Impacts of soil fumigation on greenhouse gas emission

Agricultural soils are a major source and/or sink for atmospheric greenhouse gases: nitrous oxide (N2O), carbon dioxide (CO 2), and methane (CH4). The production and consumption of these gases are directly linked to microbial activities. Soil fumigation, a common practice in agriculture to control soil-borne diseases and pests, affects a variety of soil organisms, including microbes. It was initially hypothesized that if soil fumigants were biocides there would be strictly negative impacts. However, the findings of this research indicated that there were stimulation effects as well, particularly for N2O production following chloropicrin (CP) fumigation. This was the first study that systematically quantified impacts of soil fumigation with CP and methyl isothiocyanate (MITC) on greenhouse gas exchange.; For N2O, increases in surface emissions from 7- to 12-fold were observed following fumigation with CP. The stimulation was confirmed in both laboratory and field experiments. Microbial activities contributed 82% to the CP-induced N2O production, with 18% from abiotic processes. Inhibitor studies suggested that fungal mediated denitrification reactions under aerobic conditions were the primary mechanisms for CP-induced N 2O production. There were no significant differences in N2O production following CP fumigation under various levels of acetylene (0 Pa, 10 Pa, and 10 kPa), suggesting that traditional nitrification and denitification reactions did not significantly contribute to N2O production after CP fumigation. 15N labeled studies indicated that 12% of N from CP was incorporated into N2O. No enrichment in N2 was observed, indicating that N2O was a terminal mineralization product of CP. Field measurements also illustrated a 4-fold increase in N 2O emissions following MITC fumigation. This stimulation effect was not observed in laboratory incubations under aerobic conditions.; There were slight reductions in CO2 emissions following both MITC and CP fumigation. The initial decreases were followed by an increase in CO2 emissions observed at 48 days resulting from the mineralization of the killed biomass from fumigation.; All fumigants tested significantly reduced CH4 oxidation rates in historically nonfumigated soils. However, fumigation with MITC increased CH4 oxidation rates in all historically MITC fumigated soils compared to controls. CP universally decreased oxidation capacity regardless of fumigation history.