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ThesisItem Open Access SYNTHESIS, CHARACTERIZATION AND RELEASE OF NANO-ENABLED PHOSPHORUS FERTILIZER IN ACID SOILS OF ASSAM(2021) Pachani, Sukanya; Kandali, Gayatri GoswamiThe study on “Synthesis, characterization and release of nano-enabled phosphorus fertilizer in acid soils of Assam” was undertaken during 2019-21with the aim to synthesize and characterize zeolite based nano P fertilizer and to study its release pattern over 90 days of incubation in three different types of soil representing major soil orders of Assam, taking recommended fertilizer dose applicable for maize. Surfactant modification of the zeolite (SMZ) was done by using hexadecyltrimethylammonium bromide (HDTMABr) as surfactant and subsequently, the slow-release fertilizer (SRF) for phosphorus was synthesized by treating the SMZ with potassium dihydrogen orthophosphate to prepare the P-loaded SRF. It was observed from the XRD pattern that the zeolite framework had not undergone major structural change by the addition of HDTMABr and the crystallinity of zeolite remained the same. The surface morphology characterized by SEM, showed that the zeolite was of cubical geometry. The developed zeolite based nano P fertilizer recorded an average particle size of < 100 nm. The specific surface area of nano zeolite fertilizer (modified) was found to be less (90.07 m2/g) as compared to unmodified zeolite (262.72 m2/g). The pore diameter was found to be in the microporous (< 20 nm) range. Maximum adsorption of 7.4% added P was found in nanofertilizer which was 60% higher as compared to unmodified zeolite. The incubation study of P release in different treatments over the different types of soil witnessed marked variations during the entire days of incubation. Although no definite trend was observed in absolute control all throughout the incubation period, the lowest concentration of P was found in 7 days of incubation in all the treatments. In treatment receiving recommended dose of P through SSP, there was a gradual rise in available P concentration, reaching the maximum peak at 32 days of incubation beyond which no further increasing trend was observed. Relatively, the treatment receiving recommended dose of P through nano-fertilizer had a gradual increase of P from 7 days upto 90 days of incubation. A similar trend was also observed in nano treated P fertilizer receiving 2.5 times reduction, 5 times reduction, and 10 times reduction from the recommended dose. However, the concentration of release was lower and found to be in decreasing order as compared to recommended P level applied through nano P. Highest concentration of P at 90 days of incubation was found in recommended P applied through nano-fertilizer in the silty clay loam soil (8.82 mg/kg), which was significantly higher than recommended P applied through SSP (7.54 mg/kg). A significant difference was also noticed between recommended dose of phosphorus applied through nano P (8.82 mg/kg) and treatment receiving 2.5 times reduction of recommended P from nano P (6.38 mg/kg). The same trend of P release was observed in the soil with clay loam and sandy clay loam texture. The differences in clay content between the soils affected the P release pattern which followed the order - Majuli (sandy clay loam) > Jorhat (silty clay loam) > Titabar (clay loam).The first-order kinetic constant was found to increase from 0.096 μg/g/day in recommended dose of P applied through SSP to 0.100 μg/g/day in treatment having a 10 times reduction of recommended P given through nano P in the silty clay loam soil. In the case of second-order kinetics, there was a decrease in rate constant value (-0.015 to - 0.014 g/μg/day) which means an increase in the release of P. The rate constant of parabolic diffusion equation was the highest in treatment receiving recommended dose of P through nano-fertilizer (3.012 μg/g/day) in the silty clay loam soil. This increase in rate constant was found in the clay loam and sandy clay loam soil also which indicated high reactivity of the fertilizer. As observed from the R2 value, the parabolic diffusion equation was found to be the best fit for describing the P release as compared to the other two kinetic models.ThesisItem Open Access SOIL FERTILITY STATUS IN RELATION TO FALLOW CYCLE IN SHIFTING CULTIVATED AREAS OF DIMA HASAO(2021) NUNISA, BAOSRING; Borkakati, KabindraThe present investigation was carried (2019-20) to study the effect of jhum fallow cycle on soil properties in the DIMA HASAO district of Assam. Total of 120 geo-referenced soil samples were collected from short jhum (1-3 yrs.) fallow cycle, medium jhum (4-6 yrs.) fallow cycle, long jhum (7-9 yrs.) fallow cycle and undisturbed soil. The collected soil samples were analyzed for parameters like pH, OC, N, P, K, S, Ca, Mg, CEC, HWS-B, and soil texture. The studied soil samples showed wide variations in texture varying from sandy loam to clay loam. Coarse texture sand was found to be dominant in short jhum and medium jhum while finer particles (silt and clay) were dominant in the long jhum and the undisturbed soil. The Soil pH was found lowest (mean value 4.55) in short jhum and highest (mean value 5.00) in the undisturbed soil. The OC content was minimum at initial short jhum fallow cycle (mean value 0.98%) and maximum was observed in the Undisturbed soil (mean value 1.55%). The CEC of the study area was found highest in undisturbed soil [mean value 8.64 cmol (p+) kg-1] followed by long jhum [mean value 7.98 cmol (p+) kg-1] medium jhum [6.83 cmol (p+) kg-1] and finally by short jhum [mean value 6.53 cmol (p+) kg-1]. The Avl. N content of the study area was found low to medium. Among the jhum fallow cycle Avl. N of short jhum was lowest (mean value 269.30 kg ha-1) followed by medium jhum (mean value285.64 kg ha-1), long jhum (mean value 335.84 kg ha-1) and highest in undisturbed soil (mean value 350.11 kg ha-1). The Avl. P content of the study area was found low to medium. Among the jhum fallow cycle, highest (mean value 12.61 kg ha-1) was observed in long jhum fallow cycle followed by Undisturbed soil (mean value12.03 kg ha-1), medium jhum (mean value 9.55 kg ha-1) and lowest in short jhum (mean value 9.33 kg ha-1). The available K content was found medium to high. Among the jhum soil the lowest mean value was observed in short jhum (169.46 kg ha-1) followed by medium jhum (217.89 kg ha-1), long jhum (244.02 kg ha-1) and the highest in the undisturbed soil (264.40 kg ha-1). The highest content of Avl. S was observed in long jhum fallow cycle (mean value 17.48 kg ha-1) followed by undisturbed soil (mean value 17.32 kg ha-1), medium jhum (mean value 16.09 kg ha-1) and lowest in the short jhum (mean value 13.43 kg ha-1). The highest of Ex. Ca was found in the undisturbed soil [mean value 1.78 cmol (p+) kg-1] followed by long jhum [mean value 1.46 cmol (p+) kg-1], short jhum [mean value 1.40 cmol (p+) kg-1] and lowest in the medium jhum [mean value 1.37 cmol (p+) kg-1]. The highest value of Ex. Mg was found in the undisturbed soil [mean value 1.19 cmol (p+) kg-1] followed by long jhum [mean value 1.09 cmol (p+) kg-1], short jhum [mean value 0.60 cmol (p+) kg-1] and the medium jhum [mean value 0.59 cmol (p+) kg-1]. HWS-B was found highest in undisturbed soil (mean value 0.94mg ha-1) followed by long jhum (mean value 0.81 mg ha-1), medium jhum (mean value 0.70 mg ha-1) and lowest in the short jhum fallow cycle (mean value 0.53 mgha-1). All the soil fertility parameters i.e., N, P, K, S, Ca, Mg, and B exhibited significant positive correlation with pH, OC, CEC, and percent Clay. The highest SQI was observed in the undisturbed soil 24.12 followed by long jhum 23.97, medium jhum 22.03 and lowest in the short jhum 21.46 fallow cycle. Thus, it could be concluded that the minimum jhum fallow cycle should be at least 7 to 9 years.ThesisItem Open Access SOIL BORON FRACTIONS AS INFLUENCED BY SELECTED SOIL PROPERTIES AND CROPPING SYSTEM IN BOKO BLOCK OF KAMRUP (RURAL) DISTRICT OF ASSAM(2021) Baruah, Neelom; Tamuly, DanishThe present study was conducted with the twin objective to assess the influence of basic soil physico-chemical properties and cropping system (CS) on soil boron fractions in Boko Block of Kamrup (Rural) District of Assam. A total of twenty- four (24) geo-referenced surface soil samples (0-15 cm) were collected from across the blocks under each cropping system viz., Rice-Rice, Rice- Fallow, Vegetable-Vegetable and Plantation crops. The soil groups were found to vary in their physico-chemical properties irrespective of cropping system practised. The studied soil samples showed wide variations in texture varying from sandy clay loam (SCl) to clay loam (Cl). The ranges for pH, SOC (%), Av. Nitrogen (kg ha-1), Available P2O5 (Kg ha-1), Available K2O (Kg ha-1), CEC [Cmol (p+) kg-1], EC (dSm-1) ranged between very strongly acidic to strongly acidic (4.7-5.6), medium to high (0.6-1.6 %), Low to Medium (175.6-326.4 kg ha -1), Low to High (5.93- 57.68 kg ha -1), Medium (130.8-276.2 kg ha -1), Low (2.8-9.6 Cmol (p+) kg-1), Normal range (0.01- 0.03 ds m-1) respectively. The selected properties viz., CEC, pH and SOC were chosen based on past research findings to analyze its effect on soil boron fractions. Each of the three parameters were split in two groups: CEC (two groups-2.8-5.8 and 5.9-9.6 C mol(p+) kg-1), pH (two groups- 4.7-5.0 and 5.1-5.6) and SOC (two groups- 0.6-1.0 and 1.1-1.6 %). The data was analyzed using independent sample t-test. It was found that pH and CEC did not significantly affect soil B fraction. However, SOC had a significant effect on soil boron fraction viz., oxide bound and organic bound. In case of CS, majority of the soil properties viz., pH, soil organic carbon, available nitrogen, available phosphorus, cation exchange capacity, sand content (18.1- 49.5%) and silt content (24.1-48.4%) did not differ significantly among the cropping system. However, soil properties like available K2O content, EC, and clay (22.6-38.2%), was found to differ significantly between the cropping system. Cropping system did not significantly affect the various boron fractions in the present study. Significant positive correlation has been observed for soil organic carbon with Oxide bound B (r= 0.834**), Organically bound B (r= 0.541**), Specifically adsorbed B (r= 0.505*) and EC (r= 0.502*). A significant negative correlation has been observed in between sand and silt (r= -0.905 **) as well in sand and clay (r= -0.587**) content among the CS. The available boron (0.56 to 1.69 mg kg-1) and five boron fractions viz., Readily Soluble Boron (0.04-2.41 mg kg-1), Specifically Adsorbed Boron (0.15-1.92 mg kg-1), Oxide Bound Boron (5.18-17.41 mg kg-1), Organically Bound Boron (6.86-20.3 mg kg-1) and Residual Boron (17.73- 36.57 mg kg-1) did not differ significantly between the cropping systems. Results revealed that the relative proportion of various fraction of boron in soils are in the following order i.e. readily soluble B< Specifically adsorbed B < Oxide bound B< Organically bound B < Residual B. The Soil Quality Index for each CS were in the order: Rice-Rice (16.752)> Rice-Fallow (14.645)> Veg-Veg (12.979) > Plantation (12.742). None of the measured parameters were found to be significantly correlated with the yield of crop under the studied cropping system. The study, therefore explores the possibility of soil physico-chemical influence on soil boron fractions owing to cropping system over long period of time. The study reveals the selected soil properties influence on soil B fractions and cropping system being a non- determinant influencing any of the boron fraction studied.ThesisItem Open Access BIORESOURCE POTENTIAL OF FILAMENTOUS CYANOBACTERIA FROM PADDY FIELDS OF ASSAM AND ITS EVALUATION(AAU, Jorhat, 2021) Laishram, Nikita; Baruah, RajenThe present investigation was carried out to evaluate the bioresource potential of filamentous cyanobacteria from rice fields of Assam. Rhizospheric soil samples were collected randomly from Jorhat and Golaghat districts of rice rhizosphere. Altogether 77 cyanobacterial cultures were isolated from 55 numbers of soil samples using BGIIo specific liquid media and 30 cultures thus showed pure colonies. The 30 selected cultures were morphologically characterised on the basis of thallus morphology, trichome, vegetative cell structure, presence or absence of heterocysts and akinetes. The results showed that the cultures were non identical to each other and morphological data and microphotograph thus revealed probable genera belonging to Anabaena, Nostoc, Cylindrospermum and Calothrix. The soil nutrient status and soil enzyme assays as influenced by the various cyanobacteria indicated variation among the soil from where cultures were isolated. The correlation studies revealed a positive correlation with pH, organic C and enzyme activities. Also enzyme activities was seen to be positively correlated with available N, P, K. The nitrogenase enzyme activity was determined using ARA and results revealed a range of 7.70- 26.19 C2H2 nmol ml-1 hr-1 day-1 and culture BGA- 41 showed as the efficient culture. All the isolated cyanobacterial cultures produced significant amount of phytohormones with IAA, GA and cytokinin. Most of the cyanobacterial cultures exhibited positive results for siderophore production, HCN production and proteolytic activity. Quantitative activities of P solubilization and ammonia production was highest shown by BGA- 41. The cyanobacterial isolates were further screened for 16S rRNA gene sequencing for species identification and also to study the phylogenetic relationships among the cultures. The dominant cultures followed as Anabaena > Nostoc > Aliinostoc > Calothrix > Wollea> Cranbergia > Cylindrospermum. 10 efficient cultures based on enzyme and PGP activities were selected for pot experiment to study its efficiency in growth and yield attributing characters in rice crop variety Luit (Ahu). Results indicated that all the inoculated treatments showed better growth and yield as compared to the uninoculated control which was evident from the data obtained on number of tillers, number of panicles, length of panicles, grain yield (g/ hill), straw yield (g) and dry weight of root (g). Grain yield and straw yield of BGA- 41 ranged as 27.67 g/ pot and 12.64 g/ pot respectively. Therefore BGA- 41 was regarded superior to other cyanobacterial cultures which was at par with the recommended fertilizer dose treatment.ThesisItem Open Access ASSESSMENT OF POTASSIUM USE EFFICIENCY IN TRANSPLANTED RICE(2021) Seema Bhagowati; Das, Kulendra NathPotassium (K) the third major essential plant nutrient with diverse roles to play in plant metabolism is required in large amount by crops and is the seventh most abundant element in the earth crust. The total K reserves are generally large in most soils but large portion of soil potassium (90 – 98%) remains chemically bound in the crystal structure of minerals and thus unavailable or slowly available for plant uptake. Based on availability to plants, potassium is categorized into four groups viz., water soluble, exchangeable, non-exchangeable/fixed and lattice K. Potassium supply to crop is a complex phenomenon involving relationships among various K fractions, potassium fixation and release patterns in soil and quantity-intensity relationships. Moreover, the net negative balance for K in current agriculture scenario is 69% which is very high as compared N (19%) and P (12%). This vast difference is partly because of crop removal where 1.5 times more K is removed than N and the application of potassium through fertilizer is considerably lower than that of N or P. Keeping these points in view, a study was carried out on “Assessment of Potassium use efficiency in transplanted rice” in Nagaon district which is famously known as the 'Rice bowl of Assam'. A series of laboratory analysis along with field experiments was carried out to assess the potassium use efficiency in transplanted rice. The soil of the experimental plot was analysed for salient characteristics such as texture including mineralogy of sand, silt and clay, pH, EC, OC, CEC, available NPK contents and various forms of K. An incubation study was conducted upon imposition of ten different treatments for a period of 150 days to know the availability of various forms of potassium in the soils at 20, 40, 60 and 90 days after incubation. After completion of incubation period, soils from various treatments were taken for study the release pattern of step K, constant rate K and cumulative K and fixation of potassium in these soils. Along with the incubation study, a field study was also conducted consecutively for two years with the same ten treatments in rice crop (var. Ranjit) with three replications in RBD design. Post harvested soils were analyzed for various physico-chemical characteristics and different K forms. Crop related data were recorded to study the effect of potassium management on growth and yield of rice. The texture of the soil of the experimental plot was clay loam with very strongly acidic pH (= 4.92). Initial status of SOC (0.91%) was high in upper surface (0-15 cm) and medium (0.65%) in lower surface (15-30cm), available N and P medium and K was low in upper surface and low available N and K and medium P was found in lower surface. X-ray diffraction study clearly indicates that clay fraction of this soil contains minerals like clay mica, mixed-layer minerals, vermiculite, smectite and kaolinite. Sand fraction is dominated by resistant minerals like quartz, zircon and weatherable minerals like mica, feldspars and chlorite and silt fraction contains same minerals as that of sand along with kaolinite. Initial water soluble K (WS-K), exchangeable K (Exch. K), non exchangeable K (Non Exch. K), lattice K and total K were 9.20, 41.00, 1020.00 8856.00 and 9480.00 mg kg-1 respectively in the upper surface (0-15 cm) of the soil. In the lower surface the values were 5.40, 28.40, 1454.00, 10222.00 and 10885.00 mg kg-1 respectively for WS-K, Exch. K, Non Exch-K, Lattice K and total K. In incubation study, where biofertilizers (T2 and T4) and organic manures (T9 and T10) were applied increase in WS-K was found with progression of the incubation period and in field study, it was highest with 21.35 mg kg-1 in the plot receiving T10 = INM Package (50% NP + Full K + 5t/ha Vermicompost) and was the lowest 8.17 mg kg-1 in the control plot. A perceptibly significant increasing trend of Exch-K was found, irrespective of the nutrient source except control treatment in incubated soil. In field condition, Exch. K corresponded to the amount of chemical K fertilizer applied and also to the INM package including microbial consortia and highest amount was observed in INM Package (50% NP + Full K + 5t/ha Vermicompost). Exchangeable K was found to be highly and significantly correlated with available K (r= 0.993**), non-exchangeable K (r=0.602*), total K (r=0.826*) and lattice K (r=0. 769**). With the increase in incubation time the non exch. K decreased in the treatments T2 = Microbial consortia (Azospirillum + PSB + KSB) @ 4 kg/ha, T4 = 100% RDF + KSB @ 4 kg/ha and T6 = Potassium nano-fertilizer @ 100 ml/1.2 L. Lower values of non-exchangeable K were recorded in all the treatments with different levels of potassium as compared to initial (1.020 mg kg-1) in the field experiment maximum being found in 100% RDF application. The increase of non exchangeable K in the control treatment with concurrent decrease in exchangeable K indicates the existence of dynamic equilibrium among different forms of potassium. Lattice K content of the treatments varied differently with different treatments but the changes were statistically insignificant in all the treatments in 40 DAI (Days after incubation) to 60 DAI and the changes was statistically at par in 60 to 90 DAI. Maximum amount of lattice was recorded in plot receiving 100% K fertilizer along with N & P fertilizers and INM components while lowest was recorded in plots which did not receive any fertilizer in field condition. The lattice K was significantly and positively correlated with available K (r= 0.791*), water soluble K (r=0.801**), exchangeable K (r=0.769*), nonexchangeable K (r=0.697*) and total K (r=0.865**). Increased levels of fertilizers brought about significant increase in total K content i.e. in the treatments where application of full dose of recommended fertilizers were done the total K tended to increase. In field condition, treatments where 100% K fertilizers were applied alone or in combination with INM components for 2 years continuously observed an increase in total K, highest being observed in T10 = 100% NP + Full K + 5 ton/ha Vermicompost) (11015.50 mg kg-1). Highly significant positive correlation values among various forms of K implied the existence of dynamic equilibrium. The amount of K released in successive extraction with boiling 1N HNO3 decreased step wisely in all treatments and reached to a constant level at 8th number of extraction. Reverse was happened in cumulative K. K release was higher in INM packages than plots received either organic or inorganic fertilizer alone. Cumulative K release was significantly correlated to lattice K (r=0.881**) suggesting that 1.0 mol L−1 HNO3 chiefly extracted K from nonexchangeable K pool in the soil. The amounts of step K of the treated soils ranged within a limit of 1837.0 to 3529.0 mg kg-1, which is high and thereby expected to be nonresponsive to K fertilization for a longer duration to the growing crops. The absolute amount of K fixed in soil progressively increased while percent K fixation decreased with increase in level of added K in all the treatments. Least percent K fixation was observed in T10 and the maximum in control. As this soil contains minerals like mica, vermiculite and smectite in clay fraction so K fixation is also high in this soil. Grain and straw yield was significantly affected by various treatments with the highest yield (= 56.22 q ha-1) in T10 which received 100% NP + Full K + 5 ton /ha vermicompost and the lowest in control. Yield was always better in INM package plots. Grain yield exhibited significant positive correlation with NPK uptake (r = 0.891**, 0.946** and 0.970**), water soluble K (r = 0.785**) exchangeable K (r = 0.897**) and available K (0.867**), suggesting their availability to rice crop. The highest potassium use efficiency (PUE) of 51.96% was found in the plot receiving 50% NP + Full K + 5 t/ha Vermicompost (T10) while the lowest of 40.49% in the plot receiving Potassium nanofertilizer @ 100 ml/1.2 L of water (T6) treatment. The information generated in the present study related to the status and distribution of different forms of potassium and its availability, releasing behavior and fixation evaluated through plant utilizable non-exchangeable K i.e. step K and constant rate K gave a general idea about the availability of K under the influences of varying doses of applied K and INM packages. Finally it can be concluded that INM Packages were found to be better for maintaining available K status, K release from none available pools and low K fixation in the soil and the resultant crop yield compared to inorganic treatments.ThesisItem Open Access ASSESSMENT OF ZINC USE EFFICIENCY IN MAIZE-MAIZE CROPPING SEQUENCE(2022) Borah, Sanjib Ranjan; Basumatary, AnjaliA field experiment was conducted at Krishi Vigyan Kendra, Jorhat farm, Kaliapani, Teok, Assam Agricultural University during 2018-19 and 2019-20 to study the influence of zinc fertilization on zinc fractions in soil, its relationship with important soil properties, yield, nutrient uptake and zinc use efficiency in maize-maize cropping sequence. The experiment was laid down in a randomized block design (RBD) with twelve treatments consisted of zinc applied as soil with or without foliar application through zinc sulphate and zinc oxide nano particle (ZnO NPs). Distribution of different zinc fractions in soil were assessed after harvest of each crop in the sequence. Perusal of experimental findings revealed that zinc fertilization had a significant influence on different zinc fractions in soil during both the years under investigation. The study revealed that among the zinc treatments, soil application of Zn @ 3.75 kg ha-1 in combination with foliar application of 500 ppm ZnO NPs exhibited the highest water soluble plus exchangeable-Zn content of 1.10 mg kg-1 in soil. The highest concentration of complexed-Zn (2.95 mg kg-1), amorphous sesquioxide-bound- Zn (4.11 mg kg-1), crystalline sesquioxide-bound-Zn (3.76 mg kg-1), residual-Zn (125.65 mg kg-1) and total-Zn (137.33 mg kg-1) were recorded in the treatment receiving soil application of Zn @ 7.5 kg ha-1. Among the zinc fractions studied, the concentration and percent contribution of water soluble plus exchangeable-Zn to total-Zn was the lowest while residual-Zn fraction contributed the highest to the total soil zinc pool. Path coefficient analysis showed that the water soluble plus exchangeable-Zn had the highest contribution towards the DTPA extractable-Zn in soil. The distribution of different zinc fractions at post-harvest soil was found in the following order: water soluble plus exchangeable-Zn < complexed-Zn < crystalline sesquioxide bound-Zn < amorphous sesquioxide bound-Zn < residual-Zn. All the fractions of zinc were found to be significantly and positively correlation with each other indicating existence of dynamic equilibrium of zinc in soil. Zinc fertilization exerted a significant influence on available nutrient status of soil. The highest available nitrogen content of 182.50 kg ha-1 was found in the treatment receiving soil application of Zn @ 3.75 kg ha-1 in combination with foliar application of 500 ppm ZnO NPs. The available phosphorus content in soil was decreased with zinc fertilization and thus, soil application of Zn @ 7.5 kg ha-1 recorded the lowest available phosphorus content of 19.45 kg ha-1, while the highest phosphorus content of 23.74 kg ha-1 was recorded in the control. However, no significant influence of zinc fertilization on available potassium, exchangeable calcium and exchangeable magnesium content in the post-harvest soils were observed. The highest available sulphur content of 25.50 kg ha-1 was registered in the treatment receiving soil application of Zn @ 7.5 kg ha-1. In respect of content of available micronutrients in soil, the DTPA extractable Fe, Cu and Mn content in soil were decreased with Zn fertilization and the highest content of DTPA extractable Fe (37.38 mg kg-1), Cu (0.42 mg kg-1) and Mn (9.26 mg kg-1) in soil was recorded in the control treatment, whereas, the lowest content was found in the treatment receiving Zn @ 7.5 kg ha-1. Application of 500 ppm ZnO NPs as foliar with soil application of Zn @ 3.75 kg ha-1 recorded significantly the highest DTPA extractable Zn content of 1.33 mg kg-1 in the post harvest soil. The study also revealed that zinc fertilization significantly influenced the grain and stover yield of maize. Perusal of pooled data indicated that among the zinc treatments, combined application of 500 ppm ZnO NPs as foliar with soil application of Zn @ 1.25 kg ha-1 registered the highest grain yield (65.04 q ha-1), stover yield (80.39 q ha-1) and harvest index (46.95%) in maize- maize sequence. Zinc fertilization exhibited a significant influence on uptake of major as well as micronutrients by maize. The highest uptake of nitrogen, potassium, calcium and magnesium by maize crops were recorded in the treatment receiving soil application of Zn @ 1.25 kg ha-1 in combination with 500 ppm ZnO NPs as foliar. The highest uptake of phosphorus by grain (14.81 kg ha-1) and stover (18.22 kg ha-1) was recorded in the treatment receiving 500 ppm ZnO NPs as foliar whereas, the highest sulphur uptake by grain (9.95 kg ha-1) and stover (11.72 kg ha-1) was found in the treatment receiving combined application of 500 ppm ZnO NPs as foliar with soil application of Zn @ 3.75 kg ha-1. Among the micronutrients, the highest uptake of Fe (214.56 g ha-1), Cu (31.99 g ha-1), Mn (56.33 g ha-1) and Zn (156.36 g ha-1) by maize grain was found in the treatment receiving combined application of 500 ppm ZnO NPs as foliar with soil application of Zn @ 1.25 kg ha-1. The highest uptake of Fe (846.24 g ha-1), Cu (45.99 g ha-1), Mn (248.57 g ha-1) and Zn (279.58 g ha-1) by maize stover was also found in the same treatment. Analysis of pooled data indicated that method of zinc fertilization had significant influence on zinc use efficiency by maize. The highest agronomic efficiency (2382.51 kg kg-1), apparent recovery efficiency (36.88%), zinc utilization efficiency (4067.44 kg kg-1) and partial factor productivity (16913.19 kg kg-1) was recorded in the treatment receiving foliar application of 500 ppm ZnO NPs. The highest physiological efficiency (12816.13 kg kg-1), agro physiological efficiency (7567.77 kg kg-1) was recorded in the treatment receiving combined application of 500 ppm ZnO NPs as foliar with soil application of Zn @ 1.25 kg ha-1. Cost benefit analysis revealed that among different treatment combinations, the highest gross return (Rs. 1,17,072.00), net return (Rs. 82,773.00) and highest B-C ratio (2.41) was registered in the treatment receiving 500 ppm ZnO NPs as foliar in combination with soil application of Zn @ 1.25 kg ha-1. Considering improvement of crop yield and economic return, combined application of 500 ppm ZnO NPs as foliar with soil application of Zn @ 1.25 kg ha-1 was found to be superior over other treatmentsThesisItem Open Access ASSESSMENT OF SOIL ERODIBILITY AND PRODUCTIVITY POTENTIAL FOR WINTER RICE IN A TRANSECT OF JIYADHOL RIVER BASIN, ASSAM(2021) Saikia, Rituparna; Patgiri, D. K.Soil erosion is a major environmental problem in developing countries like India, where agriculture is the main economic activity of the people. The present investigation aims to assess the soil erodibility and productivity potential for winter rice in a transect of Jiyadhol river basin with respect to landform characteristics, morphometry, erosion hazard and potential for growing rice. The study area extends from 27.335 N to 27.574 N latitudes and 94.294 E to 94.540 E longitudes, covering an area of 47,389.13 ha. Based on topographical variation in satellite data, four distinct landform units were delineated which includes: piedmont plain (9,097.69 ha), upper alluvial plain (9,594.9 ha) lower alluvial plain (13,706.57 ha) and flood plain (14,977.0 ha). The drainage map identified the transect as fifth order drainage basin with higher no‘s of first order streams making it vulnerable to erosion hazard. There was significant variation of slope, physiographic structure and infiltration capacity across the basin. The mean bifurcation ratio (3.56) indicated that the basin is underlined by uniform materials and streams are branched systematically. Relatively lower value of ‗Rho‘ coefficient indicated meager capacity of hydrologic storage during the period of floods that could leads to higher runoff. The relatively higher drainage density (0.91 km km-2) could be the results of impermeable subsoil material, sparse vegetation and high relief. The drainage intensity (0.43) indicated that the basin area was highly susceptible to flooding and gully erosion. The elongation ratio, circulatory ratio, form factor ratio and shape factor indicated that the shape of the studied transect was nearly circular. Such basins are highly erosion prone as compared to elongated basins. A total of 170 no of geo-referenced surface (upto 30 cm) soil samples were collected for analyzing soil physico-chemical, hydro-physical and fertility related parameters. There was a decreasing trend in total sand and very fine sand content in soils from piedmont plain toward flood plain. Whereas, silt and clay content increases from piedmont plain towards flood plain. The textural properties of studied soils varied from loamy sand to clay loam; sandy loam was the dominant texture. The structural properties of studied soils varied from sub angular blocky to massive. Among the different landform units the highest bulk density was recorded in the piedmont plain soils (Mean 1.5 Mg m-3). The pH in the studied soils varied from very strongly acidic to slightly acidic (4.69 to 6.47). 69.4% of the total area was strongly acidic and 4.3% of the area was very strongly acidic. Cation exchange capacity, exchange capacity of clay, apparent cation exchange capacity and exchangeable cations were higher in flood plain soil which may be linked to corresponding higher clay and soil organic matter content. Likewise, the status of soil organic carbon, available nitrogen, available phosphorus and available potassium was high in soils of flood plain. Soils of flood plain exhibited higher macro-aggregation owing to higher clay and soil organic matter. However, piedmont plain soils exhibited higher microaggregate content. Soil erodibility indices viz., silt clay ratio, clay ratio, modified clay ratio, dispersion ratio, erosion ratio showed that piedmont plain soils are more susceptible to soil erosion. The geospatial assessment of their variability clearly prioritizes the areas with higher erosion susceptibility, where, suitable management practices may be undertaken to increase soil productivity. The findings from erodibility indices were further corroborated by soil loss assessment by universal soil loss equation, which revealed that 38.5 percent area was under severe soil loss. The areas in higher elevation were under higher soil loss and vice versa. The piedmont soils, affected by very severe erosion hazard (average soil loss of 34.80 t ha-1 yr-1) which might be due to dominating factors like higher relief, steep slope, lighter texture and weaker structure, hence need immediate adoption of conservation measures. The soil productivity and potentiality index was evaluated as per the procedure suggested by Riquir et al. (1970). Piedmont plain soils having productivity index values from 12.1 to 35.1 (Mean 23.0) were rated as poor to average classes. The acidic pH, low organic matter, low base saturation and coarse texture being the major limiting factors for crop production. The piedmont plain (Mean 2.01) and upper alluvial plain (Mean 1.79) soils had more coefficient of improvement as compared to lower alluvial plain (Mean 1.60) and flood plain (Mean 1.57) soils. Majority of the piedmont plain soils are found to be unsuitable for growing Sali, Ahu and Boro rice and the corresponding yield of Sali rice was also quite low. Therefore alternate crops may be grown with suitable irrigation facilities. The negative relationship of soil loss with rice yield, productivity, potentiality and suitability indicated that greater soil loss leads to decrease in productivity of soils. The potential productivity index value was higher for piedmont plain soils. Significant positive relationship was obtained between normalized difference vegetation index during peak vegetative stage with yield, soil organic matter, mean soil site suitability index for Sali rice and crop yield index in the first year of study Summarizing above results it may be concluded that the Jiyadhol river basin transect is a fifth order watershed with high vulnerability to soil erosion. Majority of the soils of the study area have high soil erodibility owing to poor soil physical properties as well as topographical position. Geospatial assessment of soil loss has clearly delineated areas with severe soil loss, hence, based on this suitable conservation measures may be effectively adopted. Moreover, while formulating site specific crop management plan GIS based thematic maps of soil properties and erodibility may be taken as ready reckoner to augment productivity, profitability and sustainability of cropping systems in the area.ThesisItem Open Access SPATIAL ANALYSIS OF HEAVY METALS IN SOIL, PLANT AND GROUNDWATER IN NAGAON DISTRICT OF ASSAM USING GIS TECHNIQUE(2022) Hazarika, Prarthana Priyom; Medhi, Dr. B. K.Geospatial as well as geostatistical approaches using GIS tool to assess and characterize heavy metals namely Cd, Cr, Cu, Ni, Zn, Pb, Fe, As and Mn in soil, crop, and groundwater, their degree of pollution level, and phytoextraction behaviours of key metals were carried-out in Nagaon district of Assam during 2018 to 2021. To appraise the potential heavy metal sites, a random systematic method was used for sampling strategy by dividing the study area into a grid of 5 km× 5 km and collecting 160 composite soil samples from 0-15 cm depth for the total content of heavy metals using Atomic Absorption Spectrophotometer (Model: iCE 3500, Thermofisher). Geospatial analyses from different thematic maps of heavy metals revealed significant vulnerable points of elevated concentrations of Cd (> 0.31 mg/kg ), Pb (> 24.45 mg/kg ) and Ni (> 0.05 mg/kg ) in soils and Cd (>0.01 mg/L), Cr (>0.05 mg/L), Cu (>1.3 mg/L ), Fe (> 0.3 mg/L ), As (> 20 mg/L ) and Mn (> 0.1 mg/L ) in groundwater which is presumed to be due to anthropogenic factors. Geospatial interpolation pedagogies like Inverse Distance Weighted, Global Polynomial Index, Local Polynomial Index, Kriging, Kernel Smoothing and Diffusion Kernel were tested to estimate the metal concentrations at unsampled locations for assessment of their performance by comparing the Root Mean Square Error (RMSE) for cross-validation and all models provided more or less high prediction accuracy to mean value of the metals. Specific to the Kriging model, it was found to be best fitted with the lowest RMSE in all the metals except Mn and Ni in the soil where IDW and local Polynomial index was found to give the lowest RMSE. Other geospatial models that interpreted better groundwater heavy metals content with lowest RMSE were Inverse Distance Weighted Interpolation for Ni and Pb, Local Polynomial Index for Mn, Global Polynomial Index for Fe. The three-dimensional trend over the distribution of metals throughout the district best fitted the secondorder polynomial for Cd, Cu, Ni, Zn, Pb, Fe, As, and Mn in soils while both first and second-order polynomials according to XZ and YZ dimensions fitted well for Cd, Ni, Mn, Pb, Ni, and Cu in groundwater. Significant numbers of pairs of heavy metals to a certain extent were found to be spatially autocorrelated and all the pairs away from X-axis towards the extreme right corner and far above the axis reflected less influence of local characteristics of the heavy metal. Spatial autocorrelations were detected for 9 heavy metals and the autocorrelation distances were; Cd 60; Cr 60; Cu 60; Ni 55; Zn 57; Cu 55; Pb 65; Fe 68; As 62 and Mn 65 km for soil and Cd 60 Cr 57; Ni 65; Zn 57; Pb 60; Fe 65; As 57and Mn 60 km for groundwater. Co-variance cloud with search direction from North to South revealed the existence of spatial autocorrelation revealing a wider spatial shift of correlation towards the southern direction. The Pollution Indices (Single Pollution Index, Geo-accumulation Index, Ecological Risk Factor) showed the highest threat to the soil from Pb, Cd, and Ni respectively. Overall Multi Pollution Indices (Pollution Load Index, Average Single Pollution Index, Enrichment Factor, and Nemerow Pollution Index) encompassing all the metals showed that although there was considerable pollution in the soil, the soil was under the critical limit but towards the higher side. The Bio-concentration, Bio-accumulation, and Translocation Factor as was revealed from the pot culture experiment taking toria (variety TS-67) as test crop was found below 1 for all the graded levels of Pb envisaging the crop inefficient to hyperaccumulate, phyto-stabilize and phyto-extract Pb from the soil. A higher value of Bio-concentration Factor (>1) for Cd and Ni, revealed the crop efficiently hyper-accumulates Cd and Ni. BAF (>1) for Cd levels at 0.5 ppm, 1.0 ppm, and 1.5 ppm and Ni levels baring 60 ppm indicated the crop to be able to phytostabilises both Cd and Ni at lower concentrations. The Translocation Factor (< 1) for Cd and Ni was indicative of the inefficiency of toria to phytoextract Cd and Ni in its aerial parts. The study helped to find out the hotspots for certain heavy metals in the district which would certainly help in further decision making and take viable removal measures as well as suitable cropping systems. GIS maps validated through geostatistical approaches help in contributing contamination characteristics, degree of pollution of heavy metals in soils as well as groundwater based on which desired phytoremediation planning may be adopted.ThesisItem Open Access INFLUENCE OF FERTILIZER MANAGEMENT PRACTICES ON POINT OF ZERO CHARGE (PZC) IN SOILS OF ASSAM AND ODISHA(AAU, Jorhat, 2021) Parija, Subhra; Nath Das, KulendraAn incubation study was undertaken to examine the influence of fertilizer management practices on the point of zero charge (PZC) in soils of Assam and Odisha. Six number of geo-referenced surface soil samples (0-15 cm) viz., black soil (Vertisol), laterite soil (Alfisol), red soil (Alfisol) and three alluvial soil samples belonging to Entisol, Inceptisol and Alfisol were collected from Kalahandi, Khordha and Dhenkanal districts of Odisha and Dergaon, Golaghat, ICR Farm AAU, Jorhat and Titabor, Jorhat of Assam, respectively. The soils strikingly varied in their mechanical composition, bulk density and moisture content at field capacity. The soils were mostly acidic in nature (pH 5.04 – 5.71) except black soil of Odisha which was slightly alkaline (pH 7.93). Organic carbon in Odisha soils ranged from 0.21 - 0.95% and lied between 0.47 - 0.86% in soils of Assam. All the soils were low to medium in available NPK but exhibited high content of available S. Laboratory incubation of these soils (200g) were carried out after treatment with four different fertilizer management practices viz., FYM @ 5 t ha-1 (T1), NPK @ 80:40:40 for Odisha soils and 60:20:40 for Assam soils (T2), FYM @ 5 t ha-1 + NPK @ 80:40:40 for Odisha soils and 60:20:40 for Assam soils (T3) and FYM @ 5 t ha-1 + NPK @ 80:40:40 for Odisha soils and 60:20:40 for Assam soils + Lime requirement/ Gypsum requirement (T4), in three replications. Sub samples were drawn after an interval of 15 and 30 days after treatment (DAT) and analysed. The PZSE and PZNC of the incubated samples were estimated through potentiometric titration and ion retention methods, respectively. Pearson’s correlation coefficient between PZC components and relevant soil properties was studied. The effect of the applied treatments on the PZC components and nutrient availability was evaluated using ANOVA for CRD. Results revealed that the PZSE for Odisha soils ranged from 2.18 to 4.70 and lied between 3.60 and 4.16 for the soils of Assam. The PZNC was achieved at comparatively lower pH values, ranging from 2.03 to 4.10 for Odisha soils and from 2.50 to 3.61 for Assam soils. The order of PZC for the samples was in direct correlation with their respective sesquioxide contents. Factors like clay, organic carbon, exchangeable calcium and available phosphorus imposed a significant influence on soil PZC values. The treatment T2 resulted in highest availability of the primary nutrients for all the soils under incubation while maximum availability of secondary nutrients was recorded under treatment T4. Availability of all the nutrients decreased at 30 DAT as compared to that of 15 DAT, except for Ca and Mg where the availability was more at 30 DAT. The treatment effect was insignificant on the sesquioxides content of incubated soils. Highest values of PZSE and PZNC were recorded under treatment T2 followed by T3, T4 and T1 for all the incubated soil samples of Odisha and Assam, however there was a decrease in the PZC values with increase in days of incubation. Such results confer that these soils allow more availability of anionic nutrients such as nitrate (NO3 -), phosphate (PO4 3-), sulphate (SO4 2-) immediately after fertilizer application, which slowly decreases with time favoring an increased CEC in the latter phase and thereafter enhancing the availability of cationic nutrients such as ammonium (NH4 +), potassium (K+), calcium (Ca2+), etc. In comparison to other treatments, the treatment T4 consisting of organic manures, recommended dose of chemical fertilizers along with lime/gypsum resulted as the most ideal fertilizer management practice. Besides providing optimum amount of primary nutrients and maximum amount of secondary nutrients, it regulated the PZC values favouring minimal loss of nutrients leading to enhanced crop production.
