Spatiotemporal characteristics of cultivated soil fertility in the intensive agricultural region of North China: A case study of Quzhou County in Hebei Province

Fertility is a fundamental characteristic of soil, reflecting its ability to provide nutrients and an environment essential for plant growth. It is a comprehensive reflection of soil's physical, chemical, and biological properties. Scientifically and accurately evaluating the soil fertility in cultivated land and revealing the spatiotemporal characteristics of soil fertility are of great significance for guiding agricultural production and sustainable use of cultivated land resources. The present study focused on Quzhou County, a typical county in the region of intensive agriculture in North China. Based on the test data of soil sample points of cultivated land and data of cultivated land utilization, fuzzy comprehensive evaluation and geostatistical methods were used to evaluate the soil fertility of cultivated land to reveal the spatiotemporal evolution of cultivated land soil fertility. The results showed that soil organic matter, total nitrogen, available phosphorus, and available potassium of the cultivated land increased, whereas pH decreased, from 2000 to 2018, which were all affected by both structural and stochastic factors. The mean soil fertility index of cultivated land increased from 0.25 to 0.54 from 2000 to 2018, and the growth rate was 116.00%. The soil fertility of cultivated land changed from a lower level to a medium level, and the overall degrees of variation and spatial autocorrelation were at medium levels. The levels of soil fertility of cultivated land in 2000 and 2018 were mainly grades Ⅱ and Ⅲ, accounting for 83.92% and 50.43%, respectively, these lands were widely distributed in all towns except for Houcun and Yizhuang. The levels of cultivated land soil fertility of grades Ⅰ and Ⅱ decreased, whereas those of grades Ⅲ, Ⅳ, and Ⅴ increased from 2000 to 2018, and the Ⅱ degree transferred area and slightly increased area were the largest. The area of conversion from grade Ⅱ to grade Ⅲ was the largest, accounting for 59.49% of the total area, and the tendency for a slight increase in soil fertility of cultivated land was most common, accounting for 52.59% of the total area. However, the cultivated land areas of highest grade and with the highest increase were relatively small, constituting only 1.86% and 3.34%, respectively, of the total area. The results showed that, with the exception of pH, the nutrient features of cultivated soil increased in Quzhou County from 2000 to 2018, and the quality of cultivated land soil fertility changed from low to medium, which was affected by the natural background and manmade agricultural production activities. Therefore, the effective balance and coordination of soil nutrient content are helpful to improve soil fertility and sustainable use of land resources.