Availability of Cu and Zn in an acidic sludge-amended soil as affected by zeolite application and liming

Purpose Acidic soils exhibit high trace element availability compared to neutral pH soils, and thus, when trace metals are added (e. g. due to sewage sludge application), measures should be taken to reduce their mobility. In this experiment, we tested two such methods, liming and zeolite addition. The aim was to measure the availability, in ryegrass (Lolium perenne L.), of heavy metals (Cu and Zn) added to soil with sewage sludge in both acidic and limed soil. Materials and methods Thus, in this pot experiment, we used a soil at two pH values (original soil at pH 3.56 and limed to 6.5), two rates of sewage sludge (0 and 50 Mg ha(-1)) and three rates of zeolite (0, 2 and 5 Mg ha(-1), referred to as Z-0, Z-1 and Z-2, respectively). Results and discussion We found that metal concentrations in plant decreased significantly with liming but zeolite did not further reduce metal levels. In metal extractions with DTPA, zeolite additions reduced metal concentrations. In the second sampling time (on day 100), metal levels were significantly reduced at Z-0 and Z-1 compared to day 50, but at Z-2, metals were either only slightly reduced or even unchanged. Conclusions We concluded that zeolite hindered metals from being strongly and irreversibly bound onto soil colloids. Zeolite at Z-2 kept metal availability relatively high over time, while metal availability at Z-0 and Z-1 was being reduced due to liming.