SOIL MICROBIAL ACTIVITY UNDER CHEMICAL FALLOW CONDITIONS - EFFECTS OF 2,4-D AND GLYPHOSATE

Field and laboratory studies were made to examine the effects of 2,4-D and glyphosate on soil microbial activity under zero-tillage chemical fallow conditions. Glyphosate and 2,4-D applied three consecutive times at field rates and 10 times the field rates had no effect on microbial biomass-C, C mineralization or nitrification in the field. Laboratory studies showed that 2 and 100 times the field rate of 2,4-D reduced nitrification by 11 and 79%, respectively. In laboratory studies, 2,4-D incorporated into the soil reduced nitrification, but surface-applied 2,4-D did not. Glyphosate and 2,4-D used as recommended should not affect microbial activity under dryland zero-tillage chemical fallow conditions.