Effects of the herbicides butachlor and bensulfuron-methyl on NO emissions from a dry-seeded rice field.

Independent field and laboratory incubation experiments were conducted to investigate the effects of two commonly used herbicides butachlor and bensulfuron-methyl on NO 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 of 60 % by weight active ingredient and fertilized plots amended with bensulfuron-methyl equivalent to 300 g ha 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 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 NO emissions ( p < 0.05), whereas bensulfuron-methyl had no effect on NO emissions ( p > 0.05). Butachlor enhanced the NO 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 NO 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 NO emissions during the rice growing season, which was attributed to the low soil nitrate nitrogen contents during this period. [ABSTRACT FROM AUTHOR]