Pedosphere 32(4): 629--636, 2022
ISSN 1002-0160/CN 32-1315/P
©2022 Soil Science Society of China
Published by Elsevier B.V. and Science Press
Nitrogen fertilization degrades soil aggregation by increasing ammonium ions and decreasing biological binding agents on a Vertisol after 12 years
Zichun GUO1, Wei LI2, Mahbub UL ISLAM1,3,4, Yuekai WANG1,3, Zhongbin ZHANG1, Xinhua PENG1,3
1State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008 (China)
2Crop Research Institute, Anhui Academy of Agricultural Sciences, Hefei 230031 (China)
3University of Chinese Academy of Sciences, Beijing 10049 (China)
4Bangladesh Agricultural Research Institute, Gazipur 1701 (Bangladesh)
      Degraded soil aggregation arising from nitrogen (N) fertilization has been reported in many studies; however, the mechanisms have not yet been clarified. Elucidating the impact of N fertilization on soil aggregation would help to improve soil structure and sustain high crop production. The objective of this study was to determine the impact of long-term N fertilization on soil aggregation and its association with binding and dispersing agents. A 12-year (2008-2019) N fertilization field experiment on a Vertisol was performed, covering a wide range of N application rates (0, 360, 450, 540, 630, and 720 kg ha-1 year-1) and including straw management (straw return and straw removal) in a wheat (Triticum aestivum L.)-maize (Zea mays L.) cropping system. Soil samples of 0-20 cm depth were collected from 12 field treatments with 3 replications in 2019. Soil aggregate stability (mean weight diameter (MWD)) and contents of soil organic carbon (SOC), glomalin-related soil protein (GRSP), microbial biomass carbon (MBC), and mineral N (NH4+ and NO3-) were determined. Long-term N fertilization under straw removal conditions reduced soil MWD by 12%-18% at N rates from 0 to 720 kg ha-1 compared to that under straw return (P < 0.05). Soil MWD was positively associated with pH (P < 0.05) and MBC (P < 0.05), but negatively correlated with NH4+ (P < 0.05) and NO3- (P < 0.05). Compared with the straw removal treatment, the straw incorporation treatment significantly improved the contents of aggregating agents (SOC, GRSP, and MBC) (P < 0.001), but did not affect that of the dispersing agent (NH4+) (P > 0.05); consequently, it improved soil aggregation. Overall, our results indicate that long-term N fertilization may degrade soil aggregation because of the increases in monovalent ions (H+ and NH4+) and the decrease in MBC during soil acidification, especially when the applied N dose exceeded 360 kg ha-1 year-1. Our finding can minimize the negative structural impacts on Vertisol.
Key Words:  aggregating agents,aggregate stability,long-term nitrogen fertilization,soil structure,straw incorporation
Citation: Guo Z C, Li W, Ul Islam M, Wang Y K, Zhang Z B, Peng X H. 2022. Nitrogen fertilization degrades soil aggregation by increasing ammonium ions and decreasing biological binding agents on a Vertisol after 12 years. Pedosphere. 32(4): 629-636.
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