Carbon Sequestration Benefit and Influencing Factors in Terraces with Different Cover Types of Soil in the Loess Hilly Region

Abstract: Terraces and vegetative measures significantly enhance soil organic carbon levels and improve the efficiency of soil carbon sequestration, serving as crucial soil and water conservation strategies. There are few studies on the differences and influencing factors of soil organic carbon sequestration benefits resulting from the combination of engineering measures and plant measures. Thus, the study analyzed the variations in soil organic carbon content(SOC) and its primary influencing factors across different vegetation cover types in terraces, and evaluated the soil carbon sequestration benefits of terraces. The study selected 96 sample plots in Wuqi County, Shaanxi province, including 37 Terraced Croplands (TC), 23 Terraced Grasslands (TG), 18 Terraced Forestlands (TF), 10 Terraced orchards (OL), as well as 8 Slope Croplands (SC) on hillsides. Soil samples were collected from soil layers at depths of 0-10 cm, 10-20 cm, 20-40 cm, 40-60 cm, 60-80 cm, and 80-100 cm, totaling 576 soil samples. In the laboratory, we measured indicators such as soil organic carbon, soil moisture content, soil bulk density, and soil mechanical composition. 1) The SOC in the 0-100 cm soil layer of the four types of land cover under the terrace ranged from 2.34 to 3.42 g/kg, with the order of TF> OL> TG> TC. 2) After SC is convert into TF, TG, TO and TC, it has improved the carbon sequestration benefits of soil. The carbon sequestration of TF, TO, TG and TC is 12.01, 8.78, 8.13 and 2.13 t/hm², respectively. 3) The vertical distribution of soil carbon sequestration benefits differs among various land cover types. The soil carbon sequestration benefit of terraced fields is higher in the 60-100 cm soil layer than the 0-40 cm soil layer. However, when terracing is combined with vegetation measures, the trend is reversed. 4) The SOC of TF, TG, TO TC, and SC exhibits a significant negative correlation with soil bulk density and an extremely significant positive correlation with soil moisture content, respectively. However, compared to SC, only the soil moisture content of TC and TO shows a significant increase. The implementation of terrace measures influences soil carbon sequestration benefits by increasing soil moisture, especially enhancing the sequestration in deep soil layers. When terraces are combined with vegetation measures, the soil carbon sequestration benefits are further enhanced, with a particularly greater impact on the sequestration benefits of surface soil. The results of our study could provide strong support for achieving the effects of relevant soil and water conservation measures and developing carbon sequestration methodology.

Keywords: soil and water conservation; soil carbon sequestration; terrace; Loess Plateau; monitoring and evaluation