Winter wheat carbon exchange in Thuringia, Germany

Eddy covariance measurements and estimates of biomass net primary production (NPP) in combination with soil carbon turnover modelled by the Roth-C model were used to assess the ecosystem carbon balance of an agricultural ecosystem in Thuringia, Germany, growing winter wheat in 2001. The eddy CO 2 flux measurements indicate an annual net ecosystem exchange (NEE) uptake in the range from −185 to −245 g C m −2 per year. Main data analysis uncertainty in the annual NEE arises from night-time u ∗ screening, other effects (e.g. coordinate rotation scheme) have only a small influence on the annual NEE estimate. In agricultural ecosystems the fate of the carbon removed during harvest plays a role in the net biome production (NBP) of the ecosystem, where NBP is given by net ecosystem production (NEP=−NEE) minus non-respiratory losses of the ecosystem (e.g. harvest). Taking account of the carbon removed by the wheat harvest (290 g C m −2), the agricultural field becomes a source of carbon with a NBP in the order of −45 to −105 g C m −2 per year. Annual carbon balance modelled with the Roth-C model also indicated that the ecosystem was a source for carbon (NBP −25 to −55 g C m −2 per year). Based on the modelling most of carbon respired resulted from changes in the litter and fast soil organic matter pool. Also, the crop and management history, particularly the C input to soil in the previous year, significantly affect next year’s CO 2 exchange.