Evidence for the importance of litter as a co-substrate for MCPA dissipation in an agricultural soil

Abstract

Environmental controls of 2-methyl-4-chlorophenoxyacetic acid (MCPA) degradation are poorly understood. We investigated whether microbial MCPA degraders are stimulated by (maize) litter and whether this process depends on concentrations of MCPA and litter. In a microcosm experiment, different amounts of litter (0, 10 and 20 g kg(-1)) were added to soils exposed to three levels of the herbicide (0, 5 and 30 mg kg(-1)). The treated soils were incubated at 20 °C for 6 weeks, and samples were taken after 1, 3 and 6 weeks of incubation. In soils with 5 mg kg(-1) MCPA, about 50 % of the MCPA was dissipated within 1 week of the incubation. Almost complete dissipation of the herbicide had occurred by the end of the incubation with no differences between the three litter amendments. At the higher concentration (30 mg kg(-1)), MCPA endured longer in the soil, with only 31 % of the initial amount being removed at the end of the experiment in the absence of litter. Litter addition greatly increased the dissipation rate with 70 and 80 % of the herbicide being dissipated in the 10 and 20 g kg(-1) litter treatments, respectively. Signs of toxic effects of MCPA on soil bacteria were observed from related phospholipid fatty acid (PLFA) analyses, while fungi showed higher tolerance to the increased MCPA levels. The abundance of bacterial tfdA genes in soil increased with the co-occurrence of litter and high MCPA concentration, indicating the importance of substrate availability in fostering MCPA-degrading bacteria and thereby improving the potential for removal of MCPA in the environment.

Gene-Centric Model Approaches for Accurate Prediction of Pesticide Biodegradation in Soils

“…Therefore, we used experimental data from previous studies to evaluate models’ performance. Short-term experiments showed that both 2,4-D and MCPA are readily degradable compounds which do not persist in soil. − Some experiments have reported no 2,4-D and MCPA residues or residues below detection limit after 1 to 5 weeks. ,− …”

Soil Microbial Community Changes in a Field Treatment with Chlorotoluron, Flufenacet and Diflufenican and Two Organic Amendments

“…Little is known about the effects these herbicides and organic residues have on the various groups of soil microorganisms when they are applied jointly. Most of the studies on soil microbial response to pesticides and organic residues have been assessed at laboratory or greenhouse scale [6,14,[22][23][24][25], but only a few assays have been performed at field scale [13,19]. Moreover, only one study has been found in the literature that refers to the impact on soil microbial activity of the combined application of the herbicide chlorotoluron with organic residues under field conditions [11].…”

Pethoxamid dissipation and microbial activity and structure in an agricultural soil: Effect of herbicide rate and organic residues

“…Also, it has been indicated a significant early impact and a relevant late impact on the bacterial community when the application of pethoxamid and glyphosate to soil was carried out (Valverde et al, 2014). Saleh et al (2016) have reported signs of toxic effects on soil bacteria at high herbicide (MCPA) concentrations. Karpouzas et al (2014) have reported the inhibitory effects of nicosulfuron on Actinobacteria at rates 20 times higher than the recommended ones.…”