Evolution Characteristics of Agricultural Planting Structure in Northeast China (1950–1980) and Implications for Agricultural Carbon Emission Estimation

Agricultural carbon emissions, a key part of terrestrial carbon emissions, affect global carbon accounting, with historical data scarcity adding to calculation difficulty. Exploring agricultural planting structure evolution can supplement historical data and improve accounting accuracy. Based on local chronicles and statistics, this study reconstructs Northeast China’s planting structure of six major crops during the 1950s–1980s via threshold classification and transfer matrix methods. Results show high-carbon crops (corn in particular) expanded notably, while low-carbon crops (especially sorghum) declined. Planting patterns varied regionally, with the most complex structural changes occurring in the 1960s–1970s. Agricultural carbon emissions fluctuated in phases; the planting scale effect dominated emission growth, the intensity effect inhibited it, and the structural effect played a heterogeneous auxiliary role. This study provides a historical basis for low-carbon agricultural planning and differentiated carbon reduction policies.