Spatial variability of N N2O emissions and contributing soil factorsfrom an Australian irrigated dairy pasture2O

摘要

One of the main causes for the uncertainty in quantifying nitrous oxide (N2O) emissions from soils is the large spatial variability.This study was designed toinvestigate the extent of spatial variability of N2O emissions in an irrigated,grazed pastureand the contributing mechanisms.100 minichambers (15 cm diameter) were placedover ~1 ha of irrigated dairy pasture in southeastern Australia to measure N2O fluxes.Soil properties (soil moisture,bulk density,pH,mineral N,total N and C) under eachchamber were measured.Nitrous oxide fluxes and soil variables were analysed using geostatisticsto discern the spatial patterns and to examine effects of soil properties on N2Oemissions.The experiment was conducted twice,in February and in April 2004,soon aftertwo separate events of urea application with follow-up irrigation.The spatial variationof N2O fluxes was huge,ranging from 20 to 900 ngN- N2O m-2 s-1 and the N2O fluxesshowed spatial autocorrelation below 77 and 74m,respectively.The average N2O fluxesfrom the 100 minichambers were 160 and 143 ng N- N2O m-2 s-1 for the two experiments.Fluxes were most strongly correlated with soil nitrate ( NO3-).The soil NO NO33-concentration was the dominant variable contributing to the spatial variability of N2Ofluxes,accounted for 60% the variability observed because soil water and C were closeto the optimum condition for denitrification.The average minichamber fluxes were compared with fluxes measured by automaticchambers installed at the site as well as by micrometeorological techniques.Averagefluxes from the mini chambers compared well with those of the large auto-chambers,however micrometeorological and mini chamber results were not in agreement.