Spatiotemporal evolution and distribution of net carbon sink under conservation tillage in Shaanxi Province, China

Conservation tillage is one sustainable practice in green farming recommended by the Food and Agriculture Organization of the United Nations. Long-term conservation tillage can contribute to farmland, water and moisture preservation. At the same time, the ecological environment can be effectively improved for the high crop yields. Furthermore, conservation tillage can also be benefitical to the outstanding carbon sequestration and emission reduction, thus mitigating global warming. Taking Shaanxi Province as the research area, this study aims to explore the spatiotemporal evolution and region distribution of net carbon sink under conservation tillage. Shaanxi Province is a typical dry farming area in northwestern China. Diverse landforms are also distributed in the long and narrow from the north to the south, covering the plateau, plain and mountainous. There are many agricultural types, such as dry farming and paddy fields, one or multiple cropping, plain or mountain agriculture. Conservation tillage was introduced to the project construction in 1999. Firstly, the net carbon sink of conservation tillage was quantitatively measured in each city from 2000 to 2020. Then, the Kernel density function and the trend surface analysis were implemented to obtain the evolution of the land patterns from the time and space dimensions. Finally, the Dagum Gini coefficient was selected to represent the variability in the net carbon sink of conservation tillage. Furthermore, the contribution rate was determined to clarify the source of differences. The results showed that: 1) The net carbon sink of conservation tillage showed the trend of "stable-rising-fluctuating rising". There was a significant increase from 57.76×10⁴ t in 2000 to 129.30×10⁴ t in 2020, with an increase of 123.86%. Both net carbon sink and intensity of conservation tillage showed a spatial distribution pattern of "high in the center and low in the north and south". There was the largest increase (24.27×10⁴ t) in the net carbon sink of Weinan at the city level, followed by Yulin and Yan’an. Xi'an was ranked the last. 2) In the time dimension, the Kernel density curve of net carbon sink under conservation tillage was characterized by a "rightward shift of the main peak and a gradual widening of the wave crest" with a "rightward trailing" evolution. In terms of spatial dimension, the trend surface was relatively flat in the east-west direction, while the upward trend surface in the north and south presented an inverted U-shaped distribution of "high in the center and low in the north and south", indicating the more outstanding differentiation. 3) There was an ever-narrowing variation in the overall net carbon sink of conservation tillage. The contribution rate of inter-regional differences was 67.22%, which was the main source from the spatial non-equilibrium of the overall net carbon sink under conservation tillage. The finding can provide the theoretical basis to promote the core and key areas of conservation tillage. At the same time, the decision-making reference can be expected to determine the key promotion areas of conservation tillage, in order to optimize the promotion policy and agricultural contribution to the national "dual carbon" goals.