Data sets of biometeorological measurements of ecosystem CO2 flux, combined with harvest and manure data from several European cropland were integrated to provide an assessment of the carbon budget. Sites encompassed different climatic regions and contrasting crop rotations. The influence of different crops and management practices was also assessed to identify some of the major factors contributing to the cropland carbon balance. Since crops are rotated and cropping periods do not always follow the calendar year, net ecosystem production (NEP) as well as net biome production (NBP) sums of full crop rotations or of at least 4 years of longer-term crop rotations and of monocultures were used. In a second analysis NBP sums were correlated to soil properties. Finally, the data were combined with additional data to derive a mean annual GHG balance for the European cropland sites under consideration.