Effects of fomesafen on soil microorganisms, soil enzyme activities and its degradation in soybean rhizosphere

Objectives The objective of this study is to provide foundation for further analysis of residual pollution of herbicides by investigating microecological effects of fomesafen and its degradation dynamics in the soybean rhizosphere.

Methods A pot experiment was conducted using rhizobox cultural method and soybean as test materials in a greenhouse. Fomesafen levels of 0 mg/kg (control), 3.75 mg/kg (low), 7.5 mg/kg (middle) and 18.75 mg/kg (high) were applied in rhizobox soil. The numbers of bacteria, fungi and actinomycetes and activities of catalase, phosphatase, urease and invertase in the rhizosphere of soybean were determined, and the degradation dynamics of the fomesafen in the soybean rhizosphere were studied.

Results Compared with control, the number of bacteria in the soybean rhizosphere was significantly decreased with low concentration fomesafen (P < 0.05), significantly higher with high concentration on the 28th day (P < 0.05), and no significant difference with middle concentration. There was no significant difference in the numbers of fungi and actinomycetes in the soybean rhizosphere between the fomesafen treatments and control. The activity of catalase was not significantly affected; the urease activity was significantly decreased with low concentration fomesafen, and increased at the first and then decreased with the middle and high concentrations; the activity of invertase with high concentration fomesafen was significantly lower than that with control (P < 0.05) on the 42nd and 56th days. The degradation dynamics of the three concentrations of fomesafen treatments in rhizospheric soil were all accorded with the first-order kinetics equation, with the degradation half-life period from the 99 to 231 d. The degradation of high concentration fomesafen was faster than those of the low and middle concentrations in rhizospheric soils.

Conclusions Fomesafen has no significant impact on the number of bacteria, fungi and actinomycetes in the soybean rhizosphere, except that low concentration of fomesafen will significantly decrease the number of bacteria. Fomesafen has no adverse impact on catalase activity, decreases phosphatase activity in a short time, significantly decreases urease activity at low concentration, and significantly decreases invertase activity at high concentration in the end of experiment. The higher the initial applied concentration of fomesafen is, the faster the degradation and the shorter the half-life will be in the soybean rhizosphere.