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Assam Agricultural University, Jorhat
Assam Agricultural University is the first institution of its kind in the whole of North-Eastern Region of India. The main goal of this institution is to produce globally competitive human resources in farm sectorand to carry out research in both conventional and frontier areas for production optimization as well as to disseminate the generated technologies as public good for benefitting the food growers/produces and traders involved in the sector while emphasizing on sustainability, equity and overall food security at household level.
Genesis of AAU -
The embryo of the agricultural research in the state of Assam was formed as early as 1897 with the establishment of the Upper Shillong Experimental Farm (now in Meghalaya) just after about a decade of creation of the agricultural department in 1882. However, the seeds of agricultural research in today’s Assam were sown in the dawn of the twentieth century with the establishment of two Rice Experimental Stations, one at Karimganj in Barak valley in 1913 and the other at Titabor in Brahmaputra valley in 1923. Subsequent to these research stations, a number of research stations were established to conduct research on important crops, more specifically, jute, pulses, oilseeds etc. The Assam Agricultural University was established on April 1, 1969 under The Assam Agricultural University Act, 1968’ with the mandate of imparting farm education, conduct research in agriculture and allied sciences and to effectively disseminate technologies so generated. Before establishment of the University, there were altogether 17 research schemes/projects in the state under the Department of Agriculture. By July 1973, all the research projects and 10 experimental farms were transferred by the Government of Assam to the AAU which already inherited the College of Agriculture and its farm at Barbheta, Jorhat and College of Veterinary Sciences at Khanapara, Guwahati.
Subsequently, College of Community Science at Jorhat (1969), College of Fisheries at Raha (1988), Biswanath College of Agriculture at Biswanath Chariali (1988) and Lakhimpur College of Veterinary Science at Joyhing, North Lakhimpur (1988) were established. Presently, the University has three more colleges under its jurisdiction, viz., Sarat Chandra Singha College of Agriculture, Chapar, College of Horticulture, Nalbari & College of Sericulture, Titabar. Similarly, few more regional research stations at Shillongani, Diphu, Gossaigaon, Lakhimpur; and commodity research stations at Kahikuchi, Buralikson, Tinsukia, Kharua, Burnihat and Mandira were added to generate location and crop specific agricultural production packages.
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ThesisItem Open Access EFFECT OF CRUDE OIL SPILLAGE ON SOIL PHYSICAL PROPERTIES AND RECLAMATION OF THE AFFECTED SOILS(AAU, Jorhat, 2017-07) Goswami, Kasturi; Kulendra Nath DasThe release of crude oil into the environment by oil spillage is receiving worldwide attention due to the potential risk posed to the environment. Crude oil spillage is a regular phenomena in the oil drilling sites and the areas through which oil transportation pipelines carries the crude oil either to the oil collecting station (OCS) or to the oil refineries. Due to raining and flooding the spilled oil and oily sludge spread to the nearby cultivated field causing soil pollution and heavy reduction in the crop yield. Therefore, the present investigation was aimed to study the effect of crude oil spillage on soil physical properties and the influence of organic amendments as remediants in reclaiming the affected soils. Five soil samples in triplicates at an interval of 50m from three directions (E,W& S) from the spilled areas and one samples each from adjacent unpolluted areas were collected from two oil fields of Assam i.e. MFN, Moran, Dibrugarh and HYR, Kathalguri, Duliajan, Tinsukia where oil exploration activities are conducted by Oil India Limited (OIL). The samples were characterized for their physico-chemical properties. A pot experiment was conducted in the Department of Soil Science, AAU, Jorhat, Assam with unpolluted soils from the above oil fields under factorial set of treatments having five levels of crude oil pollution (0, 60, 90, 120 and 150 ml) and seven amendment treatments viz. poultry manure (PM), farm yard manure (FYM), vermicompost (VC), poultry manure + farm yard manure (PM + FYM), poultry manure + vermicompost (PM + VC) and farm yard manure + vermicompost (FYM+VC) with one control. After 30 days of crude oil addition, the soils were treated for another 15 days with the amendments, and then rice seedling of var. Ranjit was transplanted and grown upto the harvest of crop for two consecutive years i.e. 2014-15 and 2015-16 repeating treatments in 2nd year. Soil samples were collected before crude oil application, after 30 days of pollution treatment, after 15 days of amendment treatment and after harvest and analyzed for their physico-chemical properties. All agronomical data were recorded after harvest of the crop. The results revealed that the soils of Moran and Duliajan oil fields at 0m distance were highly affected by the oil spillage. The bulk density of soils increased from 1.31 to 1.63 Mg m-3 and 1.25 to 1.62 Mg m-3 in Moran and Duliajan oil field respectively, while decreased the total porosity, water holding capacity and hydraulic conductivity. The pH of the soil remarkably dropped with decrease in distance from 5.40 to 4.91 and 5.45 to 4.92, respectively making the soil strongly acidic in nature whereas the organic carbon content increased from 7.12 to 27.36 g kg-1 in Moran and 7.39 to 26.35 g kg-1 in Duliajan oil field. The available N and P2O5 were low near the spillage point and substantially increased with distance. Conversely, Av-K2O, exchangeable Ca2+ and Mg2+ significantly increased near the spilled point. The mean weight diameter (MWD) was maximum near the spillage point and decreased with increasing distance. The water stable aggregates (WSAs) were found higher in the coarser fraction (> 5mm) in soils of 0m and 50m distance whereas beyond 50m, finer fractions recorded the maximum WSAs. Similar trend was observed in organic carbon content in various fractions of WSAs. The total petroleum hydrocarbon (TPH) was maximum at 0m distance in both Moran (14.48 mg g-1) and Duliajan (11.59 mg g-1) oil fields and was negligible beyond 200m. Water retention capacity of soil was lowest at all the applied pressures in the vicinity of drilling point while the values increased with distance. The results of the pot experiment revealed that addition of pollutant deteriorated the soil physico-chemical properties by increasing bulk density of soils while decreasing porosity and water holding capacity. The soil became more acidic and organic carbon and TPH content of soils increased with increased pollution levels whereas the available N, P2O5, K2O and exchangeable Ca2+ and Mg2+ decreased significantly. The addition of organic amendments considerably improved soil parameters by decreasing soil bulk density and TPH content and increasing pH and available nutrient and exchangeable cations. The PM+VC combination amendment showed better results at all the pollution levels. Increase in pollution levels significantly and adversely affected yield attributing characters more pronouncedly at 150ml of crude oil. Addition of different amendment treatments improved the aforesaid plant characters with significant increase in grain and straw yield. The present investigation reveals crude oil spillage as a major factor of soil quality deterioration in Moran and Duliajan oil fields of Assam and the impact was more pronounced in the vicinity of drilling point adversely affecting all the physico-chemical properties of soil. Addition of different levels of crude oil as pollutant also established unfavourable affect on physical properties of soil such as bulk density, particle density, porosity, water holding capacity etc. along with the chemical properties and nutritional status of the soil. Application of organic amendments in various combinations observed to improve soil physico-chemical properties specially reducing TPH content of the soil. Organic amendments i.e. poultry manure + vermicompost (PM+VC) exhibited its excellent capacity to reduce pollution level implying their potentiality as a promising bioremediant for reclamation of crude oil polluted soils. Further, this combination proved to be superior in maintaining crop yield and soil quality.ThesisItem Open Access GIS-BASED EVALUATION OF WATER QUALITY INDEX OF GROUNDWATER AND IDENTIFICATION OF ARSENIC VULNERABLE ZONE FOR POSSIBLE MITIGATION IN RICE ECOSYSTEM OF NAGAON DISTRICT, ASSAM(AAU, Jorhat, 2017-07) Thakuria, Imdad Hussain; Medhi, B. K.Water Quality Index (WQI), a technique of ranking water quality, is an effective way to assess quality and ensure sustainable safe use of water. The present work is aimed to assess groundwater arsenic along with the status of other parameters, their distributions, establishing relationship and evidently finding low cost less arsenic loading technology in irrigated rice field of Nagaon district of Assam for understanding the suitability of water by calculating the WQIand Geographical Information System (GIS) techniques. Eight hundred and eighty three groundwater samples were collected during post-monsoon, 2014-15 and 2015-16 for comprehensive water quality analysis. The spatial distribution maps of 14 decisive parameters viz., arsenic, pH, electrical conductivity, total dissolved solids, calcium, magnesium, carbonate, bi-carbonate, nitrate, sulphate, fluoride, iron, aluminium and manganese having desirable and undesirable classes based on BIS and WHO standards were prepared using Arc GIS 9.3 software. The results of spatial variability maps to identify vulnerable risk zone of different groundwater quality parameters indicated an increase in the percentages of contamination levels especially for arsenic (40.4% – 99.5%), aluminium (99.8%), iron (89.6) and manganese (73.5%). Total Dissolved Solids, calcium, magnesium, carbonate, bi-carbonate, nitrate sulphate and fluoride were recorded within the desirable limit and considered to be safe. The concentration of Fluoride in certain areas (33 per cent) of the district was found far below the lower threshold limit suggesting the concerned agencies to opt for suitable less fluoride management strategies. The overall Water Quality Index was found to be 96.48 distinguishing the ground water as “GOOD WATER” with a tendency to fall in “POOR WATER” category. Spatial autocorrelation for all the quality parameters were found distributing in three patterns viz. CLUSTER for pH, EC, As, F, Fe, Al, Mn,HCO3; RANDOM for Mg, Ca, CO3, NO3, SO4 and DISPERSED for TDS, and thus paving a way to address these important parameters based on their space and values. Relationship between groundwater as well as soil arsenic content with other quality parameters showed that 39.1% of arsenic in ground water and 10.4% arsenic in soil could be predicted by the above mentioned parameters.In regards to arsenic distribution in irrigated summerrice, a location was identified from groundwater arsenic risk prone area from GIS-aided arsenic map. An in-situ low cost technology using biochars as strong adsorbent was developed from locally available bio-wastes from rice straw and toria stover. A farmers’ friendly easy to use kiln for production of biochars in field condition was fabricated and accepted overwhelmingly by the local farming community. Application of biochars at 1 to 2 percent levels applied at the conveyance channel of 45 meter long and 43 cm width, irrespective of sources, reduced the root, straw and grain arsenic content and thus the technology would be helpful in reducing arsenic entry into food chain through rice without compromising the optimum rice yield.ThesisItem Open Access CULTURABLE ENDOPHYTIC ACTINOBACTERIA: ISOLATION AND CHARACTERIZATION FROM RICE PLANTS(AAU, Jorhat, 2017-10) Devi, Yumnam Bijilaxmi; Nath, DhrubaJyotiIn the present investigation, endophytic actinobacteria were isolated from six different varieties of rice namely Aghoni Bora, Badshabhog, Basundhara, Ranjit, Joha andSolpuna. Samples were collected from 33 sites located at Golaghat and Jorhat districts of Assam. The isolates were assessed for morphological characterization, biochemical characterization and physiological features with special reference to antimicrobial activities against pathogenic fungi as well as bacteria. Finally, eleven selected isolates were subjected to 16S rDNA sequence analysis for establishment of their genotypic position. Altogether 57 isolates were obtained from six varieties of rice in Starch Casein Agar (SCA) and Casein Yeast Extract Glucose Agar (CYGA) medium. Overall, occurrence of actinobacteria colonies were more prominent in roots compared to stems and leaves. Among the six different rice varieties, the frequency of morphologically well recognized actinobacteria colonies were found to be significantly highest in Solpuna in roots (131.00 g-1), stem (117.00 g-1) and leaves (106.00 g-1). Based on distinct colony morphology and prominent growth without contamination on SCA media, 24 isolates were selected for in-vitro plant growth promoting traits. The growth of all isolates was found to be optimum at pH 7.2 and at temperature 300C ranging from 4.78 to 7.94 log cfumL-1 and 5.00 to 8.67 log cfumL-1respectively. Most of the isolates showed positive result for intracellular and extracellular enzymatic activities. 50% of the isolates showed positive result for gelatin liquefaction. All the isolates except AL2 and SL3W could hydrolyze lipid. 70.83% showed positive result for nitrate reduction. All the isolates except AL2 and SR4 showed negative reaction for catalase activity. Except AS1, SL3W and WNPR1, all the isolates illustrated positive urease activity. All the isolates displayed negative result for H2S production except AS1. 62.5% isolates could produce siderophore and all the isolates could produce hydrogen cyanide. The ability of the isolates to solubilize P was recorded after 7 and 14 days of growth. After 7 days of growth, the value ranged from 0.067 to 0.500 µg mL-1 and 0.067 to 0.633 µg mL-1 after 14 days of growth. The isolates showed similar result in IMViC (Indole, Methyl red, VogesProskaur’s and Citrate utilisation), 66.7 % isolates giving positive result for methyl red test.Rare utilization of carbon sources utilization was observed in all the isolates.Twenty two isolates showed antimicrobial activity against at least three pathogenic fungi. Isolate AS1, AL1, ABR1, BRL2, BRL3, BSS1, BSL1, SS1, SS3, SS5, SL1, SL2, SL3W, SL3Y and SL4 showed inhibition against all the four pathogenic fungi viz.Fusarium oxysporum, Rhizoctoniasolani,Curvularialunataand Sclerotiniasclerotiorum. Overall, isolates BSL1 and SL3W showed high inhibition against all the four pathogenic fungi tested.Six isolates out of twelve selectedviz. ABR1, BRL2, BSL1, SL1, SL3W and SL4 showed high inhibition against pathogenic bacteria Xanthomonasoryzae and four isolates ABR1, BRL2, BSL1 and SL1 exhibited inhibition against Erwinia sp. The inhibition zone ranged from 17 to 24 mm against Xanthomonasoryzae and 19 to 30 mm against Erwinia sp. The isolates showing high antimicrobial properties showed antibiotic resistance against few common antibiotics. Taxonomic identity of selected 11 isolates belonged to Streptomyces longispororuber, Nocardiopsissp., Streptomyces rochei, Streptomyces finlayi, Nocardiopsisalba, Streptomyces sp., Streptomyces parvulus and Streptomyces coelicolor. Most common genus was found to be Streptomyces (81.8%).In conclusion, it was established that rice plants of Assam harbors potential endophytic actinobacteria possessing multiple plant growth promoting traits with antimicrobial activities. These isolatescould be potential candidates for inclusion in integrated nutrient management and organic farming as a means of growth promoter as well as plant disease suppressor.ThesisItem Open Access SCREENING AND EVALUATION OF METHANOTROPHIC BACTERIA FROM RICE ECOSYSTEM(AAU, Jorhat, 2017-07) Phukan, Amrita; Baruah, RajenMethane (CH4) is an important greenhouse gas with 25 times more global warming potential than carbon dioxide (CO2). Rainfed/wetland rice fields are one of the major anthropogenic sources of CH4 release to the atmosphere. Therefore, there is utmost need to mitigate the methane menace. Microorganisms especially Methanotrophs play vital role for biological sink of methame through oxidation to CO2. Considering the fact, the present study was undertaken to isolate and screen novel organisms with methane oxidising properties. A total of 28 Methanotrophic bacterial cultures were isolated from 20 different rice rhizosphere samples of Jorhat district. Altogether 11 out of 28 isolates were selected as methanotrophs on the basis of their growth in Nitrate Mineral Salt (NMS) with CH4 as their sole carbon source. The 11 Methanotrophic bacterial cultures were characterized on the basis of cell morphology, carbohydrate utilization and the degree of susceptibility towards the antibiotics to assess variation within the cultures. All the isolates were screened for their methane oxidizing property and other enzyme activities viz., soluble methane monooxygenase (sMMO), particulate methane monooxygenase (pMMO) and nitrate reductase. The results showed the variation among the cultures in enzyme activities, however all the selected cultures showed methane oxidizing property to the tune of 16053.153 ± 1.333 ppm CO2 to 1787.574 ± 0.938 ppm CO2. Nitrate reductase and sMMO activity was also determined quantitatively for all the isolates to screen the efficient cultures. Specific activity of sMMO by different cultures ranged from 685.489 ± 0.494 nmol h-1 mg of protein-1 to 55.712 ± 0.659 nmol h-1 mg of protein-1. The nitrogenase enzyme activity was determined to check the biofertilizer potential of the test cultures by acetylene reduction assay. The amount of acetylene reduced to ethylene by the test isolates ranged from 8.282 ± 0.240 µmole C2H4/ml/hr to 0.015 ± 0.003 µmole C2H4/ml/hr. The bacterial strains recorded varying soil enzyme activities under soil incubation study of 30 days indicating its role in maintaining soil health. Some of the enzyme activities studied were: MBC, Dehydrogenase, Phosphomonoesterase, FDA hydrolysis, arylsulfatase and urease. The test cultures showed variation in these properties. It was observed that methane oxidation and emission highly correlated with some of the enzyme activities. For instance, Dehydrogenase was found to be the most influencing parameter for methane oxidation ( r = 0.887, P =0.001) and emission ( r = -0.611, P =0.001). Similarly, there was a significant positive correlation between sMMO activity and methane oxidation ( r = 0.536, P =0.001) but a negative correlation with methane emission ( r = -0.539, P =0.001). Based on qualitative and quantitative evaluation, the Methanotrophic bacterial cultures were selected for pot culture evaluation taking rice as test crop. The rice seedlings were inoculated with Methanotrophic bacterial cultures and grown for 35 days. The methane flux were recorded at tillering stage using closed acrylic chamber method. Methane flux recorded for different strains along with uninoculated control ranged from 3639.504 ± 2.254 µg CH4/m2/day Soil to 313.202 ± 3.314 µg CH4/m2/day Soil and also plant growth promotion was observed in all inoculated treatments over uninoculated control which was evident from increase in plant height, root length, tiller number, fresh weight and dry weight. Among the test organisms, MB 16 and MB 28 significantly reduced the methane flux over other Methanotrophs. The results further showed that other Methanotrophic cultures also performed better in reducing methane emission when compared with uninoculated control. Inoculation of MB 16 and MB 28 significantly enhanced the plant growth parameters while other Methanotrophs was either at par or higher than uninoculated control in some of the parameters. 16S rRNA gene sequences of seven methanotrophic cultures revealed that they belonged to the group ɣ-proteobacteria and α-proteobacteria representing the genera Methylomonas, Methylomicrobium, Methylosinus, Chryseobacterium and Methylocystis. The resulted sequences of the organisms were deposited in NCBI, GeneBank with accession numbers. These strains possessed the particulate (pmoA) and soluble (mmoX) methane monooxygenase gene as functional marker for detection of methanotrophs.MB 16 identified as Methylosinus sp. (Type II Methanotroph) and MB 28 identified as Methylomicrobium buryaticum (Type I methanotroph) has been considered as efficient methane oxidizing bacteria having biofertilizer and bioremediation potential which could be exploited along with other potent novel Methanotrophs as future microbial inoculants.ThesisItem Open Access EVALUATION OF CRITICAL LIMIT OF ZINC AND RESPONSE OF RICE TO ZINC APPLICATION IN SOILS OF ASSAM(AAU, Jorhat, 2014-07) Goswami Kandali, Gayatri; Barua, N. G.Georeferenced and representative soil samples were collected from 14 districts of Assam for assessment of zinc status of soils. Altogether, 4110 numbers of surface (0-0.15m) soil samples were collected from rice growing fields of fourteen districts randomly at an interval of 2 to 2.5 km. using Global Positioning System. Thirty numbers (30) of surface (0-0.15m) soil samples were collected from rice growing fields at block level from each district randomly at an interval of 2 to 2.5 km. Based on DTPA-Zn content , soils were categorized as low, medium and high. Nutrient index and fertility ratings were determined following the procedure of Bajaj & Ramamoorty (1969). The highest Zn deficiency (32.21 %) was observed in Lakhimpur district and the lowest ( 2.66 %) in Dhemaji district. The lowest nutrient index (NI) of 1.38 in Nalbari district and the highest (1.63) in Dibrugarh district were recorded. Deficiency of zinc as a whole in the state of Assam represented by the fourteen districts was 26.22%. Twenty five georeferenced bulk surface soil samples (0-30 cm) with variable zinc status were collected from rice growing areas of Assam representing the major soil orders viz. Inceptisol, Alfisol and Entisol to find out the critical limit of Zn in rice soils. A pot culture experiment was conducted taking these soils with four levels of zinc viz., 0,2,4 and 6 kg Zn/ha to find out the response of rice (cv. Ranjit) to applied zinc and the critical limit of zinc in soils and crop. Dry matter yield of rice in control pots ranged between 7.5 to 21.5 g/pot with a mean value of 13.71g/pot. The mean dry matter yield increased significantly over control with rates of zinc application. The highest was recorded in 4 kg/ha of applied zinc. Bray’s percent yield ranged from 57.18 to 95.7 and the highest Bray’s percent yield of 95.7 was observed in the soil having DTPA-Zn of 0.4mg/kg and the lowest value of 57.18 was observed in the soil with DTPA-Zn 2.49 mg/kg. Higher zinc concentration corresponds to higher dry matter yield and higher zinc uptake. The bulk soil samples were also extracted by different extractants viz., DTPA, 0.5N HCl, 0.1N HCl, Ammonium Acetate, EDTA- Ammonium Carbonate, and Ammonium Bicarbonate-DTPA( AB-DTPA), 0.04M EDTA and 2M MgCl2 solution to find out a suitable extractant / method for available zinc in soil . DTPA showed the highest correlation with all the plant parameters followed by AB-DTPA, 0.05 N HCl and EDTA- Ammonium Carbonate. The critical limits( Cate & Nelson,1965) of DTPA, 0.5N HCl , 0.1N HCl, Ammonium Acetate, EDTA- Ammonium Carbonate, AB-DTPA, 0.04M EDTA and 2M Mgcl2 in soil were found to be 1.24, 1.25, 4.8, 0.9, 2.8, 1.74, 2.8 and 0.37mg/kg respectively. The critical limit of Zn for rice was 35 ppm based on DTPA method. In order to study the distribution of different forms of zinc in rice soils and their relative importance to zinc nutrition of rice , Zn fractions of bulk soil samples were extracted by adopting the sequential extraction procedure of Murthy(1982).Water soluble and exchangeable Zn(WSEX-Zn) fraction in soils ranged from 0.32 to 1.92 ,Complexed Zn (COMP-Zn) from 1.46 to 4.5 , Amorphous Sesquioxide bound Zn from 1.30 to 6.21,Crystalline Sesquioxide bound Zn ( CBD-Zn) from 0.45 to2.25 and Residual Zn(Res-Zn) from 101.79 to285.28 mg kg-1 with mean values of 0.87, 2.71, 2.92, 1.12 and 186.98 mg kg-1, respectively. WSEX-Zn, COMP-Zn, Amorphous Sesquioxide bound Zn, CBD-Zn and Res-Zn constituted 0.45, 1.57, 1.62, 0.63 and 95.70 % of total Zn of soils. WSEX-Zn , COMP-Zn and Amorphous Sesquioxide bound Zn was positively and significantly correlated with clay, OC and CEC of soils. However, CBD-Zn was significantly negatively correlated with pH (-0.522**) and Res-Zn was positively correlated with organic carbon (0.425*) and clay (0.397*) c ontent of the soils. Multiple regression of physico-chemical properties of soil with different Zn-fractions showed the highest R2 value (0.616) with COMP-Zn. Multiple regression of different Zn fractions with plant parameters showed the highest contribution of WSEX-Zn to Zn concentration (76.78%), Zn-uptake ( 63.03 %) and dry matter yield ( 36.15 %) of rice. Path analysis of different Zn-fractions with Zn-concentration in rice showed the highest direct effect (0.5610) of WSEX-Zn on Zn concentration and indirect effect of COMP-Zn (0.3731) and Amorphous Sesquioxide bound Zn (0.2508) via WSEX-Zn. A field experiment was conducted for two seasons (2011 and 2012) in a Zn deficient field of the Instructional cum Research Farm of Assam Agricultural University, Jorhat, to study the response of sali rice (var- Ranjit) to zinc application with six levels of ZnSO4 (0, 5, 10, 15, 20 ,25 and 30 Kg/ha) which corresponds to 0, 1.05, 2.1, 3.15, 4.2, 5.25, and 6.3 Kg Zn ha-1 in a randomised block design with three replications. Addition of 25 kg ZnSO4 ha-1 showed the highest increase in plant height by 3.46 %, total tillers by 42.05%, effective tillers by 46.65%, filled grains by 26.86%, and thousand grain weight by 4.96% over control. The percentage of chaffy grain was also lower by 24.43% over control. The grain yield varied from 26.4 q/ha to 45.9 q/ha and straw yield ranged from 55.1 q/ha to 66.4 q/ha due to zinc application. The highest grain yield (45.9 q/ha) and straw yield (66.4 q/ha) was recorded in 25 kg ZnSO4 ha-1 which was significantly higher than all other treatments. Grain yield varied from 34.47 to 73.86%, while straw yield varied from 3.62 to 20.51 % over control. Maximum mean zinc uptake of 97.57 and 311.75 g ha-1 in grain and straw was recorded in 25 kg ZnSO4 ha-1, respectively. The residual zinc was found to be lower in the second year compared to the first year in all the treatments. The treatment with 25kg ZnSO4/ha registered maximum net returns (Rs.23,198.7) and the highest benefit:cost ratio (2.43)ThesisItem Open Access Bioremediation of iron toxicity in lowland rice ecosystem of Assam(AAU, 2016) Tamuly, Danish; Das, K. N.Two sets of experiment viz., pot (2012-13) and field (2013-14) was carried out to find bioremediation potential to ameliorate iron toxicity in lowland rice ecosystem of Assam. Rice crop was cultivated in Yoshida medium (hydroponic culture) developed specifically for rice. The experimental set up consisted of 6 boxes containing 60 PVC cut pipes each. Two check cultivars namely Mahsuri (sensitive) and Padumoni (tolerant) were tried along with eight test cultivars namely Ranjit, Moniram, Kushal, Pankaj, Luit, Basundhara, Jaymoti and Bahadur. Two weeks old seedlings from sand cultured nursery beds were transplanted into the PVC pipes fixed with half-split foam plugs in such a way that only root was in direct contact with the Yoshida solution. Liquid paraffin oil (low density) was added to each PVC pipe to maintain a 3 mm layer for checking oxidation process. Three bacterial inoculations viz., Control, PSB5w and PSB25w along with four iron levels, 0, 500, 1000 and 1500 mg Fe L-1 were tried in different combinations. Sampling at maximum tillering stage of crop revealed leaf scoring ranging from 0.0 to 4.9 with a mean of 0.3 to 3.7. The highest mean scoring of 3.7 was observed at 1500 mg Fe L-1, which was followed by 1000, 500 and 0 mg Fe L-1 with 2.9, 1.4 and 0.3 scoring respectively. The least scoring of 1.2 was observed in PSB5w followed by PSB25w (2.0) and PSB0 (3.1) inoculated cultivars. Among the rice cultivars the leaf scoring was in the order Mahsuri (1.4) < Joymoti (1.6) < Moniram (1.7) < Prafulla (1.9) < Podumoni (2.0) < Ranjit (2.2) < Luit (2.2) < Kushal (2.3) < Basundhara (2.4). Increasing levels of iron from 0 to 1500 mg Fe L-1 was found to significantly reduce the yield attributing traits of cultivars viz., root length (8.0 to 7.0 cm) and shoot length (22.4 to 17.6 cm). Similar reduction was also observed with N, P and K content in both leaf and stem i.e. leaf N (2.42-0.97%), stem N (1.55-0.90%), leaf P (0.220-0.041%), stem P (0.271-0.039%), leaf K (0.473-0.069%) and stem K (1.420-0.208%). The Fe content in different plant parts viz., leaf, stem and root was found to significantly increase with increased Fe-level. Mean root Fe-plaque was found to significantly increase from 0.19 (Fe0) to 0.94 (Fe1500) mg Fe g-1 root. PSB x Fe-level had significant effect on agronomic growth traits viz., root length and number of leaves and on N, P and K content in both leaf and stem. Both leaf and stem N content was found to be significantly higher with cultivars inoculated with PSB5w. However, P and K content in both stem and leaf were found to be higher in PSB25w inoculated cultivars. PSB5w inoculated cultivars recorded significantly lower leaf Fe, stem Fe and root Fe than control and PSB25w. Significantly, higher root Fe plaque was found in cultivars inoculated with PSB5w than PSB25w and control. Negative and significant correlation exist between scoring with root length, shoot length, number of leaves, leaf N%, stem N%, leaf P%, stem P%, leaf K% and stem K%. However, positive and significant correlation was observed between scoring with leaf Fe, stem Fe, root Fe and Fe plaque. Subsequent validation of results of pot experiment was carried out in the ICR Farm, AAU, Jorhat. Six rice cultivars viz., Mahsuri, Moniram, Joymoti, Prafulla, Podumoni and Ranjit in increasing order of scoring were selected. Following this, the strain PSB5w which showed least scoring was also selected with the highest iron level of 1500 mg Fe L-1. PSB5w inoculated cultivar showed significantly higher root length (21.50 cm), leaf N (2.20%), leaf P (0.313%), stem P (0.277%) and leaf K (0.804%) than non inoculated cultivars. Except for Moniram, all other cultivars showed significantly lower leaf and stem iron content. Significant difference in grain yield was observed with inoculated (1730.70 kg ha-1) and non-inoculated (1644.30 kg ha-1) cultivars. Relatively higher grain yield was achieved in PSB5w inoculated cultivars Mahsuri (2000 kg ha-1) and Prafulla (1850 kg ha-1) as compared to control. Thus the Bacillus sp. PSB5w with suitable carrier material can be used as a bioremediation tool for chronically Fe-toxic lowland rice ecosystem in Assam. Further, a stress encountering bio-package consisting of seedling root dip treatment in PSB5w especially for rice cultivars Mahsuri and Prafulla may be advocated for Fe toxicity affected low land rice ecosystem from the present investigation.