Objective The “carbon neutrality” strategy puts forward higher precision requirements for the estimation of regional soil carbon stocks and the magnitude of carbon source or sink. The present calculation method is based on the classical statistical theory with the hypothesis of random sampling, and the spatial autocorrelation of the data is not considered. As a result, the accuracy of calculation is limited. Therefore, it is necessary to develop a more scientific and reasonable method.

Methods Taking the multi−purpose regional geochemical survey (MPRGS) and 1∶50000 land quality geochemical survey (LQGS) data in Shandong province as an example, a new method for soil carbon source or sink estimation was developed through theoretical calculation and formula derivation based on the theory of geostatitics.

Results Key points of the new method include: ① the spatial distribution of carbon density and its prediction error is obtained based on the punctual−kriging method; ② the block−kriging method is used to obtain the regional carbon storage with its error; ③ the method calculating the spatial change of the carbon density with its error is given; ④ the method of zoning the carbon source and sink areas is given; ⑤ the formula for calculating the amount of storage change with its error range is given. The case study showed that the 0−20 cm organic carbon storage of the cultivated land in Shandong province is 141.15±0.30 Tg. In recent decades (2003—2020), the soil of drylands, irrigated lands, and paddy fields in representative areas totally acted as carbon sinks.

Conclusions The new method based on the geostatistical theory does not require random sampling, and the effect of spatial autocorrelation is fully considered. It can be used to define the boundary of areas for carbon source or sink and deduce it total amount effectively. This study provides a scientific and feasible method for soil carbon accounting.