Objectives This study aims to the spatio-temporal evolution characteristics of soil fertility indicators and the variation of soil fertility grades in Changyang Tujia Autonomous County, Hubei province, thereby providing a scientific basis for sustainable agricultural development in the region.

Methods We collected soil pH, organic matter (SOM), total nitrogen (TN), available phosphorus (AP), and available potassium (AK) data from Changyang County during 2007−2015, 2018, and 2022. The weights of each indicator were determined using the correlation coefficient method. Membership function curves were chosen and the turning points of the membership functions were identified. The fuzzy mathematics (Fuzzy) comprehensive evaluation method was employed to calculate the integrated fertility index (IFI) based on the weight values and membership values of each soil fertility indicator. The spatio-temporal evolution characteristics of each soil fertility indicator and IFI were analyzed using geostatistics and geographic information system (GIS) technologies.

Results From 2007 to 2022, spanning a 15-year period, the average values of soil pH, organic matter (SOM), total nitrogen (TN), available phosphorus (AP), and available potassium (AK) increased by 0.47 units, 1.24 g/kg, 0.57 g/kg, 38.67 mg/kg, and 119.44 mg/kg, respectively, all showing moderate variability. From 2018 to 2022, the proportion of neutral pH soil area in Changyang County increased by 29.41 percentage points, soil area with Grade Ⅱ SOM content increased by 14.04 percentage points, soil area with TN content of Grade Ⅱ or above decreased by 17.92 percentage points, and soil area with Grade I AP content and Grade Ⅱ AK content increased by 81.13 percentage points and 42.45 percentage points, respectively. The nugget coefficients for pH and TN fell within the 25% to 75% range, indicating moderate spatial correlation, whereas those for SOM, AP, and AK were below 25%, suggesting strong spatial correlation. In 89% of Changyang County’s farmland, IFI reached Grade Ⅲ or higher, with the area of farmland having IFI≥Grade Ⅱ increasing by 7.87 percentage points from 2018 to 2022. SOM and TN were identified as the primary factors contributing to variations in soil fertility. The spatial distribution patterns of IFI were comparable to those of SOM and TN, with farmland having IFI≥Grade Ⅱ predominantly concentrated in the northern, western, and central regions, while the eastern and southern regions displayed medium to lower soil fertility levels.

Conclusions Over the 15-year period, the farmlands in Changyang County have transitioned from acidic to neutral, with SOM, AP, AK, and soil fertility levels consistently increasing. The soil fertility index in 52% of the farmlands has reached relatively high levels. However, the distribution of high-fertility farmlands across the county is uneven. SOM and TN are the key factors driving the improvement in the IFI. Therefore, considerable attention should be given to applying organic amendments to enhance SOM levels, thereby promoting high nitrogen sequestration and fertility potential.