Effect of liming on microbial biomass carbon of acidic arenosols in pot experiments

In the paper we investigate the effect of liming on the microbial biomass carbon (MBC) in pot experiments during two vegetation periods. There was also another goal to get better understanding of the role of dissolved organic matter (DOM) and its quality on microbial processes. Pot experiments were carried out on two acidic soils. Liming material treatment was 0, 1, 2, 3 g CaCO3 /kg soil (corresponding with 0, 1.4, 2.8, 4.1 t CaCO3 /ha, respectively). On both soils, 3-3 soil samples were taken for two growing periods and the substrate-induced respiration (SIR), dissolved organic carbon and nitrogen (DOC and DON), and soil pH were determined from the soil samples. The SIR can be used to characterize the active biomass within the total microbial biomass. Liming was found to increase soil respiration and consequently MBC in the first year of the experiment, but at the maximum lime rate these values stagnated or declined in many cases on each soil. In the second year, the effects of treatments were much lower both on Kisvarda and on NyMugos soils. Under the given experimental conditions, when the DOC/DON ratio rose to above 30-40, disturbances appeared in N supplies to microorganisms. The N content of the easily mineralisable organic matter in the soil became so low that it inhibited the reproduction of the microorganisms.