Effect of selected insecticides on soil microbial load in rice ecosystem

Transcription

1 Effect of selected insecticides on soil microbial load in rice ecosystem A. Rajesh 1*, T. Manoharan 1, S. Kuttalam 1 and K. Ilamurugu 2 1 Department of Agricultural Entomology, Tamil Nadu Agricultural University, Coimbatore, T. N., India 4 Department of Agricultural Microbiology, Tamil Nadu Agricultural University, Coimbatore, T. N., India * rajesh68.ag@gmail.com ABSTRACT Field and laboratory experiments were conducted to study the effect of carbosulfan 25 EC (NS) and chlorpyrifos 20 EC on the soil microbial load in the rice fields during Application of carbosulfan 25 EC (NS) at the test doses (150, 200, 250 and 300 g a.i ha -1 ) and chlorpyrifos 20 EC at 250 and 375 g a.i ha -1 in rice did not show any noticeable adverse effects on soil bacterial and fungal count in rice field. Carbosulfan 25 EC (NS) at 300 g a.i ha -1 have moderate toxic effect on the population of actinomycetes in rice field during the early stages, but this effect was nullified at the later stages of the crop. Chlorpyrifos 20 EC at 250 and 375 g a.i ha -1 and carbosulfan 25 EC (NS) at lower doses, 150, 200 and 250 g a.i ha -1 did not show any adverse effects on the soil actinomycetes count in rice field. Carbosulfan at recommended dose 250 g a.i ha -1 is relatively safer than the higher dose 300 g a.i ha -1 in terms of toxicity to the soil bacterial, fungal and actinomycetes count in rice field. KEY WORDS: Carbosulfan, chlorpyrifos, rice ecosystem, soil microbes INTRODUCTION Pesticides are extensively used in agriculture as a part of pest control strategies. Today the world is much concerned about the harmful effects of pesticide residues and their impact on the non-target environment due to indiscriminate usage in agriculture. The amount of applied pesticides reaching the target organism is about 0.1% while the remaining bulk contaminates the soil environment (Carriger et al., 2006). With the growing use of pesticides in contemporary agriculture, the issue of the impact of these chemicals on the composition of soil microorganisms and the processes they direct has received more attention (Baxter and Cummings, 2008). Pesticides may harm the indigenous microorganisms, disturb soil ecosystem, and thus, may affect human health by entering in the food chain. Researchers have already described the adverse impacts of pesticides on soil microbial diversity and activities (Wang et al., 2006). Studies conducted by Duah-Yentumi and Johnson, (1986) showed that repeated applications carbofuran did not show any detectable detrimental effects on soil microbial biomass. Dileep, (2001) found that, application of quinalphos 25 EC and chlorpyriphos 25 EC both as seed treatment and foliar spray in ground nut have no adverse effects on soil bacterial and fungal population, but have temporary toxic effects 359

2 on actinomycetes population which were nullified at the end of the crop season. An array of insecticides is being used for the control of various pests of rice. The right choice of chemical pesticide in pest control is not governed by its toxicity alone, but depends on their safety to natural enemies in the ecosystem and the environment too. Hence, evaluation of a pesticide includes not only the bioefficacy but also its impact on resistance, residues, biodiversity and safety to natural enemies. In the event of change in source material of carbosulfan 25EC, it is mandatory to test its impact on the non target environment along with its bioefficacy, phytotoxicity, residues as per the guidelines of Central Insecticides Board (CIB). The present investigation was under taken to study the effect of carbosulfan 25 EC New Source (NS) on soil microbial load in rice field along with chlorpyrifos 20 EC as standard check. MATERIALS AND METHODS Two field experiments were conducted at Paddy Breeding Station (PBS), TNAU, Coimbatore to study the effect of carbosulfan on soil microbial population in rice field. The experiments were laid out using Randomized Block Design (RBD) with the varietal line CB , one during August November 2012 and another during December 2012 to March 2013, replicated thrice, in plots of size 40 m 2. The treatments evaluated were as follows. Treatment No. Treatment Dose (g a.i. ha -1 ) T 1 Carbosulfan 25 EC (NS) 150 T 2 Carbosulfan 25 EC (NS) 200 T 3 Carbosulfan 25 EC (NS) 250 T 4 Carbosulfan 25 EC (NS) 300 T 5 Carbosulfan 25 EC (ES) 250 T 6 Chlorpyrifos 20 EC 250 T 7 Chlorpyrifos 20 EC 375 T 8 Untreated Control - In both trials, spraying was done with 500 litres of spray fluid per hectare using battery operated knapsack sprayer. Soil samples of different treatments were collected from the rhizosphere region of rice plant at a depth of 10cm, from five randomly selected spots of the each plot (40m 2 ). Samples were collected at before spraying and at 15 and 30 DAA (Days after application) for enumeration of total bacteria, fungi and actinomycetes. Enumeration was done by employing serial dilution and plating technique. One gram of soil sample was taken and 10 fold dilution series were prepared up to One ml of aliquot from the respective dilutions for each organism was taken for plating with appropriate medium and replicated thrice. Bacterial population Enumeration of bacteria was carried out with Nutrient Agar medium (Allen, 1953) using drop plate technique (Miles et al., 1938). The nutrient agar medium was 360

3 poured into the sterilized Petri plates and allowed to solidify and sufficiently dry so as to absorb a 10μl drop. Plates were divided into equal sectors and labelled for respective treatments. In each sector, 10μl of 10-3 dilution was dropped onto the surface of the agar without touching the surface of the agar, using micropipette and the drop was allowed to spread naturally for about minutes. The plates were left upright to dry before inversion and then incubated at 37 C for hours. Each sector was observed for growth of colonies over the area of the drop. Discrete colonies were counted and the result was expressed as colony forming units (cfu) g -1 dry weight of soil. Fungal population Enumeration of fungi was carried out using Martin s Rose Bengal Agar medium (Martin, 1950). Streptomycin solution was added to the molten medium after cooling. One ml of aliquot was taken from 10-3 dilution and dispensed in sterile Petri plates and 15ml of cooled Martin s Rose Bengal Agar medium was added and mixed with inoculum for uniform spreading. The plates were incubated after settling of agar. The fungal colonies were enumerated after 4 days of incubation and expressed as number of cfu g -1 dry weight of soil. Actinomycetes population The actinomycetes population was enumerated using Kenknight s Agar medium (Rangaswami, 1996). One ml of aliquot from 10-2 dilution was taken and dispensed in sterile Petri plates and 15ml of cooled Kenknight s Agar medium was added and mixed with inoculum for uniform spreading. The plates were incubated after 361

4 settling of agar. The actinomycete colonies were enumerated after 7 days of incubation and expressed as number of cfu g -1 weight of soil. dry RESULTS AND DISCUSSION The microbial count was taken at before spraying and at 15 and 30 DAA in the field soil of rice to study the effect of carbosulfan 25 EC (NS) on bacterial, fungal and actinomycetes population in each treatment. The bacterial count in soils before spraying (PTC) were ranging from x 10 3 to x 10 3 cfu g -1 soil and x 10 3 to x 10 3 cfu g -1 soil during first and second season respectively (Tables 1 & 2). At 15 DAA, the bacterial count in soils treated with different test doses of carbosulfan 25 EC (NS) ranges from x 10 3 to x 10 3 cfu g -1 soil and x 10 3 to x 10 3 cfu g -1 soil, whereas the untreated check recorded the population of x 10 3 and x 10 3 cfu g -1 soil during first and second season, respectively. Similar trend was observed at 30 DAA also. The mean values of the bacterial count in all the treatments during first as well as in second season were not significantly different from each other. The untreated check recorded the highest bacterial population at all the stages of observation in both the seasons. In the pre-treatment samples, the fungal count ranged from x 10 3 to x 10 3 cfu g -1 soil and x 10 3 to x 10 3 cfu g -1 soil during first and second season respectively (Tables 1 & 2). At 30 DAA there was a moderate increase in the fungal population in all the treatments that ranged from x 10 3 to x 10 3 cfu g -1 soil and to x 10 3 cfu g -1 soil during first and second season respectively. The mean fungal populations of all the treatments during both the seasons showed that the treatments were not significantly different from each other. The population of actinomycetes was comparatively lower than other microbes and was found to decline at 15 and 30 DAA than the pre-treatment count in all the treatments in both the seasons. At 15 DAA, the actinomycetes count in soils treated with different test doses of carbosulfan 25 EC ranged from 6.00 x 10 2 to 9.17 x 10 2 cfu g -1 soil and 1.33 x 10 2 to 2.14 x 10 2 cfu g -1 soil, whereas the untreated check recorded the population of 9.67 x 10 2 and 3.33 x 10 2 cfu g -1 soil during the first and second season respectively (Table 1 & 2). At 30 DAA, the actinomycetes population ranged from 6.67 x 10 2 to 9.33 x 10 2 cfu g -1 soil and 2.00 x 10 2 to 3.67 x 10 2 cfu g -1 soil during first and second season, respectively and the 362

5 treatments were not significantly different from each other. The present results revealed that, the insecticide treatment did not cause any noticeable adverse effect on bacterial count even at higher dose of carbosulfan 25 EC (NS) i.e, 300g a.i. ha -1 in both the seasons of study. The untreated check recorded comparatively higher bacterial population than the other treatments, but the difference was non-significant in both at 15 and 30 DAA during both the seasons of study. The effect of carbosulfan 25 EC (NS) on the population of fungi followed a similar trend as that of bacterial population. A gradual increase in the fungal count from PTC to 30 DAA was observed in all the treatments during both the seasons of study. Carbosulfan 25 EC 300g a.i. ha -1 had moderate toxic effect on the population of actinomycetes in rice during the early stages. The actinomycetes population was slightly reduced in all the treatments at 15 DAA and thereafter recovered slowly at 30 DAA irrespective of the treatments during both the seasons of study. The results of the present study were in agreement with the findings of Vinod et al. (2012) who found that, there was no significant change in the total viable count of bacterial and fungal populations, after application of carbofuran, phorate, carbosulfan and thiamethoxam in leguminous crops. Similar result was obtained by Singh et al. (2000) who found that, application of quinalphos 25 EC and chlorpyriphos 25 EC both as seed treatment and foliar spray in soyabean had no adverse effects on soil bacterial and fungal population but have moderate toxic effects on actinomycetes population. CONCLUSION Application of carbosulfan 25 EC (NS) and chlorpyrifos 20 EC at the test doses on rice did not show any noticeable adverse effects on soil bacterial and fungal count in rice field, but have moderate toxic effect on the population of actinomycetes in rice field during the early stages. Carbosulfan at recommended dose 250 g a.i ha -1 is relatively safer than the higher dose i.e. 300 g a.i ha -1 in terms of toxicity to the soil microbes in rice field. REFERENCES Allen, O. N Experiments in Soil Bacteriology, Burges Publ. Co., Minneapolis, Minn., U.S.A Baxter, J., and Cummings, S. P The degradation of the herbicide bromoxynil and its impact on bacterial diversity in a top soil. J. Appl. Microbiol, 104: Carriger, J. F., Rand, G. M., Gardinali, P. R., Perry, W. B., Tompkins, M. S., and Fernandez, A. M Pesticides of potential ecological concern in sediment from South Florida Canals: An ecological risk prioritization for aquatic arthropods. Soil Sed.Contam, 15: Duah-Yentumi, S. and Johnson, D.B Changes in soil microflora in response to repeated applications of some pesticides. Soil Biol. Biochem, 18: Dileep, K. S Effect of Insecticide Treatments on the Soil Microbial Population in the Groundnut Fields. Extended Abstracts: Intern. Conf. on Pesticides, Environment, Food Safety. Society of Pesticide Science India, November pp

6 Miles, A. A., Misra, S.S and Irwin, J.O The estimation of the bactericidal power of the blood. J. hygiene, 38 (6): Martin, J.P Use of acid rose bengal and streptomycin in the plate method for estimating soil fungi. Soil Sci, 69: Rangaswami, G Agricultural Microbiology. Asia Publishing House. London.146p. Singh, O.P., Singh, K.G and Nema, K.K Efficacy of some seed dressing and granular insecticides against major insect pests of soyabean. Pestology, 24(1):8-11. Vinod, D., Singh, D., Shukla, A., Shukla, S.and Singh, N Effect of application of different pesticides to leguminous crops on soil microflora of Sidhi district (M.P.). Int. J. Eng. Res. Dev, 3(12):1-3 Wang, M. C., Gong, M., Zang, H. B., Hua, X. M., Yao, J., Pang, Y. J., and Yang, Y. H Effect of methamidophos and urea application on microbial communities in soils as determined by microbial biomass and community level physiological profiles. J. Environ. Sci. Health B, 41: [MS received 24 November 2014; MS accepted 10 February 2015] Disclaimer: Statements, information, scientific names, spellings, inferences, products, style, etc. mentioned in Current Biotica are attributed to the authors and do in no way imply endorsement/concurrence by Current Biotica. Queries related to articles should be directed to authors and not to editorial board

7 Table 1. Effect of carbosulfan 25 EC (NS) and chlorpyrifos 20 EC on soil microbial load of rice field - season I Treatments Dose (g a.i. ha -1 ) Carbosulfan 25EC (NS) 150 Carbosulfan 25EC (NS) 200 Carbosulfan 25EC (NS) 250 Carbosulfan 25EC (NS) 300 Carbosulfan 25EC (ES) 250 Chlorpyrifos 20EC 250 Chlorpyrifos 20EC 375 Untreated check - Microbial count* Bacteria x 10 3 Fungi x 10 3 Actinomycetes x 10 2 PTC 15DAA 30DAA Mean PTC 15DAA 30DAA Mean PTC 15DAA 30DAA Mean (1.66) (1.68) (1.73) a a a a (1.65) a (1.68) a a (1.69) a a (1.74) a a a (1.62) a a (1.69) a (1.66) a (1.79) (1.50) (1.42) (1.48) (1.52) (1.47) (1.50) (1.53) a (1.54) a (1.48) a a (1.50) a a (1.52) a (1.53) a (1.57) a (1.73) a (1.56) a a (1.59) a a a (1.62) a (1.74) (1.12) (1.09) (1.09) (1.00) (1.12) (1.05) (1.09) (1.16) 9.17 a (0.97) 7.67 a (0.82) 6.33 a (0.80) 6.67 a (0.82) 6.00 a (0.78) 6.33 a (0.80) 5.67 a (0.75) 9.67 a (0.95) 9.33 a (0.97) 9.00 a (0.95) 6.67 a (0.80) 8.33 a (0.91) 9.33 a (0.97) 8.67 a (0.92) 9.00 a (0.92) 9.33 a (0.97) CD at P = 0.05% SED *cfu g -1 dry weight of soil; Values represent mean of three replicates. cfu colony forming unit; PTC Pretreatment count; DAA Days after application. In the column, mean values followed by a common letter are not significantly different at P = 0.05 by DMRT. Figures in parenthesis are log 10 transformed values

8 Table 2. Effect of carbosulfan 25 EC (NS) and chlorpyrifos 20 EC on soil microbial load of rice field season II Treatments Dose (g a.i. ha -1 ) Carbosulfan 25EC (NS) 150 Carbosulfan 25EC (NS) 200 Carbosulfan 25EC (NS) 250 Carbosulfan 25EC (NS) 300 Carbosulfan 25EC (ES) 250 Chlorpyrifos 20EC 250 Chlorpyrifos 20EC 375 Untreated check - Microbial count * Bacteria x 10 3 Fungi x 10 3 Actinomycetes x 10 2 PTC 15DAA 30DAA Mean PTC 15DAA 30DAA Mean PTC 15DAA 30DAA Mean (1.63) (1.77) b (1.69) ab ab ab (1.73) b (1.65) ab (1.77) ab a (1.79) ab ab b (1.65) ab ab (1.76) b ab a (1.77) (1.28) (1.29) (1.32) (1.35) (1.28) (1.33) (1.29) (1.34) a (1.54) a a (1.42) a (1.53) a a (1.47) a (1.61) a (1.57) a (1.48) a (1.55) a (1.59) a (1.54) a (1.53) a a (1.48) a (1.61) (0.56) 3.33 (0.49) 2.67 (0.40) 3.33 (0.43) 3.67 (0.58) a (0.10) 2.08 a (0.24) 1.33 a (0.10) 1.67 a (0.20) 2.14 a (0.26) 2.00 a (0.20) 1.67 a (0.16) 3.33 a 2.00 a (0.26) 2.33 a (0.30) 2.33 a (0.36) 3.00 a 3.33 a (0.49) 2.17 a (0.26) 3.00 a 3.67 a (0.55) CD at P = 0.05% SED *cfu g -1 dry weight of soil; Values represent mean of three replicates. cfu colony forming unit; PTC Pretreatment count; DAA Days after application. In the column, mean values followed by a common letter are not significantly different at P = 0.05 by DMRT. Figures in parenthesis are log 10 transformed values