民勤绿洲区苜蓿地土壤有机碳组分分布特征

为了解西北民勤绿洲区紫花苜蓿种植后土壤有机碳组分的变化趋势及影响因素,以民勤绿洲区3a(A3)、14a(A14)和22a(A22)苜蓿种植地为研究对象,以棉花种植地(CK)为对照,通过野外调查取样以及室内测试分析,对土壤中的全部有机碳(TOC)、重组有机碳(HFOC)、轻组有机碳(LFOC)、颗粒有机碳(POC)和微生物量碳(MBC)的含量进行测定,分析变化趋势并对其规律进行研究。结果表明:相对于棉花种植地,22a苜蓿地土壤容重和电导率分别降低了13.9%和95.4%。3~22a苜蓿地较棉花种植地(CK)的TOC、LFOC、HFOC和MBC分别表现出175.0%,1 416.0%,47.8%和216.0%的增长幅度,变化差异较为显著。在垂直剖面上,棉花种植地(CK)显著低于苜蓿地LFOC、POC、MBC含量,并随土层加深而不断降低。逐步回归分析表明LFOC与TOC显著正相关(p0.05)。苜蓿种植年限、土层以及这两个变量的交互作用对POC/TOC产生显著影响(p0.01),对TOC、LFOC、HFOC、POC、MBC、LFOC/TOC、HFOC/TOC和MBC/TOC均产生极显著影响(p0.001)。苜蓿种植提高了土壤质量,降低了土壤容重和盐碱性,连续种植14a是苜蓿最为合理的种植年限,同时苜蓿种植有利于0—60cm垂直土层有机碳组分的累积,尤其对TOC、LFOC和MBC的增长效果极其显著。

Characteristics of Soil Organic Carbon Fractions of Alfalfa Soils in the Minqin Oasis

A study was conducted in the Minqin Oasis of Wuwei city in Northwest China to understand the trend of soil organic carbon fractions and its influencing factors after several years of alfalfa planting in the Minqin Oasis.Three treatments were conducted,including 3 years (A3),14 years (A14),and 22 years (A22) continuous cropping of alfalfa.Content of total organic carbon (TOC),heavy fraction organic carbon (HFOC),light fraction organic carbon (LFOC),particulate organic carbon (POC),and microbial biomass carbon (MBC) in the soil were determined through field survey sampling and indoor laboratory analysis.The results showed that soil bulk density and electrical conductivity of 22 years alfalfa soil decreased by 13.9％ and 95.4％,respectively,compared with that of cotton soil.Compared with the cotton soil (CK),the TOC,LFOC,HFOC,and MBC of 3 years,14 years and 22 years alfalfa soil was significantly increased by 175.0％,1 416.0％,47.8 ％,and 216.0％,respectively.Vertical profile of cotton soil showed that content of LFOC,POC,MBC decreased with the increase of soil depth.Stepwise regression analysis showed that there was a significant positive correlation between LFOC and TOC (p＜0.05).Alfalfa planting age,soil layer and their interaction had a significant impact on POC/TOC (p＜0.01),and an extremely significant effect on TOC,LFOC,HFOC,POC,MBC,LFOC/TOC,HFOC/TOC,and MBC/TOC (p＜0.001).Alfalfa planting could improve soil quality and reduce soil bulk density and salinity.The study revealed that continuous planting for 14 years is the most reasonable planting time for alfalfa.Meanwhile,alfalfa planting is beneficial to the accumulation of organic carbon fractions in the 0-60 cm soil layer,especially to the increase of TOC,LFOC,and MBC.