Mechanisms of nitrogen transfer in a model clover-ryegrass pasture: a 15 N-tracer approach

Michaela K. Reay, Katrina A. Pears, Alison Kuhl, Richard P. Evershed, Phillip J. Murray, Laura M. Cardenas, Jennifer A. J. Dungait, Ian D. Bull*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

4 Citations (Scopus)
22 Downloads (Pure)


: Purpose : Nitrogen (N) transfer from white clover (Trifolium repens cv.) to ryegrass (Lolium perenne cv.) has the potential to meet ryegrass N requirements. This study aimed to quantify N transfer in a mixed pasture and investigate the influence of the microbial community and land management on N transfer. Methods: Split root 15N-labelling of clover quantified N transfer to ryegrass via exudation, microbial assimilation, decomposition, defoliation and soil biota. Incorporation into the microbial protein pool was determined using compound-specific 15N-stable isotope probing approaches. Results: N transfer to ryegrass and soil microbial protein in the model system was relatively small, with one-third arising from root exudation. N transfer to ryegrass increased with no microbial competition but soil microbes also increased N transfer via shoot decomposition. Addition of mycorrhizal fungi did not alter N transfer, due to the source-sink nature of this pathway, whilst weevil grazing on roots decreased microbial N transfer. N transfer was bidirectional, and comparable on a short-term scale. Conclusions: N transfer was low in a model young pasture established from soil from a permanent grassland with long-term N fertilisation. Root exudation and decomposition were major N transfer pathways. N transfer was influenced by soil biota (weevils, mycorrhizae) and land management (e.g. grazing). Previous land management and the role of the microbial community in N transfer must be considered when determining the potential for N transfer to ryegrass.
Original languageEnglish
Pages (from-to)369-389
Number of pages21
JournalPlant and Soil
Issue number1-2
Early online date28 Jul 2022
Publication statusPrint publication - Nov 2022


  • Nitrogen transfer
  • 15N-stable isotope probing
  • Soil microbial community
  • Clover
  • N-stable isotope probing


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