Abstract

Independent field and laboratory incubation experiments were conducted to investigate the effects of two commonly used herbicides butachlor and bensulfuron-methyl on N2O emissions from a dry-seeded rice field. Three treatments were applied in field experiments: a fertilized control without herbicide, fertilized plots amended with butachlor equivalent to 2.55 L ha−1 of 60 % by weight active ingredient and fertilized plots amended with bensulfuron-methyl equivalent to 300 g ha−1 of 10 % by weight active ingredient. Herbicides were applied twice in the rice growing season according to local farming practices. The same treatments were used in laboratory incubation experiments, i.e., a fertilized control without herbicide and fertilized soil amended with the herbicide butachlor or bensulfuron-methyl. The soil moisture was adjusted to 0.55 g g−1 in the lab incubation experiments based on the average water content determined in the dry-seeded rice field. The field and laboratory simulation experiments all showed that the butachlor applications led to significantly increased N2O emissions (p 0.05). Butachlor enhanced the N2O emissions by up to 177.5 % over the entire rice growing season. Moreover, butachlor and bensulfuron-methyl treatment led to a marginal stimulation of the soil respiration rates. A further investigation in the field experiments suggested that the butachlor-enhanced N2O emissions resulted from increased soil ammonium nitrogen and nitrate nitrogen contents and the more abundance of ammonia-oxidizing and denitrifying bacteria in the late stage after the herbicide application. The bensulfuron-methyl treatment had no influence on N2O emissions during the rice growing season, which was attributed to the low soil nitrate nitrogen contents during this period.

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