced when the plants received urn:x-wiley:14368730:media:jpln201800154-math-0002 and DCD, although not leading to a significant increase in shoot biomass. The citrate secretion by the root tips and pre‐inoculation with P. bilaiae of the ash did not influence plant growth. In conclusion, root‐zone soil acidification by urn:x-wiley:14368730:media:jpln201800154-math-0003 nutrition is regarded as a promising strategy to improve the fertilising effect of such alternative P fertilisers originating from urban waste streams.