The net carbon effect of farming is crucial for climate change mitigation, yet there is insufficient research on the impact of land management scale on it in China. This study aims to explore the magnitude and role of land management scale on the net carbon effect of farming at the spatial level, including threshold characteristics. Unlike previous studies focused on the domestic agricultural economy, this study employs ecological findings to calculate carbon sinks and certain carbon emissions. The carbon-balance ratio is used to characterise the net carbon effect of farming. The spatial Durbin model and threshold regression model were utilised with a sample of 30 provincial-level regions in China from 2004 to 2019. The results indicate that national farming generally exhibits a net sink effect, with significant interannual fluctuations. After applying robust standard errors, the expansion of the land management scale significantly increases sinks and reduces emissions, and it has a positive spatial spillover effect on the carbon-balance ratio, demonstrating significant spatial heterogeneity. Furthermore, as the land management scale expands, the influence of rural residents’ income and education level on the carbon-balance ratio changes direction, showing significant non-linear relationship characteristics.

The impact of the agriculture net carbon effect is crucial for climate change mitigation, yet research on this topic in China is currently insufficient. In this study, the carbon balance ratio (CBR) is used to characterise the net carbon effect of agriculture, and the spatial Durbin model and threshold regression model were used to empirically analyse the CBR with a sample of 30 provincial-level regions in China from 2004 to 2019. The aim was to investigate the mechanism of the influence of the land management scale (SCALE) of farming on the CBR. The results of the study indicate that national farming generally has a net sink effect, with large changes in interannual fluctuations; the expansion of SCALE has an obvious role in increasing sinks and reducing emissions, and has a positive spatial spillover effect on CBR, with significant spatial heterogeneity. Furthermore, as the SCALE expands, the direction of the influence of rural residents’ income and education level on CBR changes in the opposite direction, showing a significant non-linear relationship characteristic. However, in most areas, the SCALE threshold has not yet been reached, suggesting that the improvement in education levels can still offset the negative impact of economic income growth in the short term. The study recommends paying attention to the role of farmers’ human capital, changing production methods, and implementing carbon peaking and carbon neutrality goals to enhance the net sink effect of the farming industry, which would be achieved by increasing land management scale.