Phosphorus availability in different types of open-cast mine spoil and the potential impact of organic matter application

Greenhouse experiments were conducted in order to determine for carboniferous and non-carboniferous mine spoil substrates from the Lusatian lignite mining area (i) the suitable extraction method for plant available P, (ii) the soil capacity for immobilisation of P and (iii) the impact of sewage sludge and compost on P availability. Ca-lactate extraction (DL) and NH₄F-extraction (Bray) were both suited equally well for the determination of plant available P as they extracted similar amounts of P on both spoils, they showed a close correlation with each other (R=0.97 ²) and they showed a close relation with plant P uptake (R²=0.63 and R²=0.66, respectively). Phosphorus recovery from limed carboniferous mine spoil five days after mineral fertiliser application was only 50%, and decreased to 30% after 54 days. As pH was increased from 3.0 to 5.0 the amount of P immobilised decreased only by about 5%. Several pH dependent processes of P immobilisation and release could occur concurrently counteracting each other. One process could be P sorption to newly formed hydroxy-Al-surfaces but P desorption could also take place as pH increases by decreasing surface positive charge. Finally, due to high Ca concentrations in spoil solution formation of Ca-phosphates, even at lower pH values, cannot be excluded as a possible mechanism of P immobilisation. As part of the P is bound in organic matter, application of P with organic matter resulted in a lower P recovery compared to mineral P-fertiliser. However, the amount of P recovered did not differ between carboniferous and non-carboniferous mine spoil, if P was applied in the form of organic matter, indicating that the application of P with organic matter might be a measure to overcome P immobilisation in carboniferous mine spoils. This revised version was published online in June 2006 with corrections to the Cover Date. This revised version was published online in June 2006 with corrections to the Cover Date. This revised version was published online in June 2006 with corrections to the Cover Date.