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应用生态学报 ›› 2022, Vol. 33 ›› Issue (11): 3037-3045.doi: 10.13287/j.1001-9332.202211.026

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顺磁物质对土壤低场核磁共振信号特征及含水量测定的影响

马红娇1,2, 马东豪1*, 刘志鹏3, 张佳宝1, 姜晓文4, 陆荣生4   

  1. 1中国科学院南京土壤研究所, 土壤与农业可持续发展国家重点实验室, 南京 210008;
    2中国科学院大学, 北京 100049;
    3南京农业大学资源与环境科学学院, 南京 210095;
    4东南大学, 江苏省微纳生物医疗器械设计与制造重点实验室, 南京 211189
  • 收稿日期:2022-01-18 修回日期:2022-08-25 出版日期:2022-11-15 发布日期:2023-05-15
  • 通讯作者: *E-mail: dhma@issas.ac.cn
  • 作者简介:马红娇, 女, 1997年生, 硕士研究生。主要从事土壤结构及水文过程研究。E-mail: mhjll05@163.com
  • 基金资助:
    国家自然科学基金项目(42177292)、中国科学院战略性先导科技专项(XDA28010401-6)和现代农业产业技术体系专项资金(CARS-03,CARS-52)

Effects of paramagnetic material on the characteristics of low field nuclear magnetic resonance signals and water measurement in different textured soils.

MA Hong-jiao1,2, MA Dong-hao1*, LIU Zhi-peng3, ZHANG Jia-bao1, JIANG Xiao-wen4, LU Rong-sheng4   

  1. 1State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, China;
    2University of Chinese Academy of Sciences, Beijing 100049, China;
    3College of Resources and Environmental Science, Nanjing Agricultural University, Nanjing 210095, China;
    4Jiangsu Key Laboratory for Design and Manufacture of Micro-Nano Biomedical Instruments, Southeast University, Nanjing 211189, China
  • Received:2022-01-18 Revised:2022-08-25 Online:2022-11-15 Published:2023-05-15

摘要: 核磁共振(NMR)技术由于具有高效快速、不破坏土壤结构且对人体无害等优点,逐渐被应用到土壤学相关领域研究中。然而,土壤中顺磁物质的存在对核磁共振信号特征的影响仍不明确。本研究旨在揭示顺磁物质对不同类型土壤低场核磁共振(LF-NMR)信号特征和土壤含水量测定的影响。结果表明:土壤水的LF-NMR信号量最高可达150左右,土壤矿物、有机质和微生物等固相物质的LF-NMR信号量基本不超过0.3,相对可以忽略。质地和顺磁物质对土壤水的LF-NMR信号量测量有更大影响。LF-NMR仪器存在弛豫时间监测盲区,信号量损失主要是由于顺磁物质加速了水中氢质子的弛豫过程,导致小孔隙中水分反馈的极快的LF-NMR信号不能被监测设备捕获。对于顺磁物质含量较少的壤性潮土(1.2%)和黏壤性黑土(1.3%),LF-NMR信号量损失不大,其与土壤含水量呈线性关系;但对于黏粒含量(45.3%)和顺磁物质含量(4.0%)较高的黏性红壤,测定中会损失一部分LF-NMR信号量,监测到的LF-NMR信号量与土壤含水量不再呈线性关系。此外,外源添加顺磁物质(3.0 g·L-1的MnCl2溶液)也会降低黑土和红壤中可被监测的LF-NMR信号量,黑土和红壤的信号量最大损失率分别为41.0%和46.7%,极大地改变其与土壤含水量之间的定量关系。因此,在利用LF-NMR测量富含顺磁物质(>1.3%)或有外源顺磁物质进入的黏性土壤的含水量时,应先通过校正降低顺磁物质等对LF-NMR信号量的影响。研究结果对利用低场核磁共振技术准确分析土壤水分分布及土壤孔隙结构具有重要意义。

关键词: 低场核磁共振, 顺磁物质, 弛豫时间, 土壤含水量, 黏粒含量

Abstract: Nuclear magnetic resonance (NMR) technology has been applied in soil science due to the characte-ristics of high efficiency, rapidity, no damage to soil structure, and harmlessness to the human body. However, the effect of the presence of paramagnetic materials in soils on the characteristics of NMR signals was still unclear. In this study, we investigated the effects of paramagnetic material on the low field nuclear magnetic (LF-NMR) signals and soil water content measurement in soils with different texture. The results showed that the LF-NMR signal of soil water could reach about 150, while that of all the solid materials including soil minerals, organic matter and microbes was less than 0.3, which was relatively negligible. Compared with the NMR signals produced by solid materials in soils, soil texture and paramagnetic material had stronger impact on the measured LF-NMR signals of soil water. LF-NMR equipment had a relaxation time monitoring blind area, and the loss of NMR signal was mainly due to the acceleration of the relaxation process of hydrogen protons in water by magnetic materials, resulting in extremely fast LF-NMR signals feed back by water in small pores that could not be captured by monitoring equipment. For loamy fluvo-aquic soil (1.2%) and clay loamy black soil (1.3%) with low paramagnetic material contents, the loss of LF-NMR signals was not large, which was linearly related to soil water content. For clayey red soil with high content of clay (45.3%) and paramagnetic materials (4.0%), a part of the LF-NMR signals would be lost in the measurement, and the monitored LF-NMR signal was not linearly related to the soil water content. In addition, external addition of paramagnetic materials (3.0 g·L-1 MnCl2 solution) would further reduce the LF-NMR signals that could be monitored in black and red soils. The maximum signal loss rates of black soil and red soil were 41.0% and 46.7%, respectively, which greatly changed the quantitative relationship between it and soil water content. Therefore, the influence of paramagnetic materials on the LF-NMR signals should be reduced first through correction when using LF-NMR to measure the water content of clay soil with rich internal paramagnetic materials (>1.3%) or external addition of paramagnetic materials. Our results would provide valuable insights into the study of soil water content measurement and soil pore structure analysis using low field nuclear magnetic resonance technology.

Key words: low-field nuclear magnetic resonance, paramagnetic material, relaxation time, soil water content, clay content