SPATIAL VARIABILITY OF NITROUS-OXIDE FLUXES IN MOWN AND GRAZED GRASSLANDS ON A POORLY DRAINED CLAY SOIL

Fluxes of nitrous oxide (N2O) were measured in mown and intensively-gr azed plots on a slightly-sloping, poorly-drained clay soil, using 144 flux chambers on four consecutive days. We tested the hypotheses that (i) spatial variability of N2O fluxes is larger in grazed than in mown grassland and (ii) spatial dependency is larger in mown than in graze d grassland. Distributions were approximately log-normal. Fluxes from grazed grassland were larger than those from mown grassland. Multiple linear regression analyses showed weak relationships between N2O flux and moisture, NH4+, NO3- and C contents, with less than 15% of the var iance in N2O flux accounted for. Spatial variability was large both on a relatively small scale (less than 6 m) and on a larger scale (10-10 0 m) and was larger on mown grassland than on grazed grassland. Geosta tistics showed that N2O fluxes were spatially dependent for a lag dist ance of less than 6 m on mown grassland. On grazed grassland fluxes we re spatially independent on a scale of < 6 m. The large spatial variab ility of N2O fluxes suggests that even measurement techniques that int egrate N2O fluxes over a large area may be hampered by the large spati al variability of N2O fluxes. Copyright (C) 1996 Elsevier Science Ltd