As cropland possess dual carbon effects of emitting and sequestering, giving full attention to its net carbon sequestration is an effective option for mitigating global warming. By analyzing the carbon cycle of a cropland use system, we develop an inventory for measuring the net carbon sequestration, covering four carbon sources, i.e., agricultural materials, rice fields, soils, straw burning, with the crop carbon sequestration considered. Different from conventional studies that have focused on quantity, in this study, we define net carbon sequestration performance of cropland use (NCSPC) as the ratio of actual net carbon sequestration to an optimal value per unit of cropland. We estimate the net carbon sequestration of cropland use, from 2000 to 2019, for the study area consisting of the 13 principal grain-producing provinces in China. Then, global-SBM is applied to measure the provincial NCSPC; furthermore, the Theil index and convergence test are employed to portray the spatiotemporal characteristics and regional divergence. The results show the following: (1) The net carbon sequestration was 3.837 t per hectare of cropland in the principal grain-producing area, of which the sequestration and the emission were 6.343 t and 2.506 t, respectively. The share of emissions, from largest to smallest, was methane from rice paddies, agricultural materials, straw burning, and soil nitrous oxide. Specifically, cropland use in Henan exhibited the strongest net carbon sequestration, whereas in Hunan it was the lowest. (2) The average NCSPC was 0.774 in the principal grain-producing area, indicating that 22.6% of the net carbon sequestration per unit of cropland remained to be explored under the corresponding production technology and input combinations. Temporally, the NCSPC had an annual change rate of −0.30%, displaying a slowly declining trend. Spatially, the NCSPC evolved from a scattered distribution to blocky agglomeration, eventually presenting a decreasing pattern from north to south. (3) First, the total Theil index increased, and then decreased, indicating that the regional disparity of the NCSPC expanded early but shrank later. From 2011 to 2019, inter-regional disparity took up more in the total. Over time, both the whole region and the subregions obeyed the σ convergence. Unlike the benign trends observed in Zones I and II, the NCSPC values of Zone III converged to a low level. This study aims to provide a theoretical base for emission mitigation and sequestration promotion for cropland use.

Assessing the emission-peaking process of agricultural land use provides valuable insights for mitigating global warming. This study calculated agricultural land-use carbon emissions (ALUCEs) in China from 2000 to 2020 and explored the peaking process based on quantitative criteria. Further, we applied the Tapio decoupling index and environmental Kuznets curve (EKC) model to discuss the robustness of the peaking process. The main conclusions are as follows: (1) From 2000 to 2020, China’s average ALUCEs were 368.1 Mt C-eq (1349.7 CO₂-eq), peaking at 396.9 Mt C-eq (1455.3 Mt CO₂-eq) in 2015 before plateauing. Emissions from agricultural materials and soil management had entered the declining period, while those from rice cultivation were in the peaking period, those from straw burning were still rising, and those from livestock breeding remained at the plateauing phase. (2) The provinces of Beijing, Tianjin, and nine others saw a decline in ALUCEs, while Hainan, Guizhou, and another nine provinces observed plateauing, and Ningxia, Qinghai, and six other provinces experienced peaking. (3) Decoupling analysis confirmed that emission-peaking states remained stable even with agricultural growth. Instead of an inverted U-shaped relationship, we found an N-shaped relationship between ALUCEs and agricultural GDP. The spatial EKC model indicated that the peaking process had spillover effects between provinces. It is recommended that China accelerate ALUCE mitigation based on the source and phase of emissions, considering the peaking process and magnitude.

An analysis of carbon emissions of crop production provides paths for global warming mitigation. Existing studies have focused on the magnitude of the carbon emissions from crop production, which is unreasonable for inter-location comparison due to neglecting regional variations in cultivation technologies and planting scale. Different from the conventional idea, this paper estimated the carbon-emission density of crop production (CEDCP) based on carbon emissions per hectare of crop production. With the 30 Chinese provinces between 2000 and 2020 as the study area, temporal dynamics and spatial patterns of the CEDCP were explored, regional disparities of the CEDCP were discussed based on the Theil index, and the possibility of regional coordinated optimization for the CEDCP was explored by relying on the convergence tests. The results show that the average annual CEDCP in China was 1.462 t/hm², reaching a peak of 1.576 t/hm² in 2015. The national carbon-emission densities of agricultural materials, rice fields, soil management, and straw burning were 0.492 t/hm², 0.390 t/hm², 0.189 t/hm², and 0.391 t/hm², respectively. In many provinces, the CEDCP increased first and then decreased, presenting a spatial pattern of high in the eastern region and low in the western region. Regional disparities of CEDCP shrank early but expanded later, and the disparities within the western region had always contributed considerably to the overall disparities. The CEDCP had shown σ- and β- convergence in both national and regional scales, and the convergence process had positive spillover effects. These findings suggest that inter-provincial cooperation may facilitate the CEDCP to converge.