The Fate of Sludge Phosphorus in Soil-Plant Systems
1996
Frossard, E. | Sinaj, S. | Zhang, L-M | Morel, J. L.
Sewage sludges have been used for many years as sources of P for agricultural crops, but there is a lack of information regarding the proportion of sludge P that can be used by crops. The aim of this work was 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 (E1min) were measured in incubated soil-sludge mixtures using two soils and four sludges. Then, the uptake of sludge P by ryegrass (Lolium perenne L.) was measured on the same sludge-amended soils. The application of sludges increased E1min to values lower or equal to those obtained following the application monocalcium phosphate. Similarly the utilization of sludge P by ryegrass was systematically lower than the utilization of P derived from a water-soluble fertilizer. In both soils, the lowest utilization of sludge P was observed for the two FeSO₄ flocculated and anaerobically digested sludges, while the primary sludge and the aerobically digested sludge released somewhat higher quantities of P to ryegrass. In the clayey soil, the amount of sludge P taken up by the crop was significantly related both to the sludge and soil available P content, whereas no such relation was observed in the loamy soil because of its high available P content. The origin of the sludge and the soil available P content must therefore be taken into account when advising sludge application to crops to adjust P inputs to plant needs.
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