Influence of Sludge Incineration Ash on Ryegrass Growth and Soil Phosphorus Status

Phosphorus (P) is a limited resource that could be depleted. Consequently, recycling the P contained in sewage sludge, including sewage sludge incineration ash (SIA), from wastewater treatment plants is a possibility to be explored. A greenhouse experiment using annual ryegrass (Lolium multiflorum L.) was performed with an experimental design of three completely randomized blocks of two soils and 29 treatments: one control without P and two levels of 9 and 26 kg total P ha(-1) from 14 different sources: twelve SIAs (not contaminated by trace metals) from the US and Canada, one commercial synthetic fertilizer (triple superphosphate (TSP)), and one commercial rock phosphate (RP). Higher ryegrass biomass levels were achieved at the higher fertilization rate (26 kg total P ha(-1)) and when using the SIAs with the highest P solubility percentage (PSP) (>= 54% of total P). The biomass increases following SIA application were as high as 29% and 59% more than the control for the sandy loam and clayey soil, respectively, but 40% less than in TSP for both soils. A similar behavior was observed for P uptake, with a maximum increase of 26% for the clayey soil, and 165% for the sandy loam soil. The ryegrass biomass and P uptake increases due to SIA application were larger than those due to RP application in the clayey soil, but similar to those in the sandy loam soil. The SIAs with a PSP of >= 54% significantly increased soil available P stocks and saturation. According to our findings, we conclude that the SIAs from municipal and agrifood industries have a potential for P agricultural recycling, but their efficiencies vary.