民勤绿洲区撂荒农耕地土壤有机碳变化特征及影响因素

对民勤绿洲区不同撂荒年限农耕地0-60cm土体4个土层中土壤总有机碳（TOC）、轻组有机碳（LFC）和重组有机碳(HFC)剖面分布以及与土壤主要属性的关系进行比较研究。结果表明:(1)撂荒区0-60cm土层土壤，TOC、LFC和HFC含量分别介于3.21-5.23g/kg、0.34-1.51 g/kg、2.55-4.30 g/kg之间，相对于常规耕作,撂荒过程中土壤TOC 、LFC和 HFC的下降主要发生在耕层（0-20cm），撂荒50年间，TOC 、LFC和 HFC年均减幅分别为1.94%,5.46%和2.13%；20-60 cm土层土壤TOC和HFC含量总体呈现缓慢增长的趋势，撂荒50年TOC和HFC年增幅分别为0.31%和0.88%，LFC持续减少，年均减幅为1.18%。(2)撂荒地HFC对TOC的贡献大于LFC,土壤TOC和HFC分别与粘粒百分比（Clay）和粉粒百分比（Silt）呈极显著正相关，与沙粒百分比（Sand）呈极显著负相关，LFC与Silt、Sand和Clay均未达到统计学上的显著水平，但LFC分别与土壤pH、EC和SAR达到显著或极显著水平，说明LFC对土壤盐碱化较为敏感。(3)逐步回归分析表明，土壤全氮（TN），总碳氮比（TOC/TN）对土壤TOC 、LFC和 HFC影响较大。（4）随撂荒时间延长，耕层土壤逐步趋于粗质化，粘粉粒含量不足，容重降低，盐碱化提高，不利于土壤有机碳的积累，随土层加深，粘粉粒含量提高，有助于土壤有机碳的固持。

Changes and Influencing Factors of Soil Organic Carbon in Abandoned Cropland of Minqin Oasis Region

This study is aimed to investigate the dynamics of total soil organic carbon(TOC), light fraction organic carbon (LFC) and heavy fraction organic carbon (HFC) concentration, its profile distribution and influence factor in an anthropogenic-alluvial soil at Minqin Oasis Area under six abandonment time series. In each Sampling area at 0-60 cm depth, soil samples were collected from four layers. The results showed that,(1) TOC, LFC and HFC content were between 3.21-5.23g/kg, 0.34-1.51 g/kg and 2.55-4.30 g /kg respectively in this soil profile,TOC,LFC and HFC decline mainly occurred in the tillage layer (0-20cm) after 50 years abandonment, compared to conventional tillage, the annual decline rate of TOC, LFC and HFC were 1.94%,5.46% and 2.13%. In general,TOC and HFC content in 20-60 cm soil depth showed a slow growth trend, compared with cropland under conventional tillage,the annual increase rate of TOC and HFC were 0.31% and 0.88%, but LFC continued to decline,with an annual decrease of 1.18%.(2)HFC contribution of to TOC is greater than LFC on abandoned land,the soil TOC and HFC were highly positive significant correlation with clay percentage (Clay) and silt percentage (Silt) respectively,and negatively significantly correlated was sand percentage (Sand) ,LFC is not reach significant level in statistics with Silt, Sand and Clay, but LFC had significant or highly significant relationship with pH, EC and SAR, indicating LFC was more sensitive to soil salinization.(3) Stepwise regression analysis showed that soil total N (TN), total nitrogen ratio (TOC / TN) had greater impact on soil TOC,LFC and HFC.(4)With long time abandonment, tillage layer became rough,clay and silt lacked,bulk density decreased,salinity increased,and did not favor accumulation of soil organic carbon, with soil horizon deepen,clay and silt increased ,it benefit for soil organic carbon accumulation.