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Soil-plant nitrogen isotope composition and nitrogen cycling after biochar applications


Biochar has strong potential to improve nitrogen (N) use efficiency in both agricultural and horticultural systems. Biochar is usually co-applied with full rates of fertiliser. However, the extent to which N cycling can be affected after biochar application to meet plant N requirement remains uncertain. This study aimed to explore N cycling up to 2 years after biochar application. We applied pine woodchip biochar at 0, 10 and 30 t ha−1 (B0, B10, B30, respectively) in a macadamia orchard and evaluated the N isotope composition (δ15N) of soil, microbial biomass and macadamia leaves. Soil total N (TN) and inorganic N pools were also measured up to 2 years after biochar application. Biochar did not alter soil TN but soil NO3-N increased at months 12 and 24 after biochar application. Soil NO3-N concentrations were always over ideal levels of 15 μg g−1 in B30 throughout the study. Stepwise regression indicated that foliar δ15N decreases after biochar application were explained by increased NO3-N concentrations in B30. Foliar TN and photosynthesis were not affected by biochar application. The soil in the high rate biochar plots had excess NO3-N concentrations (over 30 μg g−1) from month 20 onwards. Therefore, N fertiliser applications could be adjusted to prevent excessive N inputs and increase farm profitability.

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The authors thank Newell family at Beerwah QLD, Griffith University and University of the Sunshine Coast. We thank Dr. Huang for loaning equipment. We also acknowledge the contribution of Mr Lambert, Dr Walton, Mr. Randall, Dr Abdullah, Dr Wang, Ms. Wang and Mr. Saavedra-Mella for their assistance throughout the study. The financial support was provided through internal grants received from the Griffith University and University of the Sunshine Coast.


This research was funded by internal grants from Griffith University and University of the Sunshine Coast.

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Fund: SHB; Research development: SHB, CYX, ZX, HW; Data analysis: LA, SHB, HW; Manuscript writing: LA, SHB, FR; Manuscript revision: LA, SHB, FR, CYX, ZX, HW

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Correspondence to Shahla Hosseini Bai.

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Asadyar, L., Xu, CY., Wallace, H.M. et al. Soil-plant nitrogen isotope composition and nitrogen cycling after biochar applications. Environ Sci Pollut Res 28, 6684–6690 (2021).

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  • Photosynthesis
  • Wood-based biochar
  • Nitrogen retention
  • Nitrogen isotope composition
  • Macadamia integrifolia