|Other Abstract||Oasisization,as a unique ecological evolution mechanism of arid and semiarid regions, is a transition process that changes from desert to oasis,which is caused by human activities and natural factors together.The irrigation area in Northern Tarim Basin,as a typical oasis agriculture area,of which the soil physical and chemical properties and organic carbon content changes along with the process of oasisization,affecting the changes of cropland soil organic carbon pool.Based on analyzing the typical sampling sites of the irrigation area in Northern Tarim Basin in different periods and combined with the data from the second national soil survey and agricultural information of this area, the storage and density fluctuation of soil organic carbon were analyzed by Arc GIS, revealing the evolvement rules of cropland soil organic pools, analyzing the relevantly impacting factors of soil carbon sequestration and estimating the carbon sequestration potential of the irrigation area in Northern Tarim Basin and South Xinjiang. The research is aimed at providing scientific guidance to improve the soil quality and increase crop yields of this area. Moreover, it can provide theoretical support for carbon estimate of Xinjiang as well as Northwest Territories in China, serving for national climate negotiations. The results are as follows:
（1）The soil organic carbon content of different soil types were of great significance
The capacities of cropland carbon sequestration for different soil types were of great difference,and from high to low, the organic carbon content were meadow soil, solonchak soil, fluvo-aquic soil and aeolian sandy soil, respectively, and the content of organic carbon for aeolian sandy soil was far less than the average content of the region. On the scale of soil profile, the content of organic carbon were decreased from epipedon to bottom,which was closed related with long-term cultivation and cropland management . The space distribution of soil organic carbon density in the irrigation area in Northern Tarim Basin was of significant difference, showing a distribution pattern which decreased from the southwest to the northeast generally. The soil organic carbon density change laws were in
line with soil organic carbon content. The soil organic carbon density of different soil genus in one soil type was not significantly different.The total organic carbon pool of the irrigation area in Northern Tarim Basin was about 87.64 * 107 kg. The capacities of carbon storage in different types were of great difference, which decreased from shrubby meadow soil, meadow soil, saline soil to aeolian sandy soil in turn; meadow soil carbon pool, whose carbon storage was about 46.31*107 kg, occupying the proportion as high as 52.85%, was the largest carbon pool in this area.
（2）Soil organic carbon content increased in 30 years (1981-2011)
Soil organic carbon content and density of the irrigation area in Northern Tarim Basin increased from 1981 to 2011. Soil organic carbon density in southwest, south central and southeast area increased with the increment of 0.9503 kg·m-2, while the north central and northeast showed negative growth at the same time. The carbon storage increased with the average rate of 0.01 kg·hm-2·a-1 slowly, and topsoil carbon sequestration increased area rated 61 %, decreased area rated 25%, with the relative balance of the area accounted for 14%.
（3）The change of soil organic carbon content was the result of many impacting factors
The main impacting factors that affected the agricultural organic carbon sequestration included three aspects: cropland reclamation duration, cropland management measures and soil physical and chemical properties.Reclamation duration had a significant impact on soil organic carbon accumulation. Compared with newly-reclaimed land, the soil organic carbon of croplands which were reclaimed for more than 30 years was significantly higher than those whose reclamation duration were less than 30 years. A regression equation of soil organic carbon(y) and reclamation duration(x) was obtained (y = 0.002x2 + 0.0737x + 1.9883, R² = 0.9014).Cropland management measures were important impacting factors of soil organic carbon sequestration of the irrigation area in Northern Tarim Basin. The high proportion of straw mulching of different crop types,combined organic manure and chemical fertilizers application, and the adequate irrigation water, were improving the content of soil organic carbon effectively.Soil organic content had significant positive correlations with soil bulk density, percentage of clay and particle, but negative correlations with percentage of sand. The content of SOC had significant positive correlations with total N, P, K and soil available P, and had no significant correlations with pH and soil available K. In general, the correlation coefficients of SOC and soil nutrients were in a decreasing order of TN >TP>AP>TK>AK. An optimal stepwise regression equation of soil organic carbon(y) and TN (x1),TP (x2),AP (x3) and TK (x5) was obtained （y=5.464x１+31.603x2+0.1771x3+23.552x5-3.184，R2=0. 653，P<0.001）
（4）The soil carbon sequestration potential was great
The carbon sequestration potential of cropland soil organic carbon for different soil types were of great difference in the irrigation area in Northern Tarim Basin. The carbon sequestration potential of solonchak soil was 1.69 kg·m-2, which was much higher than other four soil types. Therefore, more management of salinization and amendment of solonchak soil would greatly improve the carbon sequestration potential of the irrigation area in Northern Tarim Basin. The total carbon sequestration potential of the irrigation area in Northern Tarim Basin was large, with the capacity of 59.32*107 kg.In general, the carbon sequestration potential of south Xinjiang was huge, with the capacity of 22.96*109 kg. The top 3 soil types of the carbon sequestration potential were solonchak soil, deserty solonchak soil and luvo-aquic soil, with the values 1.64 kg·m-2, 1.06 kg·m-2 and 0.98 kg·m-2, respectively. The carbon sequestration potential of calcic brown soil was less than0.05 kg·m-2, and the carbon sequestration potential of the remaining soil types were between 0.5~1.0 kg·m-2.|