Optimizing crop production toward agricultural carbon neutrality in China

Crop production is strategic for food security and climate change mitigation, and can provide a temporary soil carbon sink. There is an ongoing debate about how to optimize crop production in China toward carbon-neutral agriculture. This paper summarizes major carbon budgets in staple crop production in China over recent decades, synthesize reported impacts of available and developing field management practices on greenhouse gas emissions reduction and carbon sink increase. According to recent studies, cropland-based GHG emissions (55% N2O and 44% CH4) increased at a rate of 4.3 Tg·yr–1 CO2-eq from 1990 to 2015 and peaked at 400 Tg CO2-eq in 2015. Subsequently, there was a substantial decrease of 11.6 Tg·yr–1 CO2-eq between 2015 and 2021. A similar bell-shape trend has been observed in yield-scaled GHG emission intensity over the years for cereals excluding rice, as rice exhibited a steady decline in yield-scaled emission intensity since 1961. For soil C in Chinese cropland, topsoil C represents a huge C pool, containing 5.5 Pg of soil organic carbon (SOC) and 2.4 Pg of soil inorganic carbon (SIC). However, these densities are relatively low globally, indicating a high C sequestration potential. Soil C in cropland has been a weak sink of 5.3 Tg·yr–1 C in China since the 1980s, resulting from the net effect of SOC sequestration (21.3 Tg·yr–1 C) and SIC loss (–16 Tg·yr–1 C), which only offsets 5.7% of simultaneous cropland GHG emissions. Hence, cropland remains consistent and significant GHG sources, even when considering soil C sequestration and excluding related industrial and energy sectors. Fortunately, many reliable management practices have positive effects on emission intensity of crop production, in terms of fertilizer application, irrigation and tillage. However, the path to achieving carbon neutrality in China’s cropland is still uncertain and requires further quantitative assessment. Nonetheless, this synthesis highlights that the huge potential, and strong scientific and technical support in low-carbon crop production, for modifying China’s food system