Comparative Assessment of the Effect of Synthetic and Natural Fungicides on Soil Respiration

Angelo Stefani,Joanna D’Arc Felício,Mara M De Andréa

doi:10.3390/s120303243

Abstract

As toxic pesticide residues may persist in agricultural soils and cause environmental pollution, research on natural fungicides to replace the synthetic compounds is currently increasing. The effect of the synthetic fungicide chlorothalonil and a natural potential fungicide on the soil microbial activity was evaluated here by the substrate-induced respiration by addition of glucose (SIR), as bioindicator in two soils (Eutrophic Humic Gley—GHE and Typic Eutroferric Chernosol—AVEC). The induced soil respiration parameter was followed during 28 days after soil treatment either with chlorathalonil (11 μg·g−1), or the methanolic fraction from Polymnia sonchifolia extraction (300 μg·g−1), and 14C-glucose (4.0 mg and 5.18 Bq of 14C-glucose g−1). The 14C-CO2 produced by the microbial respiration was trapped in NaOH (0.1 M) which was changed each two hours during the first 10 h, and 1, 3, 5, 7, 14 and 28 days after the treatments. The methanolic fraction of the plant extract inhibited (2.2%) and stimulated (1.8%) the respiration of GHE and AVEC, respectively, but the synthetic chlorothalonil caused 16.4% and 2.6% inhibition of the respiration, respectively of the GHE and AVEC soils. As the effects of the natural product were statistically small, this bioindicator indicates that the methanolic fraction of the Polymnia sonchifolia extract, which has fungicide properties, has no environmental effects.

Highlights

One of the most important functions of soil microorganisms is the turnover of organic matter that happens mainly by the degradation of plant and animal debris and is reflected in the soil fertility and environmental quality [1,2,3]
There are pesticides that do not affect soil respiration [30], the GHE soil treated with chlorothalonil presented a statistically smaller production of 14C-CO2 (p = 0.001) than its untreated control from 8 h to one day after the fungicide treatment (Figure 1)
When the GHE was treated with the P. sonchifolia methanol fraction, the 14C-CO2 production presented statistically different results from the control (p = 0.001), the values were small but indicated a slightly stimulation by the plant extract

Summary

Introduction

One of the most important functions of soil microorganisms is the turnover of organic matter that happens mainly by the degradation of plant and animal debris and is reflected in the soil fertility and environmental quality [1,2,3]. The N fertilization [5], the soil moisture [6,7], soil temperature [8], and the presence of pesticide residues in the agricultural environment may disturb the natural degradation processes [9]. Some substrates, including pesticides, may inhibit, and stimulate the microbial activity [10]. Disturbances of the microbial activity may influence the important biogeochemical processes of the entire soil environment

Methods

Results

Conclusion