Pedosphere 31(1): 204--213, 2021
ISSN 1002-0160/CN 32-1315/P
©2021 Soil Science Society of China
Published by Elsevier B.V. and Science Press
Chemical and spectroscopic characteristics of humic acid from a clay loam soil in Ontario after 52 years of consistent fertilization and crop rotation
Nan ZHAO1, Xixiang YANG2, Guocheng HUANG1, Yizhong LÜ3, Jing ZHANG4, Yuanyuan FAN3, Craig F. DRURY5, Xueming YANG5
1School of Environmental Science and Engineering, Sun Yat-sen University, Guangzhou 510275(China)
2School of Chemistry, Guangzhou Key Laboratory of Analytical Chemistry for Biomedicine, South China Normal University, Guangzhou 510006(China)
3College of Resources and Environmental Sciences, China Agricultural University, Beijing 100193(China)
4Key Laboratory of Environmental Nano-Technology and Health Effect, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085(China)
5Harrow Research and Development Centre, Agriculture and Agri-Food Canada, Harrow, Ontario N0R 1G0(Canada)
      Long-term fertilization and crop rotation can influence both organic C sequestration as well as the C composition of soils and the more resistant organic C compounds contained in humic acid (HA). This study examined the effects of fertilization and cropping type (monoculture corn (MC) and Kentucky bluegrass sod (KBS) and corn-oat-alfalfa-alfalfa rotation (RC)) on the HA composition of soil from a 52-year field study in southern Ontario, Canada. Humic acid samples were extracted from soil, and elemental analysis, infrared spectroscopy, solid state 13C nuclear magnetic resonance spectra, and electron paramagnetic resonance methods were used to determine the influence of the cropping type on the characteristics of HA. Both fertilization and cropping type affected the chemical characteristics of HA. Fertilization led to a 5.9% increase in C, a 7.6% decrease in O, and lower O/C and (N + O)/C ratios in HA as compared to the corresponding non-fertilized treatments. Rotation resulted in a lower proportion of C (48.1%) and a greater (N + O)/C ratio (0.7) relative to monoculture cropping. Infrared spectroscopy analysis showed that HA contained more C-O groups in fertilized soil than in non-fertilized soil under MC and KBS. Fertilization increased the O-alkyl-C, phenolic-C, and free radical contents of HA relative to non-fertilization treatments. Rotation decreased the aliphatic and carboxyl groups and increased the O-alkyl, carbohydrate, aryl, and phenolic groups and free radicals, relative to MC and KBS. Both long-term crop rotation and fertilization dramatically modified the soil HA composition. Significant relationships were observed between the molecular composition of HA and soil organic C. Hence, humic acid characterization could be used as an indicator of the long-term sustainability of crop management practices.
Key Words:  corn,humification process,infrared spectroscopy,Kentucky bluegrass sod,molecular composition,soil organic C
Citation: Zhao N, Yang X X, Huang G C, Lü Y Z, Zhang J, Fan Y Y, Drury C F, Yang X. 2021. Chemical and spectroscopic characteristics of humic acid from a clay loam soil in Ontario after 52 years of consistent fertilization and crop rotation. Pedosphere. 31(1): 204-213.
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