Effect of pendimethalin and quizalofop on N2-fixing bacteria in relation to availability of nitrogen in a Typic Haplustept soil of West Bengal, India

The effects of the "Stomp" herbicide application on the microbial prevalence in the soil

Agricultural production has benefited a lot from herbicides; however, the use of herbicides caused many environmental problems. Herbicide application can affect the biodiversity of an ecosystem by killing non-target organisms. Microorganisms in the soil are important factors for plant growth; they represent the biological factor of soil fertility. Herbicides can have a beneficial effect on the development of some microorganisms and a negative on others, leading to depletion of microbial diversity in soil. The objective of this work is to determine microbial activity in the soil and to isolate herbicide-resistant bacteria after the use of the "Stomp" herbicide. Agar plate method was used for the determination of microbial prevalence in the soil. The results showed an increase in the total number of bacteria, ammonifiers, fungi, and actinomycetes. Nine isolates, mostly Gram-positive spore-forming rods, showed an ability to grow in the mineral salt medium with different concentrations of "Stomp" herbicide. Isolates G1/1 and G1/2, showed high level of tolerance at the initial pendimethalin concentration of 25 mg/l. Those isolates have the potential to be used to decontaminate herbicide affected ecosystems.

Residue Behavior and Risk Assessment of Rimsulfuron and Quizalofop-P-ethyl in Potato Under Field Conditions

A method for simultaneous quantitation of rimsulfuron, quizalofop-P-ethyl and quizalofop-P in potato plant, soil and potato tuber samples was established. The mean recoveries of rimsulfuron, quizalofop-P-ethyl and quizalofop-P in different matrices spiked with them were 81.4%-101.1%, 76.1%-99.0% and 77.4%-106.4% with relative standard deviations (RSDs) of 2.7%-13.3%, 0.9%-5.5%, 1.7%-11.3%, respectively. The open-field trials in China were conducted in potato cultivation system of Changchun and Jinan. The results indicated that the half-lives of rimsulfuron and quizalofop-P-ethyl were 0.04-13.1 days. The residues of quizalofop-P during the harvest time in Jinan soil were < 0.01-0.044 mg kg^-1, while there was no residue of target herbicides detected in all other samples. The risk assessment results demonstrated that the risk quotients (RQs) of rimsulfuron and quizalofop-P-ethyl were 7.857 × 10^-5 and 8.730 × 10^-3, respectively, which exhibited an acceptable dietary risk to Chinese consumers.

The fungicide "fluopyram" promotes pepper growth by increasing the abundance of P-solubilizing and N-fixing bacteria

Fluopyram, as a reasonably good fungicide and nematicide, is widely used to control agricultural pests worldwide. However, its effects on soil microbial communities and plant growth remain controversial. Therefore, in this study, we investigated the effects of three concentrations (0.5, 1.5, and 5.0 mg/kg) of the fluopyram (Lufuda 41.7% a.i., suspension concentrate, SC) on the pepper rhizosphere microorganisms and pepper seedlings growth in a plant growth room. Moreover, we also investigated the dissipation of fluopyram in the soil, pepper roots, and leaves across a time interval of 45 days. The results showed that fluopyram application increased the number of pepper rhizosphere phosphate (P)-solubilizing bacteria, the abundance of nitrogen (N)-fixing nifH genes, and the pepper seedling growth. The results of terminal restriction fragment length polymorphism (T-RFLP) analysis demonstrated that fluopyram did not alter rhizosphere bacterial community structure and diversity. However, fluopyram did increase the relative abundances of 138 bp and 400 bp T-RFs closely representing Bacillus and Rhizobium genera that were known as efficient plant growth promoting bacteria with P-solubilization and N-fixation properties. Corresponding to the increase of plant growth and beneficial microbes, the half-lives of fluopyram in soil and plant tissues also decreased that nevertheless suggested the role of plant-microbe interactions in the faster removal of fluopyram after application. Our results suggest that short-lived and easily degradable pesticides may have less toxicological effects on soil health while their judicious use may reshape plant-microbe interactions in favor of the plant growth.

Influence of imazethapyr and quizalofop-p-ethyl application on microbial biomass and enzymatic activity in peanut grown soil

A field experiment was conducted to examine the degradation and impact of two post-emergence herbicides (imazethapyr and quizalofop-p-ethyl) on soil ecosystems at a half recommended rate (HRE), recommended rate (RE), and double recommended rate (DRE) during kharif peanut cultivation. Herbicides were innocuous to soil microbial activity at HRE, however, showed some significant influences at RE and DRE, and exerted temporary toxic effects on microbial biomass carbon and fluorescein diacetate hydrolyzing activity. Dehydrogenase activity also declined for a shorter period except imazethapyr application at DRE. Acid phosphatase activity was inhibited whereas alkaline phosphatase activity fluctuated between promotion and inhibition, but promotion was predominant suggesting a direct role of alkaline soil environment. Soil NH₄⁺ and NO₃^- nitrogen were increased by the herbicides at initial (after 7 days) and last phases (after 30 days), respectively. After an early period of inhibition, urease activity returned to the control level after 30 days. Dissipation of imazethapyr residues fitted best to bi-exponential order rate kinetics at DRE and RE, whereas it followed first-order rate kinetics at HRE. The residues of quizalofop-p-ethyl were found only up to 1 day after application suggesting its rapid conversion to active acid metabolites. Both the herbicides had transient harmful effects on most of the soil microbiological parameters.

Effect of Pre-emergence Herbicides on Microbial Biomass and Biochemical Processes in a Typic Fluvaquent Soil Amended with Farm Yard Manure

Application of thiobencarb, pendimethalin and pretilachlor at rates of 7.5, 10.0 and 2.5 kg a.i. ha(-1), respectively, under laboratory conditions, significantly increased microbial biomass C, N and P, resulting in greater availability of C, N and P in soil amended with farm yard manure. Application of thiobencarb highly induced microbial biomass C (46.3 %) and N (40.6 %), while pretilachlor and thiobencarb augmented microbial biomass P to the extent of 14.9 % and 14.1 %, respectively. Application of pendimethalin retained the highest amount of total N (19.9 %), soluble NO3 (-) (56 %) and available P (69.5 %) in soil. A similar trend was recorded with thiobencarb for oxidizable organic C (18.1 %) and with pretilachlor for exchangeable NH4 (+) (65.8 %). At the end of the experiment, the highest stimulation of bacteria was recorded with thiobencarb (29.6 %), while pretilachlor harboured the maximum number of actinomycetes (37.2 %) and fungi (40 %) in soil compared to the untreated control.

Non-symbiotic N2-fixation and phosphate-solubility in Gangetic alluvial soil as influenced by pre-emergence herbicide residues

An experiment has been conducted under laboratory conditions to investigate the effect of two pre-emergence herbicides viz., thiobencarb (at 1.5 and 4.5 kg a.i. ha(-1)) and pretilachlor (at 0.5 and 1.5 kg a.i. ha(-1)), on the changes of growth and activities of aerobic non-symbiotic N2-fixing bacteria and phosphate-solubilizing microorganisms in relation to availability of mineral nitrogen and soluble phosphorus in the Gangetic alluvial soil (Typic Haplustept) of West Bengal, India. Application of herbicides, in general, significantly increased growth and activities of microorganisms, resulting in greater release of available nitrogen and soluble phosphorus in soil; and the stimulation was more pronounced when the herbicides were applied at their lower concentrations (recommended field application rates), more so with thiobencarb, as compared to pretilachlor. As compared to untreated control, application of thiobencarb at lower concentration increased the proliferation of aerobic non-symbiotic N2-fixing bacteria, phosphate-solubilizing microorganisms and non-symbiotic N2-fixing capacity of soil to the extent of 54.0, 44.6 and 31.7%, respectively; and accumulated the highest amount of available nitrogen (37.8%) and phosphorus (54.5%) in soil, while pretilachlor at field application rate highly induced (37.2%) phosphate-solubilizing capacity of soil. At higher concentration, pretilachlor was superior to thiobencarb in augmenting the growth and activities of phosphate-solubilizers. The results of the present study also indicated that gradual increase in concentration of the herbicides over their recommended field application rates was not much conducive for growth and activities of microorganisms, and subsequent release of nutrients in soil.

Residual effect of pre-emergence herbicides on microbial activities in relation to mineralization of C, N and P in the Gangetic alluvial soil of West Bengal, India

An experiment has been conducted under laboratory conditions to investigate the residual effect of three pre-emergence herbicides (thiobencarb, pendimethalin and pretilachlor) at fivefold field application rates (7.5, 10.0 and 2.5 kg a.i. ha(-1), respectively), on the changes of microbial activities and some biochemical processes in the Gangetic alluvial soil of West Bengal. Application of herbicides in general significantly increased microbial biomass resulting in greater mineralization of C, N and P in soil. The highest stimulation of microbial biomass C was recorded with thiobencarb (24.4%) followed by pendimethalin (23.4%). Microbial biomass N was highly induced under pretilachlor (54.5%) and thiobencarb (52.7%), while the stimulation of microbial biomass P was at par in the herbicide-treated soils. Compared to untreated control, the highest amount of organic C was retained with thiobencarb followed by pendimethalin. A similar trend was recorded with thiobencarb for total N, while pendimethalin induced exchangeable NH4 (+) and soluble NO3 (-) to the highest extent (42.2 and 34.5%, respectively). Regarding the availability of P in soil, pretilachlor manifested greater stimulation (33.1%) than thiobencarb (21.6%) and pendimethalin (11.4%). As compared to untreated control, thiobencarb harboured maximum number of bacteria (107.9%), while pretilachlor exerted the highest stimulations towards the proliferations of actinomycetes (132.6%) and fungi (149.5%) in soil.

Effect of thiobencarb and pretilachlor on microorganisms in relation to mineralization of C and N in the Gangetic alluvial soil of West Bengal

An experiment was conducted under laboratory conditions to investigate the effect of two pre-emergence herbicides, viz., thiobencarb (at 1.5 and 4.5 kg active ingredient (a.i.) ha(-1)) and pretilachlor (at 0.5 and 1.5 kg a.i. ha(-1)), on the growth and multiplication of some microorganisms (bacteria, actinomycetes and fungi) in relation to transformations and availability of C and N in the Gangetic alluvial soil (Typic Haplustept) of West Bengal, India. Application of both the herbicides, in general, significantly increased microbial biomass, resulting in greater retention, mineralization and availability of oxidizable organic C and N in soil, and the stimulations were more pronounced when the herbicides were applied at their lower concentrations (recommended field application rates), more so with thiobencarb, as compared to pretilachlor. Compared to untreated control soil, the application of thiobencarb at lower concentration increased the proliferation of total bacteria, actinomycetes and fungi by 57.3, 36.6 and 55.2%, respectively, and released the highest amount (40.2%) of soluble NO₃(-) in soil, while pretilachlor at field application rate induced the growth and multiplication of bacteria and fungi by 58.3 and 17.6%, respectively. Irrespective of the concentrations, the stimulations were at par for both the herbicides towards the retention of oxidizable organic C, total N and exchangeable NH₄(+) in soil.

Effect of combined application of systemic herbicides on microbial activities in north bengal alluvial soil

An experiment was conducted under laboratory conditions to investigate the effect of combined application of three systemic herbicides, viz., fenoxaprop, pendimethalin and paraquat at 50 g, 1.0 kg and 1.0 kg a.i. ha(-1), respectively, on the changes of microbial biomass C, N and P in relation to transformations and availability of some plant nutrients in an alluvial soil (Typic Orchraqualf) of West Bengal, India. Application of the herbicides, in general, significantly increased microbial biomass C, N and P, resulting in greater availability of C, N and P in soil. The microbial biomass C was highly induced (28.4 %) when fenoxaprop was applied with pendimethalin, while fenoxaprop along with paraquat exerted maximum stimulation towards microbial biomass N (19.9 %) and biomass P (16.2 %). Application of fenoxaprop along with pendimethalin retained the highest amount of organic C (17.4 %), exchangeable NH4(+) (29 %) and available P (19.6 %), while fenoxaprop with paraquat augmented total N and soluble NO3(-) by 21.4 % and 25.2 %, respectively in soil.

Effect of systemic herbicides on microbial biomass in relation to availability of some plant nutrients in an alluvial soil of West Bengal

An experiment was conducted under laboratory conditions to investigate the effect of three herbicides, viz., fenoxaprop, pendimethalin and paraquat, at their recommended field application rates (50 g, 1.0 kg and 1.0 kg a.i. ha⁻¹, respectively), on the changes of microbial biomass C, N and P in relation to transformations and availability of plant nutrients in an alluvial soil (Typic Orchraqualf) from West Bengal, India. Application of herbicides, in general, significantly increased the microbial biomass C, N and P, resulting in greater availability of these plant nutrients in soil. The microbial biomass C was highly increased due to application of fenoxaprop (39.8%) followed by paraquat (28.2%). Application of pendimethalin led to the maximum stimulation of microbial biomass N (37.1%), while microbial biomass P was increased by 15.2% following the incorporation of paraquat into the soil. Compared to untreated control soil, the soil retained the highest amount of organic C (19.8%) when it was treated with pendimethalin. A similar trend was recorded with fenoxaprop for total N (19.6%) and exchangeable NH₄⁺ (21.3%) in soil. The stimulation of soluble NO₃⁻ was highest under fenoxaprop (22.3%) followed by paraquat (20.7%). Regarding the availability of P in soil, paraquat manifested greater stimulation (17.8%) than fenoxaprop (15.4%) or pendimethalin (13.1%). Application of paraquat also gave the highest amount of total P (17.8%) in the soil solution.