Spatial Distribution Of Soil Inorganic Carbon Density, Stock And Its Affecting Factors In The Loess Plateau

Loess plateau is located at arid and semi-arid area and the soil layers is deep.There is much calcium carbonate on loess plateau which has important contribution tocarbon cycle in China. In this study, based on the Second National Soil Survey andLoess Plateau1:500000soil map, we collected495soil profiles and2136samples inthe loess plateau area. We estimated the soil inorganic carbon storage (SICS), density(SICD) and analyzed the effects on land use at the depth of0^-20cm,20-50cm,50^-100cm. The spatial distribution pattern of soil inorganic carbon density in theLoess Plateau was analyzed. Combined with a typical watershed of Zhifanggouwatershed which in hilly region of loess Plateau,142soil profiles (0^-200cm) and1750samples were collected which was used by grid method (200m×200m). Based on fourland uses (farmland, grassland, shrubland, woodland) and three topographies(tableland, slopeland, gullyland), we analyzed the effects of topographies and landuses on spatial distribution of soil inorganic carbon and estimated soil inorganiccarbon storage, soil organic carbon storage, soil total carbon storage in the watershed.The results were as follows:1. The0^-20cm of depth soil inorganic carbon density was3.31kg m^-2,0-50cmof depth soil inorganic carbon density was8.41kg m^-2and0^-100cm of depth soilinorganic carbon density was17.04kg m^-2in the Loess plateau. Soil inorganic carbonstorage were2.39Pg,5.31Pg and10.20Pg for the depth ranges of0^-20cm,0-50cmand0^-100cm of depth, respectively. Stocks for0^-20cm and0-50cm of depthaccounted for23.46%and52.08%of total Soil inorganic carbon storage, respectively.Soil inorganic carbon density mainly ranged from1to35kg m^-2, with an average of17.04kg m^-2. In terms of spatial distribution, the SICD on the northwestern of LoessPlateau was high because it rained less, the calcium carbonate's leaching is difficult and the calcium carbonate will deposit in soil. On the contrary, inorganic carbondensity (SICD) of southeast soil was very low as it rained more and the calciumcarbonate is leaching easily.2. Under different land use types, the SICD were farmland>grassland>woodlandin all soil layers, excepted that it was grassland> farmland> woodland in20-50cmlayer. SICD of grassland in0^-20cm was significantly different from that of woodlandor farmland. However, the difference between farmland and woodland was notsignificant. There were significant differences in SICD in20-50cm and50^-100cmlayers between woodland and farmland, as well as between woodland and grassland,while there was no significant difference between farmland and grassland.3. It was important to accurately assess regional spatial distributioncharacteristics and the influencing factors of soil inorganic carbon and to study effectsof land use and topographies on spatial distribution of soil inorganic carbon. Theterrain had a significant influence on the spatial distribution of soil inorganic carbonon Zhifanggou small watershed, ranged as: table land (15.32g·kg^-1)>slope land(14.45g·kg^-1)>gully land (12.27g·kg^-1). Compared with slope land, soil inorganiccarbon contents in the gully land decreased by15%and table land increased by6%.The average soil inorganic carbon content of0^-200cm was14.47g·kg^-1and thevariation coefficient was13.85%in the whole watershed. The soil inorganic carbonspatial distribution patterns were caused by loss of soil and water and different soilmoisture. Land use had profound impacts on the distribution of soil inorganic carbon.Soil inorganic carbon in shrub land was significantly higher than those in wood land,grassland and farmland. Woodland and grassland was significantly higher than thosein farmland, but there was no significant difference between wood land and grassland,ranged as: shrub land (14.98g·kg^-1)>grassland (14.59g·kg^-1)>woodland (14.43g·kg^-1)>farmland (13.49g·kg^-1). Moreover, the soil inorganic carbon of leaching andposition process was influenced by human activities, and it changed the spatialdistribution of soil inorganic carbon content.4. In different ways of land use, in the light of soil organic carbon density from0^-20cm,0-50cm layers, woodland and farmland lied in an area with less soil organiccarbon. Shrub-land and grassland located in an area with relative high soil organiccarbon density. While, in0^-100cm layers, soil organic carbon density of shrub-landwere in the area with more SOC. Woodland-land, meadow and farmland were in thearea with less SOC. However, in0^-200cm layers, soil organic carbon density of shrub-land, woodland and grassland were in high density area, and farmland were inlow density area. In0^-20cm,0-50cm soil layer, SIC density of shrub-land, andfarmland were in a area with less SIC, and woodland and grass-land were in a areawith relative more SIC. In0^-100cm,0^-200cm of depth, SIC density of woodland,shrub-land were in the area with more SIC, which of farmland and grassland were inthe area with less SIC. At the same time, we could found that SIC density proportiongradually increase with the increase of the soil layer, which illustrate that vegetationroot influence SIC density to a certain extent. The soil organic carbon density of0^-20cm,0-50cm,0^-100cm and0^-200cm was1.20kg m^-2,2.20kg C m^-2,3.49kg m^-2and5.93kg m^-2, respectively, were more lower than the corresponding density of Chinaand Loess plateau. The soil organic carbon density of0^-20cm,0-50cm,0^-100cmand0^-200cm was3.42kg m^-2,9.02kg m^-2,18.02kg m^-2and35.03kg m^-2,respectively, were more higher than the corresponding density of China. Soilinorganic carbon stocks and soil organic carbon stocks of Zhifanggou watershed in0^-20cm of depth was respectively28.6×10⁶kg C and9.70×10⁶kg C. Total soil carbonstocks was38.3×10⁶kg C; soil inorganic carbon stocks and soil organic carbon stocksin0-50cm of depth was74.6×10⁶kg C and17.9×10⁶kg C, which accounted for80.6%and19.4%of Total soil carbon stocks (92.5×10⁶kg C) respectively. Soilinorganic carbon stocks and soil organic carbon stocks in0^-100cm of depth wasrespectively28.5×10⁶kg C and147.5×10⁶kg C, and Total soil carbon stocks was92.5×10⁶kg C; Total soil carbon stocks0^-200cm of depth was334×10⁶kg which was1.17times higher than soil inorganic carbon stocks (285.6×10⁶kg C) and6.9timeshigher than soil organic carbon stocks (48.4×10⁶kg C). Soil inorganic carbon stockshad greater influence on Total soil carbon stocks. In addition, Total soil carbon stocksin100^-200cm of depth accounted for47.3%of Total soil carbon stocks in0^-2m soilayer. Total soil carbon stocks in deep soil layer had great potential and wasindispensable.