Soil microbial biomass and diversity after herbicide application

Abstract

Greenhouse and field experiments were conducted to investigate the effects of herbicides on soil microbial C (microbial biomass), bacterial diversity and community structure. In the first greenhouse experiment, 12 herbicides were applied at recommended rates to a Gray Luvisolic soil contained in trays. Soil samples were collected 0, 1, 2, 3 and 4 wk after treatment and analysed for microbial C and bacterial diversity. The second greenhouse experiment was similar to the first, but only 6 of the 12 herbicides were applied to a Gray Luvisolic and Black Chernozemic soil. The same six herbicides were applied to the Gray Luvisolic soil at a field site near Fort Vermilion, Alberta, and to the Black Chernozemic soil at Lacombe, Alberta, in 2000. In the first greenhouse experiment, metribuzin, imazamox/imazethapyr, triasulfuron and metsulfuron methyl reduced microbial C compared with glufosinate ammonium and sethoxydim. In the second greenhouse experiment, microbial diversity as determined by Shannon index was lower after application of metribuzin, imazamox/imazethapyr and glufosinate ammonium than after application of glyphosate, but none of the herbicides altered microbial diversity relative to the control treatment. In the field experiments, herbicides had no effect on microbial C or diversity. In all experiments, examination of microbial community structure revealed herbicide-induced shifts in microbial composition even when diversity indices among treatments were not different. It was concluded that herbicides applied once at recommended rates did not have significant or consistent effects on microbial C or diversity. Key words: Environmental sustainability, substrate utilization, biological soil quality, community-level physiological profiles (CLPP)