Effects of pesticides on activities of enzymes and microorganisms in a clay soil

Impact of an organic formulation (panchakavya) on the bioleaching of copper and lead in contaminated mine soil

The study was aimed to evaluate the potential of organic formulation, panchakavya, for enhancing the biological leaching of Pb and Cu in contaminated mine soil. Response surface methodology based Box-Behnken design was used to optimize the variables such as incubation time, panchakavya concentration, and agitation rate. The maximum bioleaching (Pb=64% and Cu=49%) was observed after 54 h of incubation with 10 mL panchakavya at 120 rpm. Statistics-based contour and three-dimensional plots were generated to understand the relationship between Pb and Cu bioleaching and variables. High-performance liquid chromatography analysis showed the presence of lactic (25.88 mg g(-1)), citric (0.14 mg g(-1)), succinic (0.14 mg g(-1)), malic (0.66 mg g(-1)), and acetic (0.44 mg g(-1)) acids in panchakavya, which may have a vital role in the removal of metals from the contaminated soil. Soil fraction studies indicate a significant increase of Pb (45%) in the exchangeable fraction of panchakavya-treated soil. XRD studies confirmed the role of panchakavya induced calcite and other minerals in the precipitation of metal ions. A significant increase in the enzyme activities of phosphatase, dehydrogenase, urease, amylase, invertase, and cellulase were observed in the panchakavya-treated soil.

Effect of dehydrogenase, phosphatase and urease activity in cotton soil after applying thiamethoxam as seed treatment

Soil enzymes are indicators of microbial activities in soil and are often considered as an indicator of soil health and fertility. They are very sensitive to the agricultural practices, pH of the soil, nutrients, inhibitors and weather conditions. To understand the effect of an insecticide, thiamethoxam, on different soil enzyme activities, the experiments were conducted at cotton experimental fields of Punjab Agricultural University, Ludhiana. The results here were presented to understand the impact of thiamethoxam on soil enzyme activities. Thiamethoxam was applied as seed treatment to control the pest. Soil from three localities, i.e. soil in which seed was treated with recommended dose at 2.1 g a.i. kg(-1), soil in which seed was treated with four times recommended dose at 8.4 g a.i. kg(-1) and from the control field, were tested for different enzyme activities. Phosphatase and dehydrogenase activities were high in control soil in comparison to control soil while no effect of this insecticide on urease activity. Thiamethoxam had inhibitory effects on dehydrogenase and phosphatase activities. Therefore, it can be attributed that agricultural practices, weather conditions and use of thiamethoxam might be responsible for the different level of enzyme activities in soil.

Influence of insecticides flubendiamide and spinosad on biological activities in tropical black and red clay soils

A laboratory experiment has been conducted to investigate the ecological toxicity of flubendiamide and spinosad at their recommended field rates and higher rates (1.0, 2.5, 5.0, 7.5, 10.0 kg ha⁻¹) on cellulase, invertase and amylase in black and red clay soils after 10, 20, 30 and 40-day exposure under controlled conditions in groundnut (Arachis hypogaea L.) soils of Anantapur District, Andhra Pradesh, India. Flubendiamide and spinosad were stimulatory to the activities of cellulase, invertase and amylase at lower concentrations at 10-day interval. The striking stimulation in soil enzyme activities noticed at 2.5 kg ha⁻¹, persists for 20 days in both soils. Overall, the higher concentrations (5.0–10.0 kg ha⁻¹) of flubendiamide, and spinosad were toxic or innocuous to cellulase, invertase and amylase activities, respectively. The results of the present study thus, clearly, indicate that application of the insecticides in cultivation of groundnut, at field application rates improved the activities of cellulase, invertase and amylase in soils.

Structure-toxicity relationship of chloroacetanilide herbicides: relative impact on soil microorganisms

The research was carried out to ascertain the effect of three chloroacetanilide herbicides, alachlor, butachlor and pretilachlor on soil microbial biomass growth and activity. Laboratory experiments were performed in a silty clay loam soil to relate changes of soil enzymatic activity to the herbicide persistence under laboratory condition up to 42 days at three application rates. The results showed that all the three herbicides caused enhancement of dehydrogenase activity. Higher concentrations of herbicide resulted in enhancement of the enzymatic activity. In addition, a similar trend was observed in β-glucosidase and acid phosphatase activity, although urease activity decreased upon incubation for 42 days as compared with initial soil incubation values. Based on the extent of impact for dehydrogenase activity in soil, the order was pretilachlor>alachlor>butachlor; whereas in case of urease activity, the order changed to pretilachlor>butachlor>alachlor. The soil half-lives of alachlor, butachlor and pretilachlor respectively, were 9.3, 12.7 and 7.3 days, which could be accounted for in terms of their respective chemical structures, as well as variable adsorption, degradation, differential effects of the agents on soil microbes. Soil management practices and the differing physicochemical properties of the herbicides may contribute to their rates of decay in soil.

Impact of Fungicides Chlorothalonil and Propiconazole on Microbial Activities in Groundnut (Arachis hypogaea L.) Soils

Introduction of agrochemicals (fungicides) into soil may have lasting effects on soil microbial activities and thus affect soil health. In order to determine the changes in microbial activity in a black clay and red sandy loam soils of groundnut (Arachis hypogaea L.) cultivated fields, a case study was conducted with propiconazole and chlorothalonil to evaluate its effects on soil enzymes (cellulase and invertase) throughout 40 days of incubation under laboratory conditions with different concentrations (1.0, 2.5, 5.0, 7.5, and 10.0 kg ha⁻¹). Individual application of the two fungicides at 1.0, 2.5, and 5.0 kg ha⁻¹ to the soil distinctly enhanced the activities of cellulase and invertase but at higher concentrations of 7.5 and 10 kg ha⁻¹ was toxic or innocuous to both cellulase and invertase activities. In soil samples receiving 2.5–5.0 kg ha⁻¹ of the fungicides, the accumulation of reducing sugar was pronounced more at 20 days, and the activity of the cellulase and invertase was drastically decreased with increasing period of incubation up to 30 and 40 days.

Interaction effects of insecticides on microbial populations and dehydrogenase activity in a black clay soil

Three insecticides, monocrotophos, quinalphos, and cypermethrin, were applied at 0, 5, 10, and 25 microg g(-1) either singly or in combination to a black clay soil to investigate their effects on the soil microflora and dehydrogenase activity. All three insecticides significantly enhanced the proliferation of bacteria and fungi and the soil dehydrogenase activity even at the highest level of 25 microg g(-1). Monocrotophos or quinalphos in combination with cypermethrin at tested levels interacted significantly to yield additive, synergistic, and antagonistic responses toward bacteria and fungi and dehydrogenase activity in soil. Antagonistic interactions were more pronounced toward soil microflora and dehydrogenase activity when the two (monocrotophos or quinalphos + cypermethrin) insecticides were present together in the soil at highest level (25 + 25 microg g(-1)), whereas synergistic or additive responses occurred at lower level with the same combination of insecticides in soil.