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

Leila Asadyar, Cheng Yuan Xu, Helen M. Wallace, Zhihong Xu, Frédérique Reverchon, Shahla Hosseini Bai

Research output: Contribution to journalArticlepeer-review


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.

Original languageEnglish
Pages (from-to)6684-6690
Number of pages7
JournalEnvironmental Science and Pollution Research
Issue number6
Publication statusPublished - Feb 2021
Externally publishedYes


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