Agricultural activities are one of the main causes of global warming due to the emissions of greenhouse gases such as carbon dioxide, and the key to effectively solving this problem is to reduce carbon emissions and increase carbon sequestration 1.2.3. On the one hand, the total carbon emissions generated by agriculture are very large, accounting for approximately 25% of the total global carbon emissions4, and there is a long way to go to reduce carbon emissions. On the other hand, agricultural production activities, such as farmland and forests, can effectively absorb carbon dioxide and other greenhouse gases through their own carbon sequestration capacity, i.e., agriculture has a significant carbon sink capacity5.6.7.
Traditional farmland has problems, such as fragmented cultivation and incomplete infrastructure during cultivation and reclamation, resulting in the emissions of a large amount of carbon dioxide and other greenhouse gases, which cause different degrees of damage to agricultural production and life and the natural ecological environment, thus affecting the improvement of farmland quality and agricultural carbon emission reduction. The construction of high-standard basic farmland can effectively achieve a significant reduction in farmland carbon emissions and a stable increase in farmland carbon sequestration capacity through the implementation of land levelling projects, irrigation and drainage projects, field road projects, farmland protection projects and typical field remediation methods8. These practices could promote the further development of agricultural emission reduction and carbon sequestration. On May 7, 2022, the Ministry of Agriculture and Rural Affairs and National Development and Reform Commission passed the "Agricultural Rural Carbon Emission Reduction Program" and proposed that among the six key tasks and ten major actions for agricultural emission reduction, the construction of high-standard basic farmland is an effective way to expand the carbon sequestration capacity of farmland, accelerate arable land governance and quickly compensate for the shortcomings of agricultural infrastructure.
Whole life cycle theory (WLCT) refers to a design concept that considers the entire construction cycle of a project at the initial design stage and plans all relevant factors in each stage of the construction cycle 9.10.11.12. Currently, it is mostly used in various construction projects, i.e., the whole life cycle of engineering and construction projects, including the five stages of decision-making, design, construction, operation, and end-of-life recycling. The research results show that the carbon emissions generated by construction projects based on the whole life cycle theory are reduced, which is in line with the concept of green building development. This paper intends to study the carbon emissions and carbon absorption (hereinafter referred to as the carbon effect) generated by high-standard basic farmland construction projects in the process of farmland improvement based on the whole life cycle; additionally, this study evaluates and analyses the carbon effect of the whole life cycle of farmland construction, using three high-standard basic farmland construction projects of different scales in Tianjin, China, as examples13.
The whole life cycle of the high-standard basic farmland construction process includes the decision design stage, construction stage and operation management stage from the beginning to the end of high-standard basic farmland construction 14. The carbon effect is mainly reflected in the construction stage and operation management stage. Because the actual change in the carbon effect is not involved in the initial decision and design stage of the construction of high-standard basic farmland, this paper does not measure or analyse it. The carbon effect in the construction stage refers to the carbon emissions generated by the consumption of materials, the use of appliances and the input of personnel during the construction of high-standard basic farmland. The carbon emissions and carbon absorption generated by the conversion of land-use types before and after the construction of the project are also part of the carbon effect in the construction stage15. The carbon effect in the operation and management stage refers to the change in the carbon effect in the field ecosystem due to the increase in effective arable land area and the improvement in land quality after the construction of high-standard basic farmland16.