Nitrous oxide fluxes from a grain–legume crop (narrow‐leafed lupin) grown in a semiarid climate

Abstract

Abstract 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 °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.