Objective The carbon footprint of agriculture contributes to the measurement of "carbon" in agricultural production and characterizes sustainable agriculture with a relative balance between crop yields, soil productivity and environmental quality. Research on the carbon footprint of food crop production processes has a very important role and significance in promoting low-carbon agriculture and formulating locally adapted and sustainable development strategies.

Method Through the life cycle assessment method, the black soil farmland carbon emissions of major grain crops (rice, corn, soybean) in the cities of the three provinces (Heilongjiang, Jilin and Liaoning) in Northeast China from 2011 to 2020 were accounted, and the factors affecting the carbon footprint of farmland in each province were analyzed.

Result The results showed that among the carbon footprint per unit of production and carbon footprint per unit area of the three major food crops during the period from 2011 to 2020, rice had the highest carbon footprint, with mean values of 0.68 kg CO₂-eq/kg⁻¹ and 4.6 t CO₂-eq/hm⁻², respectively. While soybeans had the lowest carbon footprint per unit of area, and maize had the lowest carbon footprint per unit of production. The differences in carbon footprint levels among the three provinces were more obvious, the highest carbon footprint per unit of rice and corn production in Heilongjiang Province, and he highest carbon footprint per unit of soybean production in Jilin Province. All three major crops in Heilongjiang Province had the lowest performance in carbon footprint per unit of area. In terms of the spatial distribution of carbon emissions from the production of major grain crops in the three provinces, Harbin City and its surrounding municipalities were the main areas of carbon emissions. Fertilizer inputs and the associated carbon emissions accounted for the largest proportion of the carbon footprint composition of grain crop production.

Conclusion Improving the efficiency of fertilizer use, optimizing the types of fertilizers, reforming fertilizer application methods, reconciling the growing mechanization of agriculture with the consequent increase in carbon emissions caused by fuel oil and electricity, will be the keys to reduce carbon emissions in the northeastern black soil region and achieve the dual-carbon goal.