Phosphorus recycling from wetland filters and other wastes

The plant P uptake from wetland filters, sewage sludge and biochar was investigated in pot experiments after manipulating the P-rich waste pH by mixing with other wastes giving an acidic reaction and low pH (organic acid, compost leachate) or a high pH (concrete waste, lime) at two levels, all with three replicates. Pots with no fertilizer and with mineral fertilizer served as controls. Available P measured both with passive DGT samplers and by P uptake in rye grass during multiple harvests over the experimental periods was the factor studied. The treatment pH in waste was about or Jess than 4 in the acid treatment, and more than 11 in the high pH treatment. The pH in the pots during grass production was approximately 6.5. The P uptake measured in the grass increased up to 56 % after pH treatment of the waste. The P uptake responded both to the high and low pH treatments, probably due to the prevalence of different P chemical species. The more extreme pH treatments gave the highest uptake. The DGT uptake gave the same broad picture in the pots fertili zed with biochar but not in pots with sludge, and also without the separation between high and low treatments. The passive samplers correlate relatively well with the measured grass uptake