N_2O and NO emission from agricultural fields and soils under natural vegetation:summarizing available measurement data and modeling of global annual emissions

摘要

The number of published N_2O and NO emissions measurements is increasing steadily,providing additional information about driving factors of these emissions and allowing an improvement of statistical N-emission models.We summarized information from 1008 N_2O and 189 NO emission measurements for agricultural fields,and 207 N_2O and 210 NO measurements for soils under natural vegetation.The factors that significantly influence agricultural N_2O emissions were N application rate,crop type,fertilizer type,soil organic C content,soil pH and texture,and those for NO emissions include N application rate,soil N content and climate.Compared to an earlier analysis the 20% increase in the number of N_2O measurements for agriculture did not yield more insight or reduced uncertainty,because the representation of environmental and management conditions in agro-ecosystems did not improve,while for NO emissions the additional measurements in agricultural systems did yield a considerable improvement.N_2O emissions from soils under natural vegetation are significantly influenced by vegetation type,soil organic C content,soil pH,bulk density and drainage,while vegetation type and soil C content are major factors for NO emissions.Statistical models of these factors were used to calculate global annual emissions from fertilized cropland (3.3 Tg N_2O-N and 1.4 Tg NO-N)and grassland (0.8 Tg N_20-N and 0.4 Tg NO-N).Global emissions were not calculated for soils under natural vegetation due to lack of data for many vegetation types.