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In situ nitrous oxide and dinitrogen fluxes from a grazed pasture soil following cow urine application at two nitrogen rates

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posted on 2023-05-03, 20:50 authored by Keren DingKeren Ding, Jiafa LuoJiafa Luo, Timothy Clough, Stewart LedgardStewart Ledgard, Stuart LindseyStuart Lindsey, Hong Di
Cattle grazing of pastures deposits urine onto the pasture soil at high nitrogen (N) rates that exceed the pasture's immediate N demands, increasing the risk of N loss. Nitrous oxide (N2O), a greenhouse gas, and dinitrogen (N2) are lost from the cattle urine patches. There is limited information on the in situ loss of N2 from grazed-pasture systems which is needed for understanding pasture soil N dynamics and balances. The 15N flux method was used to determine N2 and N2O fluxes over time following synthetic urine-15N application at either 400 or 800 kg N ha−1 to a grazed perennial pasture soil. Results showed that daily N2O fluxes were higher under 800 kg N ha−1 than under 400 kg N ha−1, but there was no significant difference in N2 fluxes. Cumulative N2O emissions from soil with 400 kg N ha−1 and 800 kg N ha−1 applied represented 0.16 ± 0.08% and 0.43 ± 0.08% of deposited N, respectively, while emitted N2 accounted for 32.1 ± 4.1% and 14.4 ± 1.7%, respectively, over 95 days after urine application. Codenitrification and denitrification co-occurred, with denitrification accounting for 97.9 to 98.5% of total N2 production. Recovery of urine-15N in pasture decreased with increasing N rate with 14.7 ± 0.5% and 9.9 ± 0.8% recovered at 400 and 800 kg N ha−1, respectively after 95 days. The N2O/(N2 + N2O) product ratio was generally higher during periods of nitrification of urine-N (the first month after urine application) but with no clear relationship to other measured variables. Contrary to our hypothesis, an elevated urine-N rate did not enhance N2 loss. This is speculated to be due to enhanced ammonia volatilisation and transfer of N as nitrate, to deeper soil layers. Soil relative gas diffusivity indicated that high N2 fluxes resulted from entrapped N2 diffusing from the draining soil.

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© 2022 Elsevier Ltd. All rights reserved.

Language

  • English

Does this contain Māori information or data?

  • No

Publisher

Elsevier

Journal title

Science of The Total Environment

ISSN

0048-9697

Citation

Ding, K., Luo, J., Clough, T. J., Ledgard, S., Lindsey, S., & Di, H. J. (2022). In situ nitrous oxide and dinitrogen fluxes from a grazed pasture soil following cow urine application at two nitrogen rates. Science of The Total Environment, 838(4), 156473. https://doi.org/10.1016/j.scitotenv.2022.156473

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