Spatial distribution of organic carbon in coastal saline soil and its correlation with reclamation age

With the impact of global climate change, the concern with ecosystem carbon sources and sinks has been growing. Soil carbon pool is the largest terrestrial ecosystem and the turnaround time is the slowest, which is the important factors controlling the size of the CO2 concentration in the atmosphere. Coastal saline soils is a kind of neoformative soils which has poor soil physical and chemical properties and low level fertility. There are approximately 2,000 hectares in China, which means a large potential soil carbon pool. In this study, the surface soil organic carbon content (SOC) was analyzed through soil samplings within the Dongtai county, which is located in the middle and lower reaches of the Yangtze River Plain, with beach area of 156 hm2. There are different seawalls of ages from ancient times. With the geographic information system (GIS) method and SPSS 16.0 system, the spatial variations of surface SOC were investigated, which turned out a strong relationship with the seawall inning line, the lowest near the sea, and increasing from the beach to the inland. The correlations of the surface SOC, total nitrogen content (TN), pH value, EC1: 5 values under different beach reclamation ages were analyzed. The results showed that there was a significant positive correlation (P＜0.01) between SOC and TN, reclamation ages, and the correlation coefficients (r) are 0.959 and 0.749, respectively. Meanwhile, a significant negative correlation (P＜0.01) was presented between SOC and EC1:5, pH value, the correlation coefficients were -0.478 and -0.649, respectively. High EC1:5 and pH value were significant features of coastal saline soils, which limited the growth and reproduction of soil microorganism, fauna and flora, as well as the accumulation of organic matters. With more than 3 years of reclamation, under natural vegetation succession or human agricultural use, especially after irrigation and other agricultural production activity, the soil salinity reduced greatly, and the surface SOC and TN can increased about 0.24% and 0.02% respectively, comparing with the values before reclamation. After 52 years reclamation, the surface SOC increased from 0.1% to 1.6%, the TN increased from 0.03% to 0.12%. While the nutrient level increased from six class to three class accordingly. This study indicated that the EC1:5 and pH value decreased with the increasing reclamation period, and soil carbon storage and total nitrogen content increased with the increasing reclamation period. Therefore, the quality of coastal saline soils was improved through reclamation process.