ifoam'96 ifoam'96
Book of Abstracts
11th IFOAM Scientific Conference
11-15 August 1996, Copenhagen, Denmark
EcoWeb Denmark


Biological Nitrogen Fixation in an Organic System. P2; 77

Vinther, F. P.1 & Jensen, E. S.2

1Dept. of Soil Science, Danish Institute of Plant and Soil Science, Research Centre Foulum, DK-8830 Tjele, Denmark and 2Environmental Science and Technology Department, Risø National Laboratory, DK-4000 Roskilde, Denmark

Biological nitrogen fixation (BNF) is a prerequisite for sustainable organic farming, being the most important input of N to the system. The leguminous crops, with grass-clover pastures as the major crop, also often constitute more the half
of the area in Danish organic farming systems. Measurements of BNF have been carried out during two years in an organic farming system at Research Centre Foulum. The system consist of a six year crop rotation, and includes a 1st and 2nd year grass-clover pasture grazed by cattle and a barley-pea crop. The BNF in the grass-clover pastures are estimated using a three step procedure:
1) In sub-plots, which are not grazed, BNF is determined using 15N-dilution techniques,
2) in parallel experiments effects of grazing/cutting and of urine and dung patches on BNF are determined using 15N-dilution as well as acetylene reduction techniques, and 3) based on statistical information on distribution and frequency of urine and dung patches in the field, total BNF in the grass-clover pastures are estimated. Results from these experiments along with results of the contribution of BNF to the associated grass and to the subsequent crop in the cropping system are presented.

Søgaard, K.; Petersen, S. O. & Vinther, F. P. (1996): The effect of N in urine on herbage production, N-fixation and ammonia volatilization. 16th General Meeting of the European Grassland Federation, 15-19 Sep, Grado, Italy (in press).