The tempo-spatial changes of soil fertility in farmland of China from the 1980s to the 2010s

The grain yield level is closely related to soil fertility. To clarify the status and variations of soil fertility in Chinese farmland, soil sample profile data from the Soil Species of China in the 1980s and the Soil Series of China in the 2010s were collected. And surface soil data of fertility indexes (pH, soil organic matter, total nitrogen, total phosphorus, and total potassium) were calculated. The tempo-spatial variations characteristics of both soil fertility indexes and soil comprehensive fertility of Chinese farmland were analyzed with descriptive statistics, comparative analysis of paired sample points, and Integrated Fertility Index method. The results showed that: 1) The farmland soils in southern China were acidic and those in northern were alkaline. From the 1980s to the 2010s, the pH mean decreased by 0.34, and the acidification of soils in the southern region was more significant; 2) SOM and TN contents showed similar spatial patterns, with higher contents in southern and northeastern regions. Compared with the 1980s, the SOM mean and TN mean in the 2010s increased by 2.72 g/kg and 0.06 g/kg, respectively, with a decreasing trend in some areas; 3) The spatial distribution of TP and TK contents showed significant variability, with change range of the mean values was 0.15 g/kg and −1.51 g/kg during the three decades, respectively; 4) In general, the soil fertility in Chinese farmland was poor, with the most sample points at Grade IV (Mid-low) in the 2010s (22.38 %). During the three decades, the IFI mean increased by 0.01. The number of sample points with increasing IFI in eastern China was more than that in western China. And the soil fertility in eastern China showed a trend of ameliorating. This study would have great scientific significance for guiding agricultural fertilizer application and improving fertility in farmland soils.