Effects of age and land-use changes on soil carbon and nitrogen sequestrations following cropland abandonment on the Loess Plateau, China

Vegetation restoration and revegetation on land abandonment of cropland has a major impact on the landscape of the Loess Plateau in China. Such processes can alter soil carbon (C) and nitrogen (N) pools and cycling. However, few studies have examined the effect of cropland abandonment on soil C and N sequestration in various land-use types over time. We studied the effects of age and land-use change types on soil C and N sequestration in top 1-m soil depth in the transition from forest to grassland in the center of the Loess Plateau. The results show that age as well as land-use change types had a significant effect on soil C and N sequestrations. Soil C and N sequestrations in the surface soils (0–10 cm) had always increased since cropland abandonment. In the first 10 years, the orchard (OL) and man-made grassland (alfalfa) had higher soil C and N sequestrations than the other types of land uses, such as natural grassland (NG), shrubland (SL), orchard (OL) and woodland (WL). Moreover, in the later stage since cropland abandonment (>20 years), the SL had the high soil C and N sequestrations followed by WL and NG. In addition, the correlations between soil C and N sequestrations were greater in surface soil layers than that in deeper layers, and soil C sequestration was approximately 8–10 times that of soil N sequestration after cropland abandonment. Our study suggests that to get long-term (>20 years) soil C and N sequestration benefits, planting shrubs is a better restoration type in the transition from forest to grassland than natural grassland and woodland on the Loess Plateau, and orchard and man-made grassland (alfalfa) influenced by fertilization also have a good soil C and N sequestration benefits in the short time (<20 years) .