Effects of Pesticides on Nitrous Oxide Production in Sugarcane Cropping Soil

Abstract

This study aimed to assess the non-target impacts of pesticides on soil biological processes, particularly N2O emissions and improve understanding of the contributions of nitrification and denitrification to N2O production in sugarcane soils. We conducted a laboratory incubation experiment, in which a herbicide Roundup®, an insecticide Confidor®, a fungicide Shirtan®, and a fumigant metam sodium were added to a Ferrosol and then incubated at 25°C for 38 days at 2 moisture regimes (55 % and 90% water holding capacity (WHC)). At day 28, soil water contents in the 55% WHC treatments were also increased to 90% WHC to create a condition to favour denitrification. The 55% and 90% WHC treatments received NH4SO4 at 40µg N g−1 dry soil and KNO3 at 40µg N g−1 dry soil, respectively, with K15NO3 added at 2 µg N g−1 of dry soil in all treatments. Compared with the control treatment, Confidor application significantly increased net nitrification rates and N2O emissions at 55% WHC. After increasing water content from 55% to 90% WHC at day 28, net denitrification occurred in the metam sodium treatment; N2O emissions increased in the order: metam sodium > Shirtan > Glyphosate treatment, with little changes in the Confidor and control treatments. During the 38-day incubation at 90% WHC, the metam sodium treatment emitted more N2O emissions than other treatments in the first 15 days of the incubation but no significant differences were observed among the other treatments at the end of the incubation.