PG Thesis
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Item Pollution study of Vembanadu lake and wetland rice ecosystem(Department of Soil Science and Agricultural Chemistry, College of Agriculture, Vellayani, 2022-02-28) Nadiya, S A; Sailajakumari, M SThe present investigation entitled ―Pollution study of Vembanadu lake and wetland rice ecosystem‖ was carried out at the College of Agriculture, Vellayani during the period 2019 to 2021 to assess the extent of pollution in Vembanad lake and wetland rice ecosystem. The lake is part of the Vembanad-Kol wetland system, which stretches from Alappuzha in the south to Azheekkode in the north, making it India's longest lake. The lake is fed by five rivers, including the Achenkovil, Manimala, Meenachil, Muvattupuzha and Pampa which are all prominent rivers in central Kerala. Samples of water and sediment from lake as well as soil and field water from paddy fields were collected during post monsoon and summer season. Samples collected from the two representative sites Kumarakom and Thanneermukkom were subjected to physical, chemical and biological analysis. Results of the analytical study of lake water revealed that among the physical properties, turbidity and colour were above the acceptable limit of BIS drinking water quality criteria and did not varied significantly with seasons. Chemical properties of water viz. pH, BOD, COD, NH4-N and Fe were also above the acceptable limit. pH, EC, K, Na, Ca and Mg varied significantly with season. Electrical conductivity and the cationic nutrients were found to be higher in summer than post monsoon season. Trace metals viz. Mn, Cu, Zn, Al, Pb and Cd were not detected in lake water samples in either of the seasons. Total bacteria and coliform count exceeded the acceptable limit of drinking water quality criteria in the study area. Pesticide residues were not detected in the lake water samples. Sample analysis of the sediment revealed that NO3- N recorded a mean value of 28.00 mg kg1 at Kumarakom and 36.17 mg kg1 at Thanneermukkom. Aluminium varied from 342.00-474.00 mg kg1 at Kumarakom while at Thanneermukkom was 348.00- 468.00 mg kg1 . For Pb, mean value of 0.71 mg kg1 and 0.72 mg kg1was obtained at Kumarakom and Thanneermukkom respectively. Seasonal variation was observed for the chemical properties viz. pH, EC, extractable K, Ca, Mg, S, and Mn. Parameters EC, cationic nutrients except Al, trace metals viz. Mn, Cu, Zn and Pb were found to be highest during summer season while pH, organic carbon, NO3- N, NH4-N, P, Al were highest during post monsoon. Cadmium was not detected in sediment samples collected in both the seasons. Pesticide residue analysis of sediment samples revealed the presence of DDT (0.024 mg kg1 ). Soil samples from padashekaram of Kumarakom were slightly acidic while it was moderately acidic at Thanneermukkom. At Kumarakom and Thanneermukkom organic carbon was high, available N and K were medium and low in available P. At both locations, secondary nutrients were sufficient. Among micronutrients, Fe toxicity and deficiency of Cu and Zn were observed. Chemical parameters of soil were significantly influenced by the seasons. Cationic nutrients and EC were high in summer while pH and organic carbon were high in post monsoon season. Pesticide residue analysis of the soil samples revealed the presence of cypermethrin, chlorpyrifos and ethion. Textural class of soil sample ranged from sandy loam to sandy clay loam. In the field water samples from padashekaram, trace element Fe was detected. Among the chemical properties pH, EC, S, K, Na, Ca, Mg varied significantly with season. Pollution study of Vembanad lake revealed that lake water is polluted with respect to most of the biological, physical and chemical properties. Hence it is important to develop water quality monitoring and management strategies for conserving and sustaining the natural resources from environmental pollution and ecological degradation.Item Documentation and predatory potential of spiders in rice ecosystem and impact of insecticides on spiders(Department of Agricultural Entomology, College of Agriculture, Vellayani, 2007) Anis Joseph, R; Premila, K SThe survey conducted to document the spiders in the paddy fields of Thiruvananthapuram district during the Virippu and Mundakan seasons of 2005-’06, brought out sixty five species of spiders, which fall into two major groups, hunters and web builders and belonged to eleven families and seven foraging guilds. The species composition of hunters was more than the web building spiders, although the latter was numerically dominant. The dominant guild was orb web weavers. Araneidae was the family with more species composition, followed by Tetragnathidae and Salticidae. The predominant genus being Tetragnatha, and species, Tetragnatha mandibulata Walckenaer. The other dominant species were Tetragnatha maxillosa Thorell, Argiope anasuja Thorell, Neoscona rumpfi Tikader & Biswas, Telamonia dimidiata Simon, Bianor carli Reimoser, Oxyopes javanus Thorell, Peucetia viridana Stoliczka, Pardosa pseudoannulata Böesenberg & Strand and Thomisus projectus Tikader. Seventeen species of spiders were reported for the first time from the rice fields of Kerala, and it included the three dominant spiders, viz., N. rumpfi, B. carli and T. projectus. Spiders were also observed in the field bunds and border weeds, and from the webs built among plants, in between the plants and on individual leaves. The seasonal occurrence of spiders during the Virippu and Mundakan seasons did not show any remarkable difference. Among the eleven families, six were more populated viz., Tetragnathidae, Araneidae, Salticidae, Lycosidae, Oxyopidae and Thomisidae. The predominant family was Tetragnathidae. The vegetative and reproductive stages of the crop harboured more spiders and the highest population was recorded during the reproductive stage. The crop growth stages had significant influence over the spider population, where as the weather parameters had no correlation. The ten spiders showed a definite preference for the different hoppers, bugs and lepidopterans when evaluated for their prey preference. The spiders A. anasuja, P. viridana, T. dimidiata and T. projectus broadened their preference to the orthopteran and coleopteran pests. The predatory potential of the spiders showed that the spiders which consumed more number of prey insects per day in a mixed diet took comparatively lower numbers when the prey insects were provided individually. A. anasuja was the most potential predator and P. viridana was the spider with highest rate of hyper predation and the most cross predated insect predator was C. lividipennis. The parasitoids were not consumed by the spiders. The topical application of chemicals recorded higher mortality of spiders than when released on the treated plants. Among the chemicals, imidacloprid 0.005 per cent proved to be safer and triazophos 0.05 per cent more toxic. Azadirachtin 0.004 per cent had more toxicity among the neem formulations. In the field, better recolonization of spiders was noticed in the neem products treated plots than the synthetic pesticides, imidacloprid proved to be the safest chemical for the spiders and all the insect natural enemies and was quite promising for the pests. From the results obtained, it can be concluded that pest management will be effectively executed in the field by these potential predators, which are abundant and had specific adaptations which overpowered the other natural enemies in the rice fields. In a naturally balanced rice ecosystem, in a pesticide free environment, these carnivores can survive and when assembled into groups, they could contribute to significant reductions in pest numbers, which have a positive effect on crop production and is beneficial to farmers. Imidacloprid 0.005 per cent could be utilized for pest control when infestation is severe without harming the spider fauna. Hence, conservation biological control could be practiced along with spider mediated IPM.Item Impact of botanicals on pests and defenders in rice ecosystem(Department of Entomology, College of Agriculture, Vellayani, 2000) Ajaya Kumar, C; Nalina Kumari, TThe magnitude and intensity of insect pest and their defenders at different growth stages of rice were assessed in a survey during the virippu season of 1998, adopting random sampling technique, in three taluks of Thiruvananthapuram district. The survey revealed that the occurrence and distribution of the population of pests and defenders were same in the various locations, where the tolerant variety Jyothi was cultivated. The total population of pests and defenders observed at different growth stages of the crop followed a definite pattern in the three locations. Different concentrations of the leaf extracts of A. indica, and C. infortunatum and nimbecidine were evaluated in the laboratory for their antifeedant and deterrent activity and contact toxicity against important pests of rice and their defenders. Based on the percentage of leaf protection, the plant products tested were superior to control against C. medinalis. The same effect was noticed with N. depunctalis, only with the highest dose of leaf extracts of A. indica and nimbecidine. Seventy five per cent deterrent effect was observed to N. lugens at the highest dose of the plant products. None of the plant products showed any deterrent action against L. acuta or exhibited contact toxicity to L. acuta, C. medinalis. N. depunctalis andN. lugens. Both the defenders tested CL. pseudoannulata and O. nigrofasciatay; were safe with the plant products. 2 Replicated experiment was conducted on rice to evaluate the efficacy of plant products in suppressing the pests as well as in augmenting the defenders under field conditions. The leaf extract of C. infortunatum was found to be efficient in suppressing the population of C. medinalis. The effect was same as that with insecticides. The population of N. depunctalis was reduced by the leaf extracts of A. indica and C. infortunatum as observed in treatment with carbaryl. The suppressing effect observed on N. lugens was same with both the leaf extracts and insecticides, whereas, none of the treatments showed reduction in the population of L. acuta. The total population of the pests in general, showed a varying effect of plant products at different growth stages of the crop. Leaf extracts of C. infortunatum resulted in an immediate suppression of the total population of the pest at 20 DAT, whereas, A. indica gave significant reduction at 40 DAT. The treatments didnot show any effect on the total pest population at 60 DAT. The effect of plant products on spider population revealed that they were found to be safe. The leaf extract of A. indica increased the spider population at 20 DAT and C. infortunatum at 60 DAT, whereas, insecticides showed harmful effect up to three days after application. Adverse effect with plant products on the population of 0. nigrofasciata was not observed in any of the treatments. An increase in the population of the predator was observed with leaf extracts of A. indica at 20 DAT and with C. infortunatum at 40 and 60 DAT. Significant reduction in the population of Agriocnemis spp. was recorded in treatment with leaf extract of C. infortunatum, whereas, significantly higher population was observed in treatment with leaf extract of A. indica. The population of M crocea was reduced due to the application of plant products and the effect was retained up to three days after application. 3 The influence of plant products on the total population of defenders has clearly indicated that the leaf extracts of A. indica and C. infortunatum were safe to the defenders. Based on the P:D ratio, these products were found to have the best effect in augmenting the population of defenders and suppressing the population of pests. Significant differences in the grain and straw yield was not recorded either in treatments with plant products or with insecticides when compared with control. Overall assessment of the results obtained revealed that A. indica and C. infortunatum can be effectively and safely used for the management of important pests of rice with out much adverse effect on non target organisms in the rice ecosystem. Just like A. indica, C. infortunatum could also be utilised for developing effective plant protection chemicals for replacing undesirable synthetic insecticides in integrated pest management.