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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 SYMBIOTIC EFFECTIVENESS OF COMMON BEAN (PHASEOLUS VULGARIS L.) RHIZOBIUM GROWN IN SOILS OF ASSAM(AAU, Jorhat, 2020-09) Kalita, Jyotirupa; Nath, Dhruba JyotiNodulation promiscuity and sparse nodulation in common bean (Phaseolus vulgaris L) are two important intrinsic characteristics besides soil chemical factors for low nitrogen (N2) fixation compared to other grain legumes. The symbiotic effectiveness of Rhizobia in nodulation is significant in Rhizobium strain selection programme to avoid the risk of sub optimal nodulation or nodulation failure. The present study was carried out to screen the effective native Rhizobia isolates from field grown common bean for their symbiotic effectiveness. Root nodules and rhizosphere soil were collected from thirteen different common bean growing sites representing three districts viz: Jorhat, Golaghat and Karimganj of Assam for isolation of Rhizobium and to assess their symbiotic effectiveness. Prior to isolation of Rhizobium, the nodulation characteristics of field grown common bean were assessed in correlation with selected soil chemical parameters. The study established the significant variation of nodule number (15.33 -173.67 /plant) and nodule dry weight (8 to 77.67 mg /plant) across the sites and the variation could be attributed to soil organic carbon (r=0.75*, r=0.82*) and available P2O5 in the rhizosphere (r=0.56*, r=0.57*) respectively. The frequencies of purified Rhizobia isolated from the nodules using differential Yeast Extract Mannitol Agar containing congo red (YEMA-CR) media, similarly varied significantly (5.38 to 8.58 log cfug-1) with typical colony characteristics across the sites.Growth in YEM broth exhibited the maximum population ranges (7.29 - 8.60 log cfu mL-1) at 48h, while optical density at 550nm (0.016-0.035) remains maximum at 72h of incubation. Optimum growth was exhibited by the isolates at pH7 and temperature 30o C. Differences in response to intracellular and extracellular enzymes activities, carbon sources utilization, amino acids utilizations, intrinsic antibiotic resistance and release of polysaccharides were observed for isolated Rhizobia. The assesment of changes in shoot root ratio (-54.29 to 180.00), nitrogen content in shoot (4.76-19.01mg plant-1), nodule number (11.40-70.80), nodule dry weight (0.02 to 0.20g), nodule score (3.60-7.00), symbiotic efficiency (213.00-852.00) and relative strain efficiency (3.98-41.3) in ‘Leonard Jar’ assembly exhibited the symbiotic effectiveness of few promising (R01, R06 and 18P) isolated Rhizobium. The linear correlation between shoot dry weight and shoot nitrogen content with nodule dry weight (r=0.65*), further establishes the fully functional N2 fixation system as a result of effective nodulation.ThesisItem Open Access SOIL NUTRIENT ASSESSMENT AND GHG EMISSIONS OF PUDDLE RICE SOILS UNDER INTEGRATED NUTRIENT MANAGEMENT PRACTICES(AAU, Jorhat, 2020-05) Gogoi, Bhabesh; Borah, NilayThe present work was carried out during 2016-2018which forms a part of the long-term Permanent Plot Experiment on Integrated Nutrient Supply System in Cereal Based Cropping Sequence laid out during 1987-1988 under All India Coordinated Research Project on Integrated Farming System at Assam Agricultural University (AAU), Jorhat. The experiment was laid out in a randomized block design at Instructional-cum- Research Farm, Assam Agricultural University, Jorhat replicating 3 times with 8 treatment combinations viz.,T 1 : no fertilizer, no organic manure (control), T 2 : 100% RDF (chemical), T 3 : 50% RDF (chemical) + FYM @ 2.5 t/ha for winter rice and 100% RDF (chemical) for autumn rice, T4 : 75% RDF (chemical) + FYM @ 1.25 t/ha for winter rice and 75% RDF (chemical) for autumn rice, T 5 : 50% RDF (chemical) + rice stubble @3.0 t/ha for winter rice and 100% RDF (chemical) for autumn rice, T 6 : 75% RDF (chemical) + rice stubble @1.5 t/ha for winter rice and 75% RDF (chemical) for autumn rice, T 7 : 50% RDF (chemical) + Azolla @ 0.5 t/ha for winter rice and 100% RDF (chemical) for autumn rice, T 8 :75% RDF (chemical) + Azolla @ 0.25 t/ha for winter rice and 75% RDF (chemical) for autumn rice. Results revealed that the application of 50% RDF (chemical) + Azolla @ 0.5 t ha-1 in case of winter rice and 100% RDF (chemical) in case of autumn rice (i.e. T7) showed the highest NH4-N, NO3-N and available N content in soil followed by the application of 50% RDF (chemical) + FYM @ 2.5 t ha-1 in winter rice and 100% RDF (chemical) in autumn rice (i.e. T3) in case of the rice-rice sequence after 32 cycles of the cropping. On the other hand, different fractions of P (viz., available P, Occluded P, Saloid P, Ca-bonded P and total P) and K (viz., water soluble K, available K, exchangeable K, non-exchangeable K, lattice K and total K) were found maximum in case of T3 followed by T5. Different fractions of C in rice soil were increased and varied significantly due to INM practices over unfertilized control (T1). The total organic carbon (TOC), total inorganic carbon (TIC) and total C was found to be highest in case of T3; whereas, the highest content of Walkley & Black C, less labile C and non-labile C in soils were recorded in case of T5. Yet again, T7 [50% RDF (chemical) + Azolla @0.5 t ha-1 in winter rice and 100% RDF (chemical) in autumn rice] was registered with the maximum content of water soluble C, microbial biomass C, very labile C and labile C in the soils underricerice system. In this study, all the fractions of NPK and C were found to be lowest in T1 (unfertilized control) treatment. The sensitivity index revealed that the microbial biomass C and water soluble C fractions were the most sensitive ones for different nutrient management practices as compared to other C fractions under study; whereas, the lowest sensitive fractions included non-labile C, less labile C, total inorganic C, total organic C andtotal C. Data on SOC stock due to INM practices varied significantly from 39.11 Mg ha-1 under T1 (unfertilized control) to 67.14 Mg ha-1 under T3(receiving FYM @2.5 t ha-1 + chemical fertilizers).The soil C sequestration ranged between (-)2.77 Mg ha-1 under T1 and 24.07 Mg ha-1 under T3. Over the control treatment (T1), 41.81 to 71.67% build up of C in the soils were recorded due to various INM treatments after 32 years of rice-rice cropping sequence. In this study, the highest bacterial population was recorded in case of T7(receiving Azolla @0.5 t ha-1 + chemical fertilizers); whereas, fungal population was found maximum in case of T3 (receiving FYM @2.5 t ha-1 + chemical fertilizers). Various 6 soil enzymes viz. dehydrogenase (DHD), phosphomonoeaterase (PMEase), fluorescein diacetate (FDA) and urease, involved in energy flow and nutrient cycling showed significantly higher activities under INM treatments. Significantly highest activity of DHD and urease was found in T7, while PMEase and FDA hydrolysis activities were found to be maximum in T3.There was a decrease in all the enzymatic activities over initial in the unfertilized control treatment (T1) after 32 years of rice-rice cropping. The pattern of CO2, CH4 and N2O emissions under rice-rice cropping system varied significantly with the stages of rice growth as well as by the different INM treatments under study. The CO2 and CH4 emissions peaked at 60 days after transplanting (DAT) of winter rice (cv. Ranjit) and 45 DAT of autumn rice (cv. Disang). On the other hand, N2O emission peaked first at 30 DAT and secondly at 60 DAT of winter rice (cv. Ranjit) in case of all the treatments except unfertilized control. However, only one N2O emission peak was observed at 45 DAT in case of autumn rice (cv. Disang) under study. The highest emissions of CO2 and CH4 during winter crop (cv. Ranjit) were observed in case of T5 receiving rice stubbles @3.0 t ha-1 + chemical fertilizers. In contrast, N2O emission during winter crop cv. Ranjit initially (up to 45 DAT) was found to be highest in case of the T2 (100% RDF, chemical); and afterwards, highest N2O emission was observed in case of T7 receiving Azolla @ 0.5 t ha-1 + chemical fertilizers. In case of autumn rice (cv. Disang), the maximum emissions of CO2, CH4 and N2O were recorded in T5(receiving rice stubbles@3.0 t ha-1 + chemical fertilizers). The lowest CO2, CH4 and N2O emissions were recorded in T1. It was evident in this study that the GHG emissions for the control (T1) and for Azolla cover + chemical fertilizer treatments (i.e. T7 and T8) were relatively low and similar during the initial stages of winter rice cv. Ranjit (up to 60 DAT) and autumn rice cv. Disang (up to 30 DAT). Among all the organic sources, supplementation of Azolla along chemical fertilizers resulted maximum reductionin GHG emissions from rice-rice system over FYM and ricestubbles. Pearson correlation matrix between the GHGs indicated that the emission of CO2 had a positive and significant correlation with CH4 (r=0.874**)and N2O (r=0.748*)emissions from the rice-rice cropping system. However, the correlation between the CH4 and N2O emission was positive and non-significant (r=0.623NS)in this study. Significant and positive correlation of CO2 and CH4 emissions from rice-rice cropping system were recorded with different fractions of C viz., WSC, WBC, MBC, VLC, LLC, LC, NLC, TOC and TC. The correlations of N2O emission with NH4-N, NO3-N and available N were found to be significant and positive; whereas, it was positive but nonsignificant with total N in soil. Likewise, microbial activities, enzymatic activities in soil and yield and yield attributing characteristic of rice crop were positively correlated with the emissions of CO2, CH4 and N2O from the rice-rice system of cropping. Yet again, in this study, GHGs were found to have not significant correlation with the plant height of rice crop. Overall, the findings of the present study lead to the conclusion that application of 50% RDF (chemical) + rice stubbles @ 3.0 t ha-1 in winter rice (cv. Ranjit) followed by 100% RDF (chemical) in autumn rice (cv. Disang) i.e. T5 could be considered as the best nutrient management practice for the rice-rice sequence in terms of highest yield (7.27 Mg ha-1), gross return (67.72 ×103 Rs. ha-1) andnet return(39.79 ×103 Rs. ha-1)with a B:C ratio of 2.42 in one way, enhancing the soil health under long run condition, in other. However, so far as the issue of GHG emission and global warming is concerned, application of 50% RDF (chemical) + FYM @ 2.5 t ha-1 in winter rice and 100% RDF (chemical) in autumn rice (2nd best treatment in terms of soil properties and yield with the B:C ratio 2.41) may be considered as better option for rice-rice cropping system under the prevailing climatic condition of Assam.ThesisItem Open Access PROFILE DISTRIBUTION OF POTASSIUM IN SOME SOILS OF SARUPATHAR BLOCK OF GOLAGHAT DISTRICT, ASSAM(AAU, Jorhat, 2020-09) Das, Karabi; Dutta, MaramiThe present investigation was carried out with the objectives to characterize and classify the soils and to study the profile distribution of different forms of potassiumin some soils of Sarupathar Block of Golaghat District, Assam. Horizonwise soil samples from five pedons in different locations viz., P1 (rice), P2 (rice), P3 (rice), P4 (vegetable) and P5 (upland trees) were collected. The soil colour (moist) varied considerably ranging from dark yellowish brown (10YR 4/4) to very pale brown (10YR 7/4) with dominant hue of 10YR in all the pedons. The colour value ranged from 4 to 7 and chroma ranged from 1 to 8. Mottles of higher chroma (6-8) were seen in subsurface horizons of P1, P2 and P3 and dominant hue of the colour of mottles was 7.5YR. A textural variation ranging from loam to silty clay was observed in surface horizons and sandy clay loam to clay was observed in sub-surface horizons. The structure of the soils varied from very fine to medium, weak to strong and sub angular blocky except for the surface horizon of P3 pedon where structure was massive. The sand content in the soils varied from 7.6 to 46.5 per cent, silt varied from 22.3 to 52.8 per cent and clay varied from 16.1 to 49.8 per cent. The value of bulk density for different pedons ranged from 1.35 to 1.50 Mg m-3. Organic carbon tended to decrease with depth in all pedons except for P4. The pH values were in acidic range in all the pedons and the pH values were lower in the surface horizons as compared to the subsurface horizons.Ca2+ was found to be the dominant cation followed by Mg2+, Na+ and K+ in all the pedons except in P5, where the sequence was Mg2+>Ca2+>Na+>K+. CEC of the soils ranged from 7.5 to 14.2 cmol (p+) kg-1 soil and per cent base saturation (PBS) ranged from 14.27 to 47.02. Available N and available P2O5 ranged from 65.80(L) to 487.60(M) and 8.21(L) to 28.78(M) kg ha-1, respectively. The studied soils were classified as Aquic Dystrudepts (P1), Oxyaquic Dystrudepts (P2), Typic Endoaquepts (P3), Typic Udifluvents (P4) and Typic Dystrudepts (P5) at subgroup level. Water soluble K status of the soils was found in the range of 0.85- 8.45 mg kg-1. Exchangeable K status of the soil samples was found to be in the range of 10.65 - 92.45 mg kg-1. Available K status of the soil samples was recorded in the range of 15.55 - 100.90 mg kg-1 in the studied pedons and contribution to total K was 0.15- 0.76 per cent. Status of non-exchangeable K was found in the range of 172.70 - 296.60 mg kg-1 which contributed 0.93-3.93 per cent of total K. No specific trend was seen in any of the profile in case of non-exchangeable K content. Lattice K status was found in 7 the range of 4365.30 – 19966.85 mg kg-1. The mineral pool of K is the main source of total K which accounts more than 90 per cent of the total K. The value of total K in the studied soils was found in the range of 4580 – 20200 mg kg-1. The results indicated that the pH of the soil samples showed significant positive relationship with nonexchangeable K (r = 610**). The organic carbon content of the studied soils showed positive and significant correlation with water soluble K (r = 416*). The cation exchange capacity of the soils showed a significant positive relationship with exchangeable, available, lattice and total forms of potassium. Highly significant and negative correlations were observed between exchangeable, available, lattice and total forms of potassium with total sand content of the soils. Clay showed significant positive relationship with exchangeable, available, lattice and total forms of potassium. Available K showed a significant and positive correlation with exchangeable K (r =0.994**), lattice K (r = 0.517**) and total K (r = 0.520**). The correlation coefficient between forms of potassium indicated that exchangeable K had significant positive correlation with lattice K (r = 0.569**) and total K (r = 0.571**).A highly significant and positive correlation was also found between lattice K and total K (r = 0.999**) in the studied soils of Sarupathar block of Golaghat district.ThesisItem Open Access NUTRIENT AVAILABILITY IN SOIL AND YIELD OF TOMATO AS INFLUENCED BY MANURE SOURCES AND RICE STUBBLE MANAGEMENT(AAU, Jorhat, 2020-09) Das, Anupama; Borah, NilayA field experiment was conducted in ICR farm, AAU, Jorhat from December, 2019 to April, 2020 to evaluate nutrient availability in soil and yield of tomato after winter rice (variety - Ranjit) as influenced by different organic manure sources with and without rice stubble incorporation. The experiment was conducted in a split plot design comprising individual plot size of 2.5 m x 2.1 m with four replications. Rice stubble was either removed or incorporated in the main plot, and each main plot was divided into five sub plots fertilized with different composts or recommended fertilizer dose (RDF). The nutrient management treatments comprised of unfertilized plot, RDF (farmyard manure 2 t ha-1 one week before planting followed by 75:60:60 N:P2O5:K2O kg ha-1 applied at planting, with N in two equal splits), farmyard manure 2 t ha-1 (FYM), poultry manure 2 t ha-1 (PM) and vermicompost 2 t ha-1 (VC). The composts were applied in two equal splits at planting and at 30 days after planting (DAP). The soil pH was significantly higher up to 56 DAP in poultry manure fertilized plots where soil exchange acidity was lowest among all the treatments. The NH4-N and NO3-N contents, and P and K availability in soil was highest with application of RDF, while the lowest values were observed in the unfertilized plot. The NH4-N, NO3-N and available P contents of soil significantly increased in VC and PM applied plots compared to FYM or unfertilized plots and were at par with RDF. However, the available K content of soil was significantly higher in RDF at 28 and 56 DAP compared to all other treatments. The exchangeable cations and soil enzyme activity at 28 DAP and 56 DAP showed significant increase in RDF, PM and VC. The highest tomato fruit yield was observed with RDF, which differed significantly over all the treatments, and was followed by PM and VC fertilized treatments. Incorporation of rice stubbles had a positive effect on nitrogen mineralization, availability of phosphorous, potassium, exchangeable cations, soil enzyme activity and yield of tomato, but the interaction with nutrient management was not significant.ThesisItem Open Access MORPHOMETRY, SOIL ERODIBILITY AND PRODUCTIVITY POTENTIAL OF A TRANSECT OF MORIDHAL RIVER BASIN IN DHEMAJI DISTRICT OF ASSAM(AAU, Jorhat, 2020-08) Bharteey, Prem Kumar; Deka, BipulThe present investigation was carried out to study the morphometry, soil erodibility and productivity potential of Moridhal river basin in Dhemaji district of Assam. The Moridhal watershed, encompassing 30,730 ha geographical area, is situated between 94052 E to 94069 E longitude and 27038 N to 27064 N latitude. Based on total variation in satellite data (Resourcesat-2, LISS-4), four distinct physiographic units of the Moridhal watershed were delineated which includes: upper piedmont plain (1,844 ha), lower piedmont plain (2,391 ha), alluvial plain (9,888 ha) and flood plain (16,607 ha). The stream order map of the Moridhal river basin was prepared by on screen digitization using Q GIS software and the morphometric parameters were evaluated through measurement of linear, areal and relief aspects. The drainage streams were delineated up to 4th order with stream numbers of 36, 14, 5 and 1, for I, II, III and IV order, respectively. The mean bifurcation ratio and Rho coefficient for the Moridhal watershed was computed to be 2.22 and 0.41, respectively. The computed value of aerial aspects like elongation ratio, circulatory ratio, form factor ratio and shape factor revealed elongated shape of the watershed area. The studied relief aspects include parameters like basin relief, relief ratio, ruggedness number, and relative relief. The calculated value of ruggedness number (0.03) and relative relief (0.055 per cent) indicated higher infiltration and lower runoff in the studied area. GPS based surface and core soil samples representing different physiographic units were collected and analyzed for various physico-chemical properties. The texture of the studied soils varied from loamy sand to clay, sandy loam being dominant. There was an increasing trend of very fine sand and silt content from upper piedmont plain to floodplain. The bulk density and particle density of studied soils varied from 1.10 to 1.67 Mg m-3 and 2.16 to 2.74 Mg m-3, respectively. The value of porosity, water holding capacity and hydraulic conductivity of the studied soils ranged from 24.99 to 54.68 per cent, 19.88 to 63.12 per cent, and 0.11 to 6.54 cm hr-1respectively. Field capacity and available water content showed significant positive correlation with clay content and porosity, while permanent wilting point exhibited significant positive correlation with sand content. The pH of the soils was extremely acidic (4.2) to slightly acidic (6.3). The electrical conductivity in the studied soils varied from 0.01 to 0.16 dS m-1 which was almost negligible. The cation exchange capacity of the studied soils varied from 3.88 to 19.40 cmol (p+) kg-1 with a mean value of 9.69 cmol (p+) kg-1. Amongst the exchangeable cations, Ca++ was found to be the dominant in the studied soils followed by exchangeable Mg++, K+ and Na+. The exchange capacity of clay and apparent CEC showed wide variation in the studied area. The base saturation varied from 33 to 83 per cent and the organic matter content was medium to high (range 5.50 to 29.60 g kg-1). The available N, available P2O5 and available K2O content varied from low to high with a range between 137.98 to 570.75 kg ha-1, 18.47 to 67.20 kg ha-1 and 37.23 to 549.16 kg ha-1, respectively. The nutrient index for available N, P2O5 and K2O were found to be 1.88 (Medium), 2.15 (Medium) and 1.32 (Low). The principal factor analysis, which was carried out using 35 characters, could explain 71.20 per cent of the total variance with the seven number of extracted eigen values. There was an increasing trend of macroaggregate from upper piedmont plain (mean 24.9 per cent) to flood plain soils (mean 47.4 per cent). The microaggregate in the studied soils varied from 17.8 to 89.8 per cent and the mean weight diameter ranged between 1.00 to 2.74 mm. The erodibility of the studied soils was assessed by computing various erodibility indices like clay ratio, silt clay ratio, modified clay ratio, dispersion ratio, erosion ratio and erosion index. The mean value of clay ratio, silt/clay ratio and modified clay ratio were found to be 4.02, 1.35 and 3.63, respectively. The dispersion ratio of the soils varied from 0.06 to 1.18 with a mean value of 0.19. It was observed that 48.82 per cent of the total studied soil samples had dispersion ratio values above 0.15 which may be considered as erodible. The erosion ratio and erosion index of studied soils varied from varied from 0.01 to 0.55 and 0.03 to 0.71, respectively. It was observed that almost all the studied physico-chemical properties influenced the erodibility indices to a great extent. The soil loss varied from very slight to very severe (range 0.87-67.77 t ha-1 yr-1) with a mean value of 16.19 t ha-1 yr-1. A significant positive correlation of soil loss was noticed with very fine sand (r = 0.229**), silt (r = 0.212**), microaggregate (r = 0.351**) and relief (r = 0.711**). The studied soils exhibited a decreasing trend of soil loss from upper piedmont plain towards flood plain. The productivity indexes of the studied soils varied from 12.13 to 62.14 with a mean value of 35.22. The potentiality index and coefficient of improvement values of studied soils varied from 41.04 to 90.25 and 1.11 to 4.69, respectively. Soil site suitability criteria for crops viz., Sali rice, Ahu rice, Boro rice, wheat, mustard/rapeseed, sesame, pea, potato, onion and coconut were evaluated. The study revealed that the soils were permanently unsuitable (N1) to moderately suitable (S2) for Sali rice, Ahu rice, Boro rice, wheat, pea, mustard/rapeseed, sesame, potato, onion and coconut. Major constraints identified in the watershed lies in acidity, organic carbon, texture, flooding, drainage and low precipitation in early growth stage during rabi season. GIS based maps for various themes like pH, organic matter, available N, available P2O5, available K2O along with soil loss, productivity, potentiality, and soil-site suitability for studied crops were also prepared to depict the spatial distribution under different classes.ThesisItem Open Access MORPHOMETRIC EVALUATION AND SOIL LOSS ESTIMATION OF A TRANSECT OF SUBANSIRI WATERSHED IN LAKHIMPUR DISTRICT OF ASSAM(AAU, Jorhat, 2020-08) KISHORE, KAMAL; Deka, BipulThe present investigation was carried out with the objectives to compute morphometric parameters of the drainage streams of Subansiri river basin and to evaluate soil erosion status in the basin area. The Subansiri watershed is located in the Lakhimpur district which is part of the North Bank Plains of Assam. The studied watershed encompasses 118.67 sq. km area and it lies between 94007’ E to 94018’ E Longitude and 27021’ N to 27036’ N Latitude with the elevation ranging from 86 to 124 m. Based on total variation in satellite data three distinct physiographic units of the studied watershed were delineated which includes: piedmont plain (29.75 sq. km), alluvial plain (63.05 sq. km) and flood plain (25.87 sq. km). The morphometric parameters were evaluated through measurement of linear, areal and relief aspects. The 1st, 2nd, 3rd and 4th order streams had stream numbers of 24, 5, 2 and 2, respectively. The mean bifurcation ratio for the studied area was evaluated to be 2.77. The areal aspects like circulatory ratio (0.70), elongation ratio (0.50), form factor (0.20) and shape factor (5.09) were estimated and the estimated value indicated elongated shape of the watershed. The computed relief aspects viz. relief ratio (0.0015), ruggedness number (0.05) and relative relief (0.082) indicated higher infiltration and lower runoff. Sixty surface soil samples (0-15 cm) along with equal no. of core samples representing all the three physiographic units were collected using handheld GPS of Garmin Etrex 20. The surface as well as core samples were analyzed for various physico-chemical properties. The texture of the studied soils varied from loamy sand to silty clay loam, sandy loam being dominant. There was a decreasing trend of total sand as well as an increasing trend of silt and clay from piedmont plain to flood plain. The bulk density, particle density and porosity of soils of the studied watershed area ranged from 1.01 to 1.61 Mg m-3, 2.19 to 2.88 Mg m-3 and 30.29 to 61.85 %, respectively. The hydraulic conductivity of the soils varied from 0.44 to 5.86 cm hr-1, while the water holding capacity ranged between 5.65 to 49.53 %. The field capacity, permanent wilting point and the available water content varied from 8.03 to 36.46 %, 2.65 to 14.98 % and 0.54 to 24.57 %. Among the physiographic units the piedmont plain soils recorded the highest value of hydraulic conductivity and flood plain showed the highest values of water holding capacity, field capacity, permanent wilting point and available water. The value of macro aggregates, micro aggregates and mean weight diameter of the studied soils varied from 20.20 to 79.54 %, 20.46 to 79.80 % and 1.13 to 3.91 mm, respectively. The pH of the studied soils was extremely acidic (4.15) to slightly acidic (6.69). The organic matter content of the soils ranged between low (5.38 g kg-1) to high (27.83 g kg-1). The available nitrogen, available phosphorus and available potassium content 10 varied from low to medium (137.98 to 464.13 kg ha-1), low to medium (15.96 to 55.25 kg ha-1) and low to medium (35.63 to 331.45 kg ha-1), respectively. Based on the estimated values of soil physico-chemical properties, various soil erodibility indices were computed. In the studied soils, the value of silt/clay ratio, clay ratio and modified clay ratio varied from 0.33 to 4.40, 1.46 to 13.25 and 1.36 to 11.73, respectively. The critical level of soil organic matter of all the studied soils was less than 5 per cent which indicated their vulnerability to soil erosion. The dispersion ratio in the studied soils varied from 0.05 to 0.42 with a mean value 0.26. The values of erosion ratio and erosion index were found to be varying between 0.01 to 0.48 and 0.02 to 0.62, respectively. It was observed that 80.59 sq. km (67.91 %) area had dispersion ratio value more than 0.15 which could be considered as erodible. Nearly 51.64 sq. km (43.52 %) area of the watershed had erosion ratio values more than 0.10 indicating their susceptibility to erosion. The erosion index values were more than 0.18 in about 44.51 sq. km (37.51 %) area. The soil loss of the studied area varied from very slight to very severe (0.87 to 67.95 t ha-1 yr-1) with an average value of 12.38 t ha-1 yr-1. The soil loss showed a significant positive correlation with very fine sand (r = 0.402**) and elevation (r = 0.509**). The soil loss exhibited positive correlation with various erodibility indices viz., silty/clay ratio (r = 0.159), clay ratio (r = 0.251), modified clay ratio (r = 0.249). However, the significant positive correlation of soil loss was noticed with dispersion ratio (r = 0.633**), erosion ratio (r = 0.405**) and erosion index (r = 0.502**). The soil loss along with dispersion ratio, erosion ratio and erosion index exhibited decreasing trend from the piedmont plain to flood plain.ThesisItem Open Access MORPHOMETRIC EVALUATION AND SOIL LOSS ESTIMATION OF A TRANSECT OF SUBANSIRI WATERSHED IN LAKHIMPUR DISTRICT OF ASSAM(AAU, Jorhat, 2020-08) KISHORE, KAMAL; Deka, BipulThe present investigation was carried out with the objectives to compute morphometric parameters of the drainage streams of Subansiri river basin and to evaluate soil erosion status in the basin area. The Subansiri watershed is located in the Lakhimpur district which is part of the North Bank Plains of Assam. The studied watershed encompasses 118.67 sq. km area and it lies between 94007’ E to 94018’ E Longitude and 27021’ N to 27036’ N Latitude with the elevation ranging from 86 to 124 m. Based on total variation in satellite data three distinct physiographic units of the studied watershed were delineated which includes: piedmont plain (29.75 sq. km), alluvial plain (63.05 sq. km) and flood plain (25.87 sq. km). The morphometric parameters were evaluated through measurement of linear, areal and relief aspects. The 1st, 2nd, 3rd and 4th order streams had stream numbers of 24, 5, 2 and 2, respectively. The mean bifurcation ratio for the studied area was evaluated to be 2.77. The areal aspects like circulatory ratio (0.70), elongation ratio (0.50), form factor (0.20) and shape factor (5.09) were estimated and the estimated value indicated elongated shape of the watershed. The computed relief aspects viz. relief ratio (0.0015), ruggedness number (0.05) and relative relief (0.082) indicated higher infiltration and lower runoff. Sixty surface soil samples (0-15 cm) along with equal no. of core samples representing all the three physiographic units were collected using handheld GPS of Garmin Etrex 20. The surface as well as core samples were analyzed for various physico-chemical properties. The texture of the studied soils varied from loamy sand to silty clay loam, sandy loam being dominant. There was a decreasing trend of total sand as well as an increasing trend of silt and clay from piedmont plain to flood plain. The bulk density, particle density and porosity of soils of the studied watershed area ranged from 1.01 to 1.61 Mg m-3, 2.19 to 2.88 Mg m-3 and 30.29 to 61.85 %, respectively. The hydraulic conductivity of the soils varied from 0.44 to 5.86 cm hr-1, while the water holding capacity ranged between 5.65 to 49.53 %. The field capacity, permanent wilting point and the available water content varied from 8.03 to 36.46 %, 2.65 to 14.98 % and 0.54 to 24.57 %. Among the physiographic units the piedmont plain soils recorded the highest value of hydraulic conductivity and flood plain showed the highest values of water holding capacity, field capacity, permanent wilting point and available water. The value of macro aggregates, micro aggregates and mean weight diameter of the studied soils varied from 20.20 to 79.54 %, 20.46 to 79.80 % and 1.13 to 3.91 mm, respectively. The pH of the studied soils was extremely acidic (4.15) to slightly acidic (6.69). The organic matter content of the soils ranged between low (5.38 g kg-1) to high (27.83 g kg-1). The available nitrogen, available phosphorus and available potassium content 10 varied from low to medium (137.98 to 464.13 kg ha-1), low to medium (15.96 to 55.25 kg ha-1) and low to medium (35.63 to 331.45 kg ha-1), respectively. Based on the estimated values of soil physico-chemical properties, various soil erodibility indices were computed. In the studied soils, the value of silt/clay ratio, clay ratio and modified clay ratio varied from 0.33 to 4.40, 1.46 to 13.25 and 1.36 to 11.73, respectively. The critical level of soil organic matter of all the studied soils was less than 5 per cent which indicated their vulnerability to soil erosion. The dispersion ratio in the studied soils varied from 0.05 to 0.42 with a mean value 0.26. The values of erosion ratio and erosion index were found to be varying between 0.01 to 0.48 and 0.02 to 0.62, respectively. It was observed that 80.59 sq. km (67.91 %) area had dispersion ratio value more than 0.15 which could be considered as erodible. Nearly 51.64 sq. km (43.52 %) area of the watershed had erosion ratio values more than 0.10 indicating their susceptibility to erosion. The erosion index values were more than 0.18 in about 44.51 sq. km (37.51 %) area. The soil loss of the studied area varied from very slight to very severe (0.87 to 67.95 t ha-1 yr-1) with an average value of 12.38 t ha-1 yr-1. The soil loss showed a significant positive correlation with very fine sand (r = 0.402**) and elevation (r = 0.509**). The soil loss exhibited positive correlation with various erodibility indices viz., silty/clay ratio (r = 0.159), clay ratio (r = 0.251), modified clay ratio (r = 0.249). However, the significant positive correlation of soil loss was noticed with dispersion ratio (r = 0.633**), erosion ratio (r = 0.405**) and erosion index (r = 0.502**). The soil loss along with dispersion ratio, erosion ratio and erosion index exhibited decreasing trend from the piedmont plain to flood plain.ThesisItem Open Access DISTRIBUTION OF MICRONUTRIENTS UNDER DIFFERENT LAND USES IN SOILS OF GOLAGHAT DISTRICT OF ASSAM(AAU, Jorhat, 2020-09) Barala, Jatiprasad; Basumatary, AnjaliAn investigation was carried out to study the depth-distribution of available micronutrients and their relationship with soil physico-chemical properties in soils of Golaghat district of Assam. Soil samples were collected at 0-20 cm, 20-40 cm, 40-60 cm, 60-80 cm and 80-100 cm depth under five land uses viz. rice, vegetable, sugarcane, bamboo and tea. Results indicated that sand, silt and clay content of the soils showed a significant variation among depths. The highest content of sand (59.53%), silt (51.13%) and clay (43.17%) were found at 80-100 cm, 20-40 cm and 80-100 cm under bamboo, vegetables and sugarcane land use, respectively. The soils were very strongly to medium acidic in reaction with a pH range of 4.70 to 5.73 and significantly the highest value of pH was recorded at 80-100 cm under all land uses. Organic carbon content of the studied soils was found higher in surface layer and decreased significantly with increasing soil depths. The significantly highest (13.27 g kg-1) and lowest content of organic carbon (1.47 g kg-1) in soil were observed under tea and bamboo land use, respectively. The exchangeable Ca2+, Mg2+, Na+ and K+ content was higher in soils of rice as compared to other land uses. The significantly highest and lowest mean values of both cation exchange capacity and per cent base saturation were observed under rice and bamboo land use, respectively. The content of available micronutrients showed a significant variation among different depth sunder different land uses. The content of available micronutrients was higher in surface layers and decreased with depths. The value of DTPA-extractable Fe, Mn, Zn and Cu content of the studied soils ranged from 10.28 to 80.28, 2.02 to 29.18, 0.08 to 0.77 and 0.12 to 1.76 mg kg-1, respectively under different land uses indicating the sufficiency of Fe, Mn and Cu. Content of DTPA- Zn was sufficient at 0-20 cm depth under rice and tea whereas deficiency was observed at lower depths in all the land uses. Among the land uses, surface layer of rice land use recorded significantly the highest concentration of DTPA-Fe, Mn, Zn and Cu as compared to other land uses. Significantly the highest content of boron was exhibited at surface layer in all the land uses and significantly the highest content of HWS-B (0.58 mg kg-1) was observed at 0-20 cm depth under tea land use. Most of the soils were found below critical limit except sugarcane and tea at 0-20 cm depth. DTPA-extractable micronutrients and HWS-B correlated positively and significantly with soil organic carbon, cation exchange capacity and per cent clay but negatively and significantly with soil pH. Clay showed a significant and positive correlation with DTPA-Mn, DTPA-Zn and DTPA -Cu. Step-down multiple regression analysis revealed that organic carbon, pH and clay were the dominant factors accounting for maximum variability in available micronutrient contents.
