Fate of sludge phosphorus in soil-plant systems

Although sewage sludges have been used for many years as sources of P for agricultural crops, there is a lack of information regarding the proportion of sludge P that can be used by crops. This work was carried out to assess the importance of soil available P and sludge origin on the utilization of sludge P by plants. First, the changes in soil P isotopically exchangeable within 1 min (E1 min) were measured in incubated soil-sludge mixtures using two soils and four sludges. The uptake of sludge P by ryegrass was also measured on the same sludge-amended soils. Results indicate that the origin of the sludge and the soil available P content must be taken into account when advising sludge application to crops to adjust P inputs to plant needs.