Nitrous oxide emission from herbicide-treated soybean

The emission of N2O from soybean plants treated with the herbicides dichlor ophenoxyacetic acid (2,4-D) and bromoxynil was studied. The N2O flux from 2 ,4-D- and bromoxynil-treated soybean was 14.1 ng N2O-N g(-1) fresh weight h (-1) and 19.7 ng N2O-N g(-1) fresh weight h(-1), respectively, i.e. approxi mately twice that of the controls. The NO2--N concentration in 2,4-D- and i n bromoxynil-treated soybean was about 8 mug N g(-1) fresh weight, i.e. fiv efold the concentration found in control plants. The NO3- content in herbic ide-treated soybean did not differ significantly from that of the control p lants. Consequently, the accumulation of NO2--N during the assimilation of NO3--N was thought to cause the observed N2O release. Probably, N2O is a by -product produced during either the reaction of NO2--N with plant metabolit es or NO2--N decomposition. Final conclusions must await further experiment s.