干旱区生态环境知识资源中心

Understanding nitrous oxide (N(2)O) fluxes from grain-legume crops in semiarid and arid regions is necessary if we are to improve our knowledge of global terrestrial N(2)O losses resulting from biological N(2) fixation. N(2)O fluxes were measured from a rain-fed soil, cropped to a grain-legume in a semiarid region of southwestern Australia for 1 year on a subdaily basis. The site included plots planted to narrow-leafed lupin (Lupinus angustifolius; ’lupin’) and plots left bare (no lupin). Fluxes were measured using soil chambers connected to a fully automated system that measured N(2)O by gas chromatography. Daily N(2)O fluxes were low (-0.5 to 24 g N(2)O-N ha-1 day-1) and not different between treatments, culminating in an annual loss of 127 g N(2)O-N ha-1. Greatest daily N(2)O fluxes occurred from both treatments in the postharvest period, and following a series of summer and autumn rainfall events. At this time of the year, soil conditions were conducive to soil microbial N(2)O production: elevated soil water contents, increased inorganic nitrogen (N) and dissolved organic carbon concentrations, and soil temperatures generally > 25 degrees C; furthermore, there was no active plant growth to compete for mineralized N. N(2)O emissions from the decomposition of legume crop residue were low, and approximately half that predicted using the currently recommended IPCC methodology. Furthermore, the contribution of the biological N(2) fixation process to N(2)O emissions appeared negligible in the present study, supporting its omission as a source of N(2)O from the IPCC methodology for preparing national greenhouse gas inventories.