The impact of non-grain conversion of cultivated land on the relationship between agricultural carbon supply and demand

Increasing carbon sinks and reducing emissions in agricultural system is important for global sustainable development. Affected by the increasing cost and the declining profit of grain planting in China, the overall agricultural planting structure in the Northwest region showed a trend of conversion to non-grain crops. However, the impact of the non-grain conversion of cultivated land on agricultural carbon supply and demand is unclear. Therefore, taking Gansu Province as an example, this paper constructed a theoretical framework for the impact of non-grain conversion on agricultural carbon supply and demand, and empirically tests the relationship between non-grain conversion and carbon supply and demand index using a two-way fixed effects model based on statistical panel data from 2000 to 2020. The study found that the proportion of non-grain crop planting areas in the Gansu Province increased from 24.88% to 32.90% from 2000 to 2020. The proportion of non-grained medium and high value areas increased significantly and spread from a localized to a province-wide influence. In the past 21 years, the total agricultural carbon absorption showed an inverted “N” type downward development trend and was greatly affected by the carbon absorption of grain crops (especially wheat, corn), while the total agricultural carbon emission showed an “N” type upward trend and was greatly affected by the carbon emissions of non-grain crops (especially vegetables). The increase in the area of non-grain crops weakened the carbon sink effect of farmland and intensified its carbon source properties, resulting in a decrease in the carbon supply-demand index (SDIC) from 0.187 to 0.023. The rate of non-grained level (NGL) is significantly negatively correlated with the SDIC, and that for every 1% increase in the NGL, the SDIC will decrease by 0.728%. Based on this, policy recommendations for optimizing planting structures and agricultural practices are proposed with a view to providing theoretical support for achieving a win-win situation for food security and ecological safety in Gansu Province.