Profile distribution of soil organic and inorganic carbon following revegetation on the Loess Plateau, China.

In arid and semiarid areas, which are characterized by fragile ecological systems, deforestation and tillage have resulted in a net loss of soil carbon to the atmosphere. Vegetation restoration has great potential to alter the soil carbon stock. Exploring sustainable vegetation restoration for carbon sequestration in soils requires adequate information on soil carbon and soil water. The vertical distribution of soil organic/inorganic carbon (SOC/SIC) and soil water in the 0-200 cm soil depth under cropland, forestland, shrubland, and grassland with restoration age (0-30 years) in Zhifanggou watershed on the Chinese Loess Plateau were investigated. The results showed that after 10 years vegetation restoration, SOC content at topsoil in forestland, shrubland, and grassland increased significantly, and SIC content at subsoil in shrubland and grassland increased significantly due to more pedogenic carbonate formed by Ca2+ derived from the decomposed litter and biogenic CO2. The absolute values of the slopes of the linear regression patterns between SOC and SIC were in the order grassland > forestland and shrubland and indicate that under the grassland the increment in SIC is larger per unit decrement in SOC. After 20 years vegetation restoration, the soil water content under forestland and shrubland decreased to 4.74%-6.16 and 4.08%-5.21% which are close to the wilting coefficient (5%) for the sandy loam soil in Zhifanggou watershed, resulting in the obstacle to sustainable land use. The conversion from cropland to natural grassland kept the relatively high level of soil water and may be the sustainable vegetation restoration approach to increase soil carbon.