| Aiming at estimating the spatial variability in N2 fixation, and to evaluate the appropriateness of the 15N isotope dilution (ID) method and the natural 15N abundance (NA) method in reflecting spatial variability under the influence of cattle grazing, the symbiotic N2 fixation in grass-white clover mixture was studied. At the Foulum site, where the ID method was used, differences in the climatic conditions between the two years of investigations caused a considerable difference in plant growth rates and proportion of clover. Consequently, the total N2 fixation in ungrazed reference plots was significantly less in 1998 than in 1997, being 5.9 and 12.5 g N m-2, respectively. In both years there was a wide range in concentration of inorganic N in the soil... |
