Soil respiration after tillage under different fertiliser treatments - implications for modelling and balancing

Temperature-driven models of soil respiration (SR) are crucial for estimating C-balances of arable soils. However, model construction may be severely influenced by tillage operations. The impact of tillage on the temperature dependence of SR was studied to reveal the temporal patterns of model quality of temperature-driven SR-models. To obtain SR, CO ₂ fluxes were measured with a dynamic chamber technique in treatments of an energy crop rotation amended with biogas residues (BR) and mineral fertiliser (MF). Measurements were performed with short intervals during the first three days after tillage operations, then with extending intervals between measurements up to 35 days after tillage. Additionally, soil concentrations of hot-water extractable organic carbon (HWC) were determined before and during the experiment. Overall, in all treatments individual CO ₂ fluxes were affected by the extent of soil disturbance and fertiliser treatment. The highest tillage-induced fluxes where observed after disking in MF treatment. Tillage also induced an immediate increase of HWC, indicating additional labile C and a fast response of microbial activity. However, the change of HWC lasted only one day and approximated the pre-tillage values within a week. Even though BR soil had a higher HWC content, the increased C mineralisation in one repetition of MF suggests that buried plant residues might have a higher influence on SR after tillage than the type of fertiliser. Directly after soil disturbance by tillage it was impossible to construct temperature-driven models for SR in all treatments. Assuming that the coefficient of determination is appropriate with R ²≥0.5 and the model quality is good with NRMSE≤0.15, the qualities of the models increased continuously with time, but were unsatisfying for at least two weeks. During this time, SR showed a high sensitivity to changing environmental influences like precipitation and soil moisture or available C for microbial turnover, rather than temperature. The treatment BR showed a less sensitive pattern, which might be attributed to an altered soil structure and microbial activity of soil after long-term application of an organic fertiliser like BR. Therefore, temperature-driven models for the prediction of soil derived CO ₂ emissions should be applied carefully for the days and weeks after tillage and verification by measurements in shorter intervals is advisable.