Influence of dolomitic lime on DOC and DON leaching in a forest soil

The influence of liming on leaching and distribution of dissolved organic c arbon (DOC) and nitrogen (DON) in mineral soil was investigated in a leachi ng experiment with soil columns. Soil samples from separate horizons (O, A and B horizons) were collected from control and limed plots in a field limi ng experiment in a spruce forest in southern Sweden. The field liming (0.88 kg(-2)) had been carried out 8 years before sampling. To minimize the vari ation among replicates, soil profiles were reconstructed in the laboratory so that the dry weight was the same for each individual soil horizon regard less of treatment. Two soil column types were used with either the O+A hori zons or the O+A+B horizons. One Norway spruce seedling (Picea abies (L.) Ka rst) was planted in each soil column. Average pH in the leachate water was greater in the limed treatment than in the control treatment (5.0 versus 4. 0 for O+A columns and 4.3 versus 3.8 for O+A+B columns). After reaching an approximate steady state, the leaching of DOC was 3-4 times greater from th e limed O+A and O+A+B columns than from the corresponding control columns b ut the leaching of DON increased (3.5 times) only in the limed O+A columns. There was a significant correlation between DOC and DON in the leachates f rom all columns except for the control O+A+B columns, which indicated a dec oupling of DOC and DON retention in the B horizon in the control treatment. This might be explained by a selective adsorption of nitrogen poor hydroph obic compounds (C/N ratio: 32-77) while there was a lower retention of nitr ogen rich hydrophilic compounds (C/N ratio: 14-20). Proportionally more hyd rophobic compounds were leached from the limed soil compared to the unlimed soil. These hydrophobic compounds also became more enriched in nitrogen af ter liming so in the limed treatment nitrogen might be adsorbed at nearly t he same proportion as carbon, which might explain the fact that there was n o decoupling of leached DOC and DON from the B horizon after liming.