Effects of abandonment on deep soil organic carbon in mountain Ziziphus jujuba Mill. forests of the loess area in northern Shaanxi

This paper explored the distribution characteristics and influence of abandonment on deep soil organic carbon (SOC) in the Qijiashan mountain Ziziphus jujuba Mill. (jujube) forests of the loess area of Yanchuan County in northern Shaanxi. Research on SOC in the 0-340 cm soil layer showed that:SOC content and organic carbon storage in the study area exhibited obvious surface accumulation. Significant differences in SOC storage were found for different years of abandonment (P < 0.05). Deep SOC storage reached 60% of the entire soil profile, and SOC content in the 0-20 cm soil layer was positively correlated with the increase in abandonment years. The highest organic carbon content (12.62 g/kg) was found after 20 years of abandonment, whereas the lowest organic carbon content (7.82 g/kg) was found after 1 year abandonment. Deep SOC (200-340 cm) decreased with the increase in years of abandonment, but the differences observed among the different abandonment years were not significant. Furthermore, SOC content was significantly correlated with soil bulk density in the first year of abandonment, with soil available potassium after 3-6 years of abandonment, and with soil available nitrogen and gravel content after 20 years of abandonment. Thus, these results indicate that years of abandonment has little effect on the distribution of SOC in deep soil, but research on organic carbon in deep soil cannot be ignored.