Herbage and nitrogen yields, fixation and transfer by white clover to companion grasses in grazed swards under different rates of nitrogen fertilization

D. Enriquez-Hidalgo*, T. J. Gilliland, D. Hennessy

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)peer-review

56 Citations (Scopus)

Abstract

In grass–legume swards, biologically fixed nitrogen (N) from the legume can support the N requirements of the grass, but legume N fixation is suppressed by additional fertilizer N application. This study sought to identify a fertilizer N application rate that maximizes herbage and N yields, N fixation and apparent N transfer from white clover to companion grasses under intensive grazing at a site with high soil-N status. During a 3-year period (2011–2013), swards of perennial ryegrass and of perennial ryegrass–white clover, receiving up to 240 kg N ha−1 year−1, were compared using isotope dilution and N-difference methods. The presence of white clover increased herbage and N yields by 12–44% and 26–72%, respectively. Applications of N fertilizer reduced sward white clover content, but the effect was less at below 120 kg N ha−1. The proportion of N derived from the atmospheric N fixation was 25–70%. Nitrogen fixation ranged from 25 to 142 kg N ha−1 measured using the isotope dilution method in 2012 and from 52 to 291 kg N ha−1 using the N-difference method across all years. Fertilizer N application reduced the percentage and yield of fixed N. Transfer of N from white clover to grass was not confirmed, but there was an increased N content in grass and soil-N levels. Under intensive grazing, the maximum applied N rate that optimized herbage and N yields with minimal effect on white clover content and fixation rates was 60–120 kg N ha−1.

Original languageEnglish
Pages (from-to)559-574
Number of pages16
JournalGrass and Forage Science
Volume71
Issue number4
DOIs
Publication statusPublished - 1 Dec 2016

Keywords

  • biological N fixation
  • intensive grazing
  • mixed sward
  • N production
  • perennial ryegrass
  • Trifolium repens L.

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