NOx emission from soils and its consequences for the atmosphere and biosphere: critical gaps and research directions for the future

Since the first paper on soil NOx emissions was published in 1978, the understanding of NOx flux from soil has grown enormously. While rapid strides have been made, progress across the suite of disciplines required to understand NOx emission, transport, chemistry, and deposition has been uneven and has resulted in gaps in knowledge and, indeed, somewhat conflicting ideas about the regional and global importance of NOx from soils. This paper summarizes some of the findings of the papers presented at the 1996 Tsukuba NOx workshop and suggests gaps in knowledge that may limit estimation and management of NOx emissions from soils. I discuss the causes and consequences of uncertainties in global estimates of soil NOx emissions and argue for use of process simulation models for NOx estimates. I also suggest three other missing pieces that limit our understanding of and ability to predict or manage NOx fluxes: 1) information on canopy uptake of NOx emitted from soils; 2) information on NOx response to agricultural management practices and approaches for simulating those high resolution effects; and 3) information on the consequences of atmospheric transport and deposition of anthropogenic nitrogen on NOx emissions from soils.