Objective In recent years, carbon footprint analysis has been widely applied to the assessment of carbon sources/sinks in farmland ecosystems, but Chinese prefecture and municipal level studies still have problems such as narrow time span and lack of measurement of key processes (e.g., N₂O emissions from farmland, CH₄ release from rice paddies, and soil respiration and sequestration), which lead to bias in the assessment of regional carbon sources/sinks and constrain the precise implementation of the “dual−carbon” policy. This study aims to reveal the time−series evolution of carbon sources/sinks in farmland ecosystems in Heihe City, Heilongjiang Province, over a 40−year period (1984—2023), to quantify the potential of carbon sinks to contribute to carbon neutrality, and to identify the dominant factors of carbon footprints, so as to provide data support for the local government to realize the goal of “dual−carbon”.

Methods Based on the statistical data of crop sown area, production and agricultural inputs in Heihe City during the 40−year period (1984—2023), and utilizing the carbon footprint model of agricultural ecosystems, we comprehensively assessed the total amount of carbon sources/sinks of agricultural ecosystems in Heihe City, as well as the contribution index of carbon sinks in the region.

Results ①The carbon emissions from farmland ecosystems in Heihe City from 1984 to 2023 showed a continuous growth trend, with an average annual growth rate of 2.84%. During this period, both carbon absorption and carbon footprint showed a fluctuating upward trend, but the total amount of carbon absorbed was much higher than the total amount of carbon emitted, and the ratio of the two was at the level of 2.59∶1. ② From the perspective of carbon emission structure, soil respiration and farmland N₂O emission are the main sources of carbon emission, accounting for 58.80% and 32.22% respectively; chemical fertilizer, pesticide application and agricultural irrigation account for a significant proportion of carbon emission from inputs of agricultural means of production (74.51%, 12.26%, and 8.66%), although the proportion of carbon emission generated by the use of agricultural film is relatively low (1.33%), it still needs to be paid enough attention.③The amount of carbon absorbed by farmland ecosystems is mainly related to the type of crops and their yields, with grain crops and soil constituting the bulk of farmland carbon sinks, accounting for 84.08% and 10.10%, respectively, of which soybean, corn, and wheat are the main carbon absorbing crops, contributing to 80.83% of the carbon absorption in the Heihe region. ④The carbon footprint of farmland ecosystems in Heihe City accounted for a slightly lower proportion of the cultivated area in the same period (28.80%~66.44%), and the carbon sink capacity of agroecosystems in the region was stronger.

Conclusions The farmland ecosystem in Heihe City shows a carbon surplus and plays a good role as an ecological barrier, but in the future, it is still necessary to deepen the “three reductions” in agriculture and improve the function of carbon sinks, so as to synergistically promote the goal of Carbon Peaking and Carbon Neutrality Goals and the high−quality development of the region.