Differences in Recycled Amendment Phosphorus Solubility and Transport When Interfaced to Soils of Dissimilar Characteristics

ABSTRACT Increasing phosphorus (P) fertilizer use efficiency from bio‐based waste products (i.e., recycled amendments) requires promoting a larger proportion of bioavailable P in soil for plant uptake. Therefore, this study aimed to elucidate how recycled amendment P solubility and movement vary when interfaced with soils of contrasting characteristics. Microcosms were created with a fine‐mesh screen to incubate recycled amendments (iron‐precipitated sewage sludge (sewage), sewage sludge ash (ash), and meat and bone meal (MBM)) with four soils. After 14 or 120 days of incubation, microcosms were destructively sampled. Soil was sliced at the millimetre scale (up to 4 mm) from the interface. Soil P solubility was assessed via water‐extractable P (P w ) and labile P (P lab ; resin plus bicarbonate P), while a sequential fractionation isolated changes to the recycled amendment P pool composition. Results indicated that multiple factors influenced the distance P travelled from the recycled amendment‐soil interface. First, a greater proportion of recycled amendment P lab ensured movement passed the interface. For example, soluble soil P increased far beyond the MBM interface after 14 days. Second, soil characteristics dictated whether recycled amendment P remained soluble after leaving the interface. For example, ash P lab increased and promoted greater travel when incubated with the acidic soil (Orthic Podzol). Finally, time unevenly impacted movement. Sewage P pool composition fluctuated before promoting greater soil transport between the 14‐ and 120‐day incubation. Thus, increasing plant root access to recycled amendment P requires a timed approach that accounts for the physicochemical characteristics of both matrices.