Objective The aim was to explore the characteristics of soil nutrients in terraced fields with different ages, and to understand the change of soil fertility. The results would provide a scientific evidence for the soil quality of terraced fields.

Method Terraces, constructed at different times (2010、2014、2018、2022) in Yonghe County, middle reaches of the Yellow River, were selected as the research objects. The modified Nemero Comprehensive Index method and correlation coefficient method was employed based on the nutrient classification standard from the Second National Soil Survey to comprehensively evaluate soil fertility levels in terraced fields with different ages.

Result The terraced soil in Yonghe County was weakly alkaline and relatively compact. The soil nutrient levels of total nitrogen, organic matter, total phosphorus, available phosphorus, and available potassium were all below the moderate level, showing the contents in level four or level five. The soil total potassium level was high, belonging to the upper middle level (contents were in level three). With the increasing of constructed ages of terrace fields, the nutrient contents of the surface soil gradually increased, while there were differences in other soil layers (no obvious pattern). The average values of soil fertility index (SFI) obtained by using the modified Nemero Index method and correlation coefficient method were 1.00 and 1.04, showing the fertility level was level three. With the increasing of constructed ages of terraced fields, SFI showed a trend of first decreasing and then increasing.

Conclusion The soil fertility level of terraced fields in Yonghe County in the middle reaches of the Yellow River was average. With the increasing of constructed ages of terraced fields, the soil nutrient contents gradually increased and the soil fertility level improved as well. However, scientific fertilization and management should still be carried out to improve the contents of soil organic matter, nitrogen and phosphorus.