Aspects of carbon and nitrogen cycling in soils of the Bornhoved lake district .2. Modelling the influence of temperature increase on soil respiration and organic carbon content in arable soils under different managements

Based on field measurements in two agricultural ecosystems, soil respiration and long-term response of soil organic carbon content (SOC) was modelled. The model predicts the influence of temperature increase as well as the effects of land-use over a period of thirty years in a northern German glacial moraine landscape. One of the fields carried a maize monoculture treated with cattle slurry in addition to mineral fertilizer (''maize monoculture''), the other was managed by crop rotation and received organic manure (''crop rotation''). The soils of both fields were classified as cambic Arenosols. The soil respiration was measured in the fields by means of the open dynamic inverted-box method and an infrared gas analyser. The mean annual soil respiration rates were 268 (maize monoculture) and 287 mg CO2 m(-2) h(-1) (crop rotation). Factors controlling soil respiration were soil temperature, soil moisture, root respiration and carbon input into the soil. Q(10)-values of soil respiration were generally higher in winter than in summer. This trend is interpreted as an adaptive response of the soil microbial communities. In the model a novel mathematical approach with variable Q(10)-values as a result of temperature and moisture adjustment is proposed. With the calibrated model soil respiration and SOC were calculated for both fields and simulations over a period of thirty years were established. Simulations were based on (1) local climatic data, 1961 until 1990, and (2) a regional climate scenario for northern Germany with an average temperature increase of 2.1 K. Over the thirty years period with present climate conditions, the SOC pool under ''crop rotation'' was nearly stable due to the higher carbon inputs, whereas about 16 t C ha(-1) were lost under ''maize monoculture''. Under global warming the mean annual soil respiration for both fields increased and SOC decreased by ca. 10 t C ha(-1) under ''crop rotation'' and by more than 20 t C ha(-1) under ''maize monoculture''. It was shown that overestimation of carbon losses in long-term prognoses can be avoided by including a Q(10)-adjustment in soil respiration models.