Microbial respiration in soils of the Argentine Pampas after metsulfuron methyl, 2,4-D, and glyphosate treatments

Short-term response of microbial respiration after treatment with different doses of the herbicides metsulfuron methyl (MET), 2,4-D, and glyphosate (GLY) was studied in microcosms of soils collected in three agricultural sites of the Southern Pampas region, Buenos Aires, Argentina. The influence of diammonium phosphate [(NH4)(2)PO4] on carbon dioxide (CO2) evolution, when applied with the highest doses of the herbicides, was also investigated. MET had no effect on microbial respiration of an acidic soil of San Romn (pH 6.06), even at the highest rate. However, MET inhibited microbial respiration in soils of Bordenave (pH 7.44), at a rate of 0.1 mg kg(-1) soil. Low application rates of GLY and 2,4-D produced only transitory effects on CO2 evolution, whereas the addition of high doses of these herbicides stimulated microbial activity. On the other hand, the addition of fertilizer to soil treated with a high dose of GLY temporarily inhibited CO2 release.