Retention and release of dissolved organic matter in Podzol B horizons

The main objectives were to study the effects of pH on the retention and re lease of organic matter in acid soil, and to determine the main differences in results obtained from batch experiments and experiments in columns. We took soil material from the B horizons of a Podzol at Skanes Varsjo (southe rn Sweden). In batch experiments, soil was equilibrated with solutions vary ing in pH and concentration of dissolved organic C. In Bh samples, the rele ase of dissolved C gradually increased with increase in pH. In the Bs1 mate rial there was a minimum at pH 4.1, and in the Bs2 soil the minimum occurre d at pH 4.6. The ability to retain added dissolved C increased in the order Bh<Bs1 <Bs2. The column experiment was run for 160 days under unsaturated flow condition s. Columns were packed with Bh, Bh+Bs1 or Bh+Bs1 +Bs2 samples to calculate mass balances for each horizon. Solutions either without any dissolved orga nic C or ones containing 49 mg C dm(-3) with pH of 4.0 or 3.6 were used to leach columns. The pH of input solutions only little affected the concentra tion of dissolved C in the effluent. Relative proportions of hydrophobic su bstances decreased with increasing column length and decreasing pH. For inp ut solutions containing dissolved C, near steady state was achieved for bot h the Bs1 and Bs2 horizons with approximately 25% dissolved organic matter retention. Thus, no maximum sorption capacity for dissolved C could be defi ned for these horizons. This behaviour could not have been predicted by bat ch data, showing that column experiments provide useful additional informat ion on interactions between organic compounds and solid soil material.