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Book of Abstracts

11th IFOAM
Scientific Conference
11-15 August 1996
Copenhagen, Denmark

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Biological Nitrogen Fixation in Pastures S11

Jensen, E. S.1 ; Høgh-Jensen, H.2 ; Jørgensen, F. V.1 ; Schjørring, J. K.2 & Vinther, F. P.3

1) Environmental Science and Technology Department, Risø National Laboratory, DK-4000 Roskilde; 2) Department of Agricultural Sciences, The Royal Veterinary and Agricultural University of Copenhagen, DK-1871 Frederiksberg; 3Department of Soil Science, Research Centre Foulum, DK-8830 Tjele

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Biological nitrogen fixation (BNF) in grass/clover pastures constitutes the most important input of N in organic farming systems. The BNF in pastures can be managed by the farmer, although it is more difficult than the use of organic and inorganic fertilizers. Management of BNF is necessary to secure an adequate supply of N in the cropping system, to maintain soil fertility and to minimize the losses of N from the system. Several agronomic and environmental factors influence the N dynamics within the grass/clover pasture (Frame and Newbould, 1986). The most important factors are: the legume persistence and production, the soil N status and the competition with the associated grass (Ledgard and Steele, 1992).

The aim of the study was to obtain an improved understanding of the N dynamics within perennial ryegrass (Lolium perenne L.)/white clover (Trifolium repens L.) pastures for grazing in order to develop strategies to ensure an adequate supply of N into the cropping systems and reduce losses of N to the wider environment. Processes in the N-cycle were quantified using 15N-isotope techniques.

In a grazed system BNF is influenced by both the grazing frequency and animal excreta. However, only limited information is available on these effects and their interaction. We will focus on the effects of pasture composition/age and soil N status on BNF and N transfer from clover to associated grass.

Frame, J. & Newbould, P. (1986): Agronomy of white clover. Advances in Agronomy, 40, 1-88.

Ledgard, S. F. & Steele, K. W. (1992): Biological nitrogen fixation in mixed legume/grass pastures. Plant and Soil, 141, 137-153.