The Influence of Terraced Field Construction on the Physicochemical and Microbial Properties of Ground Substrate in Northern Shaanxi Loess Hilly Areas

The Loess Hilly Region of northern Shaanxi is one of the most erosion-prone areas in the world due to its porous, erodible loess, steep slopes, and seasonal rainfall. To address this, conversion of sloping farmland to terraces has been extensively conducted across China’s loess regions, as terracing can reduce soil and water loss and enhance soil fertility. However, disturbance of soil layers during terracing can also lead to short-term decline in farmland productivity. This study investigates the effects of terracing operations at two sites of different ground substrate configurations in the Loess Hilly Region. Utilizing geochemical and molecular biological analysis methods, we examined the changes in the physicochemical and microbial properties of the ground substrate after terracing, using adjacent sloping farmlands as control sites. The results show that when the ground substrate configuration remained intact, terracing increased the average water content (from 8.44% to 14.34%) and soil organic carbon (from 2.74 g/kg to 5.76 g/kg) by 70% and 110%, respectively, and increased soil microbial α-diversity by 90%. The microbial community structure was also enhanced with an increase in relative abundance of soil- and plant-benefiting genera such as Streptomyces and Nocardioides, thereby promoting plant growth. Conversely, when the ground substrate configuration was altered, terracing led to a decrease in soil nutrient and moisture content, which was detrimental to crop growth. Therefore, maintaining the integrity of the ground substrate configuration is crucial during the terracing process to achieve optimal soil and water conservation outcomes.