Keywords: Biosolids, diffusive gradient in thin films, organo-mineral fertiliser, OMF, phosphorus, ryegrass, sewage sludge
Sewage sludge recycling can be an important source of phosphorus (P) in agricultural systems. The purpose of this study was to investigate the role of organo-mineral fertilisers (OMF) derived from sewage sludge in reducing agricultural demand for phosphorus. A field trial was established to investigate the influence of OMFs on phosphorus dynamics, optimal application rates for ryegrass yield, and the potential for phosphorus accumulation. The results were compared to application of urea and biosolids as a fertiliser. Diffusive gradient in thin films (DGT) and the more conventional Olsen-P method were used to observe phosphorus. It is considered that the DGT method better reflects the bioavailable P fraction. Comparison of the two methods showed a significant positive correlation (R2 = 0.63). Soil analysis of pre-fertiliser application showed that both the OMF and urea fertiliser plots had lower P levels than the control and biosolid plots. Post-harvest there was reduction of P as determined by the Olsen method where urea had been applied. This reduction was not observed in the DGT results. Differences between Olsen-P and DGT methods observed after urea application may be the result of different P pools being observed. Results indicate that DGT data may be a better indicator of plant available P than Olsen-P and thereby its use may avoid unnecessary application of phosphorus fertiliser.
M Pawlett, R Sakrabani, R Read, L K Deeks and S Tyrrel, Department of Environmental Science and Technology, Cranfield University, Cranfield, Bedfordshire, MK43 0AL, UK.
M S Le, United Utilities Group plc, Lingley Mere Business Park, Warrington, WA5 3LP, UK.
18 pages, 5 figures, 1 table, 18 references.