Below-ground nitrogen transfer between different grassland species: direct quantification by 15N leaf feeding compared with indirect dilution of soil 15N

Henning Høgh Jensen, Jan K. Schjoerring

Research output: Contribution to journalJournal articleResearchpeer-review

Abstract

Nitrogen (N) transfer from one species to another is important for the N cycling in low-input grassland. In the present work, estimates obtained by an indirect N-15 dilution technique were compared with estimates obtained by a direct N-15 leaf feeding technique over two complete growing seasons in red clover-ryegrass and white clover-ryegrass mixtures under field conditions.

The direct technique confirmed that N transfer between clovers and ryegrass is a bi-directional process. The transfer of N from both clovers to ryegrass occurred within 25 days upon the first labelling event. A very high N transfer occurred from white clover to the associated ryegrass, 4.5 and 7.5 g m(-2) in the 1st and 2nd production year, respectively. The corresponding values for transfer from red clover to the associated ryegrass were 1.7 and 3.6 g m(-)2. Quantified relatively to the total above-ground N content of white clover- ryegrass and red clover-ryegrass mixtures, the N transfer exceeded 50% and 10%, respectively, in three out of seven harvests. The N transfer from N-15 labelled grass to associated clovers constituted a relatively constant proportion of approx. 8% of the above-ground N content of the mixtures.

Estimates based on the soil N-15 dilution technique generally underestimated the net N transfer by more than 50% compared to the direct N-15 labelling technique. Furthermore, the indirect N-15 dilution technique estimated only marginal differences between red and white clover in the quantities of N transferred, whereas the direct N-15 labelling technique showed the N transfer from white clover to the associated ryegrass to be significantly higher than that involving red clover. It is concluded that N transfer is a much more dynamic and quantitatively important process in grassland than previously recognised.
Original languageEnglish
JournalPlant and Soil
Volume227
Issue number1-2
Pages (from-to)171-183
ISSN0032-079X
DOIs
Publication statusPublished - 2000
Externally publishedYes

Keywords

  • Clover
  • Direct 15N leaf labelling
  • Facilitation
  • Grassland
  • 15N isotope dilution
  • Nitrogen transfer
  • Ryegrass

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