Characteristics And Driving Factors Of Carbon Saturation Deficit In Typical Cropland In China

Soil organic carbon(SOC)is the core of soil fertility,and is closely related to the global carbon cycle.Stable SOC pool(C associated with mineral particles,MOC)is an important part of SOC,and become a hot area of research in modern soil science.The concept SOC saturation suggests that the quantity of stable SOC is limited and determined by the amount of mineral particles(clay + silt)and soil mineralogy.The difference between the theoretical SOC saturation value and the measured MOC corresponds to the soil's C saturation deficit(CSD)and may represent the potential for SOC sequestration in a stable form.CSD is presumed to affect the capacity and rate of SOC storage.Total soil organic carbon(TOC)is low in Chinese cropland,however,the temporal and spatial variation of C saturation deficit of mineral parcicles is unkown,and how the soil,climate and management practices interaction affect the CSD is unclear.Several typical long-term fertilization experiments in China were selected,to analyze the CSD temporal variation of soils in three field scale sites and the CSD spatial variation of soils in multiple sites and to assesses the main significantly effect factors among climate,soil properties and management practies and to quantify the contributions to CSD value.Moreover,this study tested wethere C saturation ocured in TOC and MOC.The major results and conclusions were as follows:(1)CSD under manured treatments was decreased significantly with fertilization times,and the change rate of CSD under manured treatments were followed as Gongzhuling>Qiyang>Urumqi.Dynamics of CSD was controlled by the combination of soil nutrient,the amount of C inputs and temperature,and they could explain 86.4%variation of CSD in all three sites.The main driving factors that affected CSD were different among the three indivial site,and soil nutrient or C input amounts was the major factor regulating CSD at indivial site.(2)MOC content and the proportion of OC stored in the fraction<20 ?m related to the TOC content were higher of soils in north region than that of soils in south region.Among the variables,we found that mean annual precipitation(MAP)was the main driving factor influencing MOC content,and explained 20.9%of the variation of MOC content.The pH value was the most influential variables on MOC/TOC spatial variation and explained 33.5%of the variation of MOC/TOC.The results also showed that soil properties were the mainly factors the affected MOC content and MOC/TOC,and soil properties explained 29.4%and 66.6%,respectively,of the variation of MOC content and MOC/TOC.Precipitation and pH were the key factors to regulate MOC content and MOC/TOC at region scales.(3)Cropland soils in China had large CSD with average 68.6%(absolute potential was with average 31.1 Mg/ha)even after 20 to 35 years of fertilizer application,suggesting that soils in northern China can sequester a higher amount of C inputs.CSD was greater in soils dominated by 2:1 clay minerals than in soils dominated by 1:1 clay minerals.Climate factor was the most influential variables on CSD and 29.2%and 63.1%of the variance for relative CSD and absolute CSD could be explained by climate factor,respectively.Individual environmental factor,the MAP and C inputs were the mainly control factors on relative CSD,explained 27.8%and 8.3%variations of relative CSD,respectively.The main individual control factors for the absolute CSD were MAP,elevation and mean annual evaporation,explained 44.6%,10.4%and 8.2%variations of absolute CSD,respectively.(4)There was no obvious relationship between soil carbon sequestration effencicy(CSE)and CSD for TOC and MOC,indicated that there was no C saturation occurred in TOC and MOC,and the soils could sequestrated the additional C at a steady rate.The CSE for TOC and MOC were 7%and 2%,respectively.