Soil carbon stocks are highly vulnerable to human activities (such as tillage), which can decrease carbon stocks significantly. These activities break down soil's organic matter and some carbon is converted to carbon dioxide (CO 2). A part of CO 2 (a greenhouse gas that is one of the main contributor to global warming) is lost from the soil by soil respiration (soil CO 2 efflux). The aim of our study is to determine the soil carbon loss by soil CO 2 efflux under different tillage treatments. The experimental site is characterized by continental climate. Field experiment with six different tillage treatments usually used in this area was set up on Stagnic Luvisols in Daruvar, central lowland Croatia in 1994 with investigation aim on determination of soil degradation by water erosion and later, in 2011, expanded to the research on soil CO 2 efflux. Tillage treatments differed in tools that were used, depth and direction of tillage. Tillage treatments were: black fallow (BF), ploughing up/down the slope to 30 cm (PUDS), no-tillage (NT), ploughing across the slope to 30 cm (PAS), very deep ploughing across the slope to 50 cm (VDPAS) and subsoiling (50 cm) plus ploughing (30 cm) across the slope (SSPAS). Field measurements of soil CO 2 concentrations were conducted during one year (n=14) from November 2011 till November 2012, when cover crop was corn ( Zea mays L.). Preliminary soil sampling for determination of soil total carbon content was conducted in April 2011. This paper presents results of soil total carbon content in the soil surface layer (0-30 cm), the variations of CO 2-C efflux during the year, soil carbon loss by CO 2-C efflux and correlation between soil total carbon content and CO 2-C efflux. The range of soil surface total carbon content varied from 19083.7 kg/ha at BF treatment up to 31073.6 kg/ha at SSPAS treatment. The treatment with the lowest average measured CO 2-C efflux was BF. The average CO 2-C efflux at BF treatment was 7.9 kg CO 2-C/ha/day where CO 2-C efflux varied from 2.3 kg CO 2-C/ha/day up to 22.6 kg CO 2-C/ha/day. The treatment with the highest average measured CO 2-C efflux was NT. Range of CO 2-C efflux at NT treatment varied from 7.8 kg CO 2-C/ha/day up to 65.8 kg CO 2-C/ha/day and the average CO 2-C efflux was 24.4 kg CO 2-C/ha/day. Daily soil total carbon loss by soil respiration ranged from 0.04% at BF treatment up to 0.09% at NT treatment. Soil CO 2-C efflux was fully positively correlated with soil total carbon content (r=0.91). After all mentioned, it can be stated that in these agro-ecological conditions, best tillage practice in sustainable plant production in terms of the lowest daily soil total carbon loss (0.06%) by soil respiration is ploughing to 30 cm (PUDS and PAS). Still, it is necessary to conduct the total soil carbon balance in the future research for better understanding of soil carbon gains and losses.
