Direct experimental evidence for the contribution of lime to CO 2 release from managed peat soil

Abstract

Liming is a common management practice used to achieve optimum pH for plant growth in agricultural soils. Addition of lime to the soil, however, may cause CO 2 release when the carbonates in lime dissolve in water. Although lime may thereby constitute a significant carbon source, especially under acidic soil conditions, experimental data on the CO 2 release are lacking so far. We conducted a split-plot experiment within a cut-away peatland cultivated with a bioenergy crop (reed canary grass, Phalaris arundinacea L.) with lime and fertilizer treatments to determine effects of lime on the CO 2 emissions from soil and to better understand mechanisms underlying liming effects. Carbon dioxide release was measured over two growing seasons in the field after liming, and complementary laboratory studies were conducted. To differentiate CO 2 derived from lime and biotic respiration the δ 13C of CO 2 released was determined and the two-pool mixing model was applied. The results showed that lime may contribute significantly to CO 2 release from the soil. In the laboratory, more than 50% of CO 2 release was attributable to lime-carbonates during short-term incubation. Lime-derived CO 2 emissions were much lower in the field, and were only detected during the first (2–4) months after the application. However, a maximum of 12% of monthly CO 2 emissions from the cultivated peatland originated from the lime. Biotic respiration rates were similar in limed and unlimed soils, suggesting that higher pH did not, at least in the short-term, increase carbon losses from cultivated peat soils. Additional fertilization and acidification did not contribute to further CO 2 release from the lime. According to our first estimations about one sixth of the lime applied would be released as CO 2 from the managed peatland, with all lime-derived emissions occurring during the first year of application (equivalent to about 4.6% of the total annual CO 2 losses from the soil in the first year). This suggests that the mass-balance approach as proposed by the IPCC Tier 1 methodology, which assumes that all carbon in lime ends up as CO 2 in the atmosphere, overestimates the emissions from lime. Our study further shows that there is a great risk to overestimate heterotrophic microbial activity in limed soils by measuring the CO 2 release without separating abiotic and biotic CO 2 production.