Based on the statistic data of crop yield

planting area

effective irrigation area

fertilizer usage and agricultural machinery power of Hebei Province from 1989 to 2008

the carbon source and sink of the farmland ecosystems in Hebei Province were estimated.Furthermore

the temporal and spatial variations and the influencing factors of carbon source and sink were analyzed.The results showed that the total carbon sequestration and emission of the farmland ecosystems in Hebei Province showed a gradually rising process in the last 20 years

and more carbon was sequestrated than emitted.Overall

the farmland ecosystem of Hebei Province was a carbon sink.Spatially

the density of carbon sink declined from southeast to northwest.The carbon sequestrated by wheat and corn plants accounted for the largest proportion.In addition

the process of agricultural irrigation was the main controlling factor for carbon sequestration.The carbon emitted from fertilizers contributed the biggest proportion among the three major carbon emission sources of the farmland ecosystems.