Objective The aim was to analyze the spatiotemporal evolution of cultivated land soil fertility in Yuanping County and identify the main influencing factors, in order to provide theoretical support for soil quality improvement and scientific fertilization.

Method Data on soil organic matter (SOM), total nitrogen (TN), available phosphorus (AP), and available potassium (AK) from 1980, 2008 and 2021 in Yuanping County were used. The comprehensive soil fertility index (SFI) was calculated using an improved Nemerow index method. GIS and geostatistical methods were employed to characterize the spatiotemporal evolution of soil fertility and to identify its main influencing factors. A random forest model was used to determine the dominant control factors for different years.

Result ① The comprehensive SFI index increased significantly from 0.76 in 1980 to 1.24 in 2021, indicating a substantial overall improvement in soil fertility. ② Over the 41-year period, SOM and TN increased markedly, rising by 5.67 g kg⁻¹ and 0.45 g kg⁻¹. AP increased from 6.54 mg kg⁻¹ to 13.8 mg kg⁻¹. AK showed an initial decrease followed by an increase, dropping from 120.13 mg kg⁻¹ in 1980 to 97.12 mg kg⁻¹ in 2008, and then recovering to the level in 1980. ③ From 1980 to 2008, SOM and TN increased significantly in all areas except for the eastern cultivated land. SOM in approximately 35% of the cultivated land increased from level V to level IV, and TN in about 42% of them promoted from level V to level IV. Approximately 53.9% of the cultivated land in the city improved its AP from level IV to level III, while 41% of them experienced a decrease in AK from level III to level IV. Between 2008 and 2021, about 9.2% of cultivated land showed an improvement in SOM from level IV to level III, and 9% of them showed an improvement in TN from level IV to level III, both primarily located in the central part of the county. AP levels showed no significant change during this period, but 48% of the cultivated land showed an increase in AK from level IV to level III. ④ In 1980, the dominant factors controlling soil fertility were AP and AK, with contribution rates of 32.1% and 30.6%. By 2021, the contribution rates of AP (27.9%), AK (24.3%), SOM (23.4%), and TN (24.4%) to soil fertility were similar.

Conclusion Over the past 41 years, the soil fertility of cultivated land in Yuanping County had significantly improved, with 86.2% of the cultivated land improving from level IV to level III. The overall spatial distribution of soil fertility showed a "low in the east and west, high in the central region" pattern. In some parts of Xinyuan, Zhongyang, and Yangou townships in the central region, the content of TN, AP and AK had decreased compared to 1980, primarily due to changing in planting structure and fertilization ratios. Therefore, the future fertilization strategies should be tailored to the planting structure changing in each township to balance soil nutrients and further improving soil fertility.