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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 DISTRIBUTION OF PEDOGENIC IRON AND ALUMINIUM IN RELATION TO SOIL ACIDITY COMPONENTS UNDER DIFFERENT LAND USES IN GOLAGHAT DISTRICT OF ASSAM(AAU, Jorhat, 2018) Kalita, Pallabi; Dutta, MaramiAn investigation was carried out to study the pedogenic distribution of Fe and Al, the soil acidity components and to assess the relationship of pedogenic Fe and Al with soil acidity components under different land uses in Golaghat district of Assam. Five pedons were selected representing five land uses viz., Forest cover (P1), Paddy cultivation (P2), Tea plantation (P3), Bamboo plantation (P4) and Vegetable cultivation (P5) from Nambor Doigrung Reserve Forest, Borjan, Doria, Dergaon and Danichapori respectively. The dominant hue of soil colour was 10YR. Value ranged from 4 to 7 and chroma ranged from 1 to 6. Texture varied from sandy loam to clay loam in the surface and loam to clay in the sub-surface horizons. The structure of the soils varied from massive in the surface to sub-angular blocky to angular blocky in the subsurface. The clay content and bulk density increased with soil depth. The highest amount of organic carbon was recorded in A horizon of forest soil (P1) with 2.2 per cent. The pH were in acidic range in all the pedons and in all the cases ΔpH (pHKCl – pHH20) was negative. Among the exchangeable cations Ca2+ was the dominant followed by Mg²⁺, Na⁺ and K⁺. CEC ranged from 7.5 to 10.8 in the surface and 5.8 to 15.9 cmol (p⁺) kg⁻¹ in the sub-surface horizons. The percent base saturation generally tended to increase with depth with some exceptions in P1. Soils were classified as Typic Dystrudepts (P1, P3 and P4), Oxyaquic Hapludalfs (P2) and Aquic Udifluvents (P5). Dithionite extractable Fe (Fed) and Al (Ald) constituted the highest amount among the pedogenic iron and aluminium. Fed tended to increase with soil depth with few exceptions. On the weighted average, paddy soil (P1) recorded the highest Fed. Oxalate extractable iron (Feo), amorphous inorganic iron (Feo – Fep) was irregularly distributed in all the pedons. On the weighted average vegetable soil (P5) and paddy soil (P2) recorded highest (Feo) and (Feo – Fep) respectively. The distribution of (Fed – Feo) was irregular in all the pedons except P1. On the weighted average forest soil (P1) recorded the highest (Fed – Feo). The surface horizons recorded comparatively higher amount of pyrophosphate extractable iron (Fep) than the subsurface horizons in all the pedons. The amount of KCl extractable iron (FeKCl) was low which ranged from 0.001 to 0.002 per cent in all the pedons. The ammonium acetate extractable iron (FeNH4OAc) was below detectable limits in all the pedons. On the weighted average, Paddy soil (P2) recorded the highest dithionite extractable aluminium (Ald). Oxalate extractable aluminium (Alo), crystalline form of aluminium (Ald – Alo) and amorphous inorganic aluminium (Alo – Alp) followed inconsistent trend with soil depth whereas pyrophosphate extractable aluminium (Alp) decreased with soil depth. Bamboo soil (P4) recorded the highest Alo, bamboo soil (P4) and vegetable soil (P5) recorded highest Alp. Bamboo soil (P4) recorded highest (Alo – Alp) and forest soil (P1) recorded highest (Ald – Alo). The amount of ammonium acetate extractable aluminium (AlNH40AC) at pH 4.8 was low but was higher than that extracted by KCl solution. Profile weighted mean of forms of acidity under various land uses depicted that the paddy soil (P2) exhibited maximum extractable, non-exchangeable and hydrolytic acidity, tea soil (P3) exhibited maximum total acidity, exch. H+, exch. Al3+ and exchange acidity and bamboo soil (P4) exhibited maximum pH dependent and total potential acidity. It was observed that the soils under forest cover (P1) and vegetable cultivation (P5) exhibited lower acidity compared to other land uses in the present study. Principal component analysis of the 27 soil characters revealed that different forms of Fe and Al contributed towards development of soil acidity irrespective of land use. Among the physico-chemical parameters clay contributed positively and significantly and pH (pHH2O and pHKCl) contributed negatively and significantly towards soil acidity.ThesisItem Open Access PEDOGENIC CHARACTERIZATION OF PADDY AND ASSOCIATED NON-PADDY SOILS OF ASSAM(AAU, Jorhat, 2018) Mohanty, Shraddha; Karmakar, Rajendra MohanAn investigation was carried out to study the morphological, physical and chemical characteristics, clay-organic carbon complexes and pedogenic distribution of iron, manganese and aluminium in clay fraction of paddy and associated non-paddy soils of Assam. Four districts viz., Golaghat, Jorhat, Sivasagar and Dibrugarh in the Upper Brahmaputra valley of Assam were selected for the present study. Eight soil profiles four each from mono-cropped paddy and associated non-paddy areas were collected. Horizon-wise soil samples were analyzed for important soil properties and clay-organic carbon complexes and different forms of Fe, Al, Mn in clay fraction using standard procedures. Soil colour varied from dark gray to brownish yellow. Yellow (10YR 6/8) to light red (2.5YR 6/8) mottles were observed in the subsurface horizons of the soils. Texture of the soils ranged from loamy sand to clay and structure varied from massive to subangular blocky. Sand, silt and clay contents varied from 11.3-49.0, 21.5-50.8 and 26.2-56.9 per cent in paddy and 23.3-65.4, 11.4-42.9 and 14.4-44.4 per cent in non-paddy soils respectively. Organic carbon content in soil varied from 2.0-12.0 and 0.5-10.0 g kg-1 in paddy and non-paddy soils respectively. Bulk density of soils increased with soil depth, pH of the soils varied from 4.4-6.0 and EC was found to be low (0.11-0.20 dSm-1). CEC of soil varied from 7.5-14.1 cmol (p+) kg-1 in paddy and 5.1-12.7 cmol (p+) kg-1 in non-paddy soils having dominance of exch. Ca++ followed by Mg++, Na+ and K+. Base saturation of the soil was low (32.3 to 57.5%). Soils were classified as: Typic Epiaqualfs (P1), Aeric Epiaqualfs (NP1, P2, P3, NP3, P4), Ultic Hapludalfs (NP2) and Typic Dystrudepts (NP4). Clay-organic carbon complex (OCclay) varied from 2.41-15.5 g kg-1 in paddy soils and 0.71-13.80 g kg-1 in non-paddy soils. Results showed that OCclay constituted 37.18-65.60% of SOC in paddy soils and 31.60-54.62% of SOC in non-paddy soils. Humus C (CH-clay), humin C (CHN-clay) in the clay fraction was found to be higher in non-paddy soils, whereas humic acid C (CHA-clay) and fulvic acid C (CFA-clay) in clay fraction was higher in paddy soils than their counter parts. CHA-clay/CFA-clay ratio was observed to be less than 1 indicating dominance of fulvic acid in the clay-organic carbon complexes. 25 Total (Fet), dithionite extractable (Fed), pyrophosphate extractable iron (Fep) and manganese in clay fraction were slightly higher in non-paddy soils as compared to paddy soils whereas oxalate extractable iron and manganese showed a reverse trend. Fed formed major portion of total iron content in clay fraction (Fet) followed by Feo and Fep in both paddy and non-paddy soils. Crystalline iron oxide (Fed-Feo) and silicate iron (Fet-Fed) in clay fraction was found to be higher in non-paddy soils while amorphous inorganic form of iron (Feo-Fep) showed the reverse trend. Different forms of Mn showed similar trend as that of different forms of iron in clay fraction of both paddy and associated non-paddy soils. Total Al (Alt), dithionite extractable Al (Ald) and oxalate extractable Al (Alo) in clay fraction were slightly higher in paddy soils as compared to non-paddy soils whereas pyrophosphate extractable Al (Alp) showed a reverse trend. Ald formed major portion of total Al content in clay fraction (Alt) followed by Alp and Alo in both paddy and non-paddy soils. Crystalline Al oxide (Ald-Alo), amorphous inorganic Al (Alo-Alp) and silicate Al (Alt-Ald) in clay fraction was found to be higher in paddy soils than non-paddy soils. In the present investigation, variation in morphological, physical and chemical characteristics of soils, clay organic carbon fractions, distribution of various forms of Fe, Mn and Al in clay fraction were observed in the paddy and associated non-paddy soils of Assam. Low amount of sand and high amount of clay in paddy soils as compared to non-paddy soils indicate more intense weathering in paddy soils due to anthropogenic factors and agro-hydrological regimes. Most of the paddy soils exhibited aquic characteristics leading to process of gleization. Formation of more amounts of clay-organic complexes was also observed in the paddy soils. Further studies are needed using modern tools (SEM, IR, X-ray etc.) for detailed pedogenesis and mechanisms in clay-organic complex formation in paddy and associated non-paddy soils of Assam.ThesisItem Open Access ALUMINIUM AND PHOSPHATE POTENTIAL IN ACID SOILS OF ASSAM(AAU, Jorhat, 2018) Borah, Supriya; Bhattacharyya, DevajitThe study was carried out to investigate the “Aluminium and Phosphate Potential in Acid soils of Assam”, with the objectives 1) Determine different form of aluminium and phosphorus in Upper Brahmaputra Valley Zone (UBVZ) of Assam and 2) Determine aluminium and phosphate potential in soils of UBVZ of Assam. For this study twenty (20) surface (0-15 cm) soil samples were collected from Sivasagar, Golaghat and Majuli district of Assam. The soils were analyzed for different parameters pertaining to this investigation following standard procedures and laboratory protocols. The soils were varied widely in texture (sandy clay loam to clay), clay content (13 - 40%), pH (H2O) (4.02-7.49), pH (KCl) (3.10 to 6.89), OC (0.59-2.85%), CEC (6.75 to 12 cmol (p+) kg-1), free oxides of iron (3.78 to 1.09%) and aluminium (1.17 to 0.32%), lime potential (3.04 -5.85). The results on forms of acidity revealed that TPA (7.05 cmol (p+) kg-1) was the most dominant form of acidity in soils UBVZ of Assam followed by PDA (5.13 cmol (p+) kg-1), Ext.A (3.16 cmol (p+) kg-1), TA (1.92 cmol (p+) kg-1) = Ex.A (1.92 cmol (p+) kg-1) and Non Ex.A (1.22 cmol (p+) kg-1). Among the forms of Al, the CBD extractable aluminium (Ald) was found to be the most dominant followed by oxalate extractable Al (Alo), weakly organically bound Al (Alw), totally organically bound Al (Alp) and exchangeable Al (AlKCl), with mean values 0.38,0.22, 0.09, 0.02 and 0.01per cent, respectively. The amorphous form of aluminium showed dominance over the crystalline form of aluminium. The Organic phosphorus of the soils ranged from 164.68 to 345.62 mg kg-1. Different inorganic P fractions of the soils were found in the order: Fe-P (68.2-20.4 mg kg-1) > Al-P (42.9-19.7 mg kg-1) > Occl-P (20-11 mg kg-1)>Ca-P (10.2-17.6 mg kg-1) > Re-P (15.6-9.2 mg kg-1)> Sal-P (2.3-10.2 mg kg-1). The percent release Al (%RelAl) decrease with increase in added Al irrespective of the soil studied. The highest and lowest %RelAl was observed in soil S4 of Sivasagar district and soil M3 of Majuli district, respectively. The decrease in %AdsP was ranged from 97.6 to 7.00 per cent in soils of UBVZ of Assam when addition of P was ranged from 1 to 5 mg l-1. The highest % AdsP was found in soil S1 of Sibsagar district, with a mean value of 97.11 per cent. The lowest mean % AdsP (15.98 %) was found in soil UM6 of Majuli. P released was observed at equilibrium solution of soil S8 of Sivsagar district and soil M3 of Majuli district at the lowest concentration of add P i.e. 1 mg l-1. In soil UM5 and UM6 of Majuli district % RelP was observed from 1 to 3 mg l-1 of add P. In all these soils % RelP was decreased with increased in addition of P. The mean value of % RelP in soils of UBVZ ranged from 20.64 to 30.89 per cent. The soil UM5 (24.32) of Majuli district had the highest aluminium potential and the same was the lowest in soil S4 (16.08) of Sivsagar district. Equilibrium aluminium potential (EAP) of the soils showed very high significant positive correlation with pH (H2O) and pH (KCl) (r=0.865** and r=0.735**) and very significant negative correlation with oxides of iron and aluminium (r=-0.819** and r=-0.850**). EAP of the soils also had negative correlation with all forms of acidity and exchangeable aluminium. The highest phosphate potential was observed in soil S1 (5.30) of Sivsagar district while lowest was observed in soil UM5 (0.70) of Majuli district. In these soils equilibrium phosphate potential (EPP) had a significant negative correlation with soil pH (H2O) (r=-0.956**) and pH (KCl) (r=-0.858**), and significant positive correlation with oxides of iron (r=0.938**) and oxides of aluminium (r=0.963**). Significant positive relationship of EPP was also observed with all forms of acidity except non exchangeable acidity. While a significant positive correlation was observed with Fe-P (r=0.791**), Al-P (r=0.733**), Occl-P (r=0.930**) and RS-P (r=0.500*). However, EPP of the soils had significant negative relationship with Org-P (r=-0.560**), Ca-P (r=-0.849**) and Sal-P (r=0.857**). The correlation of EPP with EAP and lime potential (LP) of the soils was significant and negative (r=-0.969** and r=-0.872**), respectively. In soils of UBVZ of Assam if EAP and LP were high the equilibrium phosphate potential will be low indicating higher availability of phosphorus, as increase of LP and EAP also increase the pH of the soils. Therefore, liming and addition of organic matter might be considered good management practices for these acid soils to increase the pH as well as to increase the Phosphorus availability.ThesisItem Open Access FORMULATION OF LIQUID RHIZOBIAL BIOFERTILIZER AND ITS VALIDATION(AAU, Jorhat, 2018) Bharali, Happy; Baruah, RajenThe present study on “Formulation of liquid rhizobial biofertilizer and its validation” was carried out in the laboratory of the Biofertilizer Production Unit, Department of Soil Science, Assam Agricultural University, Jorhat during 2017-18. The objective of this investigation was to determine the shelf-life of the liquid formulation, to study the nodulation pattern and establishment of added rhizobia in specific host legumes and to ascertain the validation of the effective liquid formulation on pea, green gram and black gram. The experiment was laid in a Completely Randomised Block Design. The individual strains of greengram(Rhiz-10) and blackgram(Rhiz-13) was diluted to different formulations of 25, 50, 75 and 100 per cent and shelf-life was examined in comparision with a solid substrate at 0, 30, 60, 90 and 120 days of incubation. Results showed that viable population of rhizobia could be maintained with different formulations even upto 120 days. Whereas, in solid substrate the viable population started decreasing more, as days of incubation increased irrespective of pulse crops . The colony forming unit in 100 per cent liquid formulation ranged from 1.2 to 3.2x108 cfu/ml in greengram and 1.7 to 2.4x108 cfu/ml in blackgram from 0 to 60 days of incubation. Nodulation pattern was studied in terms of infectivity test for three crops viz. pea, greengram and blackgram under sterile condition using Gibson tube method. The three rhizobial strains (Rhiz-25, Rhiz-10 and Rhiz-13) of different concentrations of 25, 50, 75 and 100 per cent was prepared and inoculated in tubes and some tubes were kept as control. At 20th day of inoculation, nodule number, nodule dry weight and establishment (cfu/nodule) was found to be highest for all the three crops on application of 100 per cent liquid formulation. The establishment of rhizobia per nodule at 100 per cent liquid formulation for pea, green gram and blackgram was recorded to be 5.6, 7.3 and 5.0x103 cfu/nodule respectively. For validation, a pot culture study was conducted using pulses like pea, greengram and blackgram under unsterile condition with respective rhizobial formulation of 50 and 100 per cent concentration. The replicated plants were grown for 60 days and thereafter harvested. The results showed that nodulation pattern (nodule number and dry weight), and yield parameters increased significantly over uninoculated control at 50 and 100 per cent formulation. Rhizobia got well established in treated pots. Further, enzyme activities of the soil with respect to inoculated crops also increased indicating enhanced rhizobial activity. The numerical data on yield recorded for pea, greeengram and blackgram were 25, 18 and 12 pods per plant at 100 per cent rhizobial formulation. Similarly, enzyme activities also increased from 26.66 to 35.52 μg TPF g-1 24 h-1 DHA, 1.63 to 2.57 μg fluorescein g-1 30 mins-1 FDA and 12.12 to 16.58 μg p-nitrophenol/gm/hr PMEase for soil grown with pea at 100 per cent rhizobial formulation and similar trend of result also showed in soil planted with greengram and blackgram.ThesisItem Open Access LAND EVALUATION FOR CROP INTENSIFICATION IN BUMNOI-MORNOI WATERSHED OF KOKRAJHAR DISTRICT OF ASSAM USING REMOTE SENSING AND GIS TECHIQUES(AAU, Jorhat, 2017-07) Basumatary, Danswrang; Dutta, MaramiThe present study was undertaken in Bumnoi-mornoi watershed of Kokrajhar district of Assam in order to characterize and prepare soil resource maps, to study soil site suitability and to find out the related constraints for crop production. Altogether six profiles and twenty two surface samples were collected from two different physiographic units viz., alluvial plain and flood plain. The samples were analyzed for various morphological and physic-chemical properties. The dominant hue of soil colour was 10YR, except in sub surface C horizon of P1 (AP) where it was 7.5YR. Colour value ranged from 3 to 6 and chroma from 1 to 6. Yellowish red (2.5YR 4/6) to reddish yellow (7.5YR 7/6) mottles were observed in the soils. Wide variations were observed in soil textural class varying from sand to clay loam. The structure of the soil varied from medium, weak to moderate sub angular blocky at the surface to very fine to medium, week to moderate sub angular blocky, massive and single grain structure. Organic matter content in the soil varied from 0.07 to 3.13 g kg-1, the highest being observed in the surface Ap horizon of P3. Soil pH varied from 4.7 to 6.2. Sand, silt and clay contents in these soils varied from 23.3 to 89.2, 9.9 to 60, and 1.8 to 22.1 per cent, respectively. Among the exchangeable cations, Ca2+ was the dominant cation followed by Mg2+, Na+ and K+. CEC of the soils varied from 3.5 to 10.2 cmol (p+) kg-1. Available N varied from 13.44 to 448.0 kg ha-1, available P2O5 varied from 0.92 to 55.70 kg ha-1 and available K2O varied from 137.2 to 451.0 kg ha-1, respectively. The studied soils were classified as Aquic Dystrudepts (P1), Oxyaquic Dystrudepts (P2, P4), Typic Dystrudepts (P3), Aquic Udorthents (P5) and Fluvaquentic Epiaquepts (P6). The productivity of the soils for crop production varied from poor to good in alluvial plain, and poor to average in flood plain. Potential productivity varied from average to good in alluvial plain and flood plain, respectively. The co-efficient of improvement (CI) values indicated that the productivity of the alluvial plain and flood plain soils can be increased to maximum extend of 2.22 to 1.88, respectively. Soil site suitability assessment showed that the soils were moderately suitable (S2) to permanently unsuitable (N2) for Sali rice, Ahu rice, Potato and Maize. Soils were found to be very suitable (S1) to permanently not suitable (N2) for Banana. For pineapple, the soils were found to be very suitable (S1) to moderately suitable (S3). Various thematic and soil site suitability maps along with potential productivity maps of the study area were prepared using remote sensing and GIS techniques.ThesisItem Open Access DISSOLVED ORGANIC MATTER AND SOIL ENZYME ACTIVITY IN ORGANIC CULTIVATION OF RICE(AAU, Jorhat, 2017-07) Buragohain, Pubali; Nath, DhrubaJyotiThe dissolved organic carbon (DOC), dissolved organic nitrogen (DON), reducing sugars(hexose and pentose), soluble phenols, protein, amino acids,key enzymes [arylsulfatase(ARS), phosphomonoesterase (PME), fluorescein di-acetate (FDA) β-glucosidaseand urease] contained indissolved organic matter (DOM) and biodegradability of DOM were assessed as influenced by application of organic inputs in organic rice (variety: Joha)after five years of experiment. Two extractantsviz:1.0MKCl(salt extractable organic matter, SEOM) and 5.0mM CaCl2(water extractable organic matter, WEOM) were used for extraction of DOM from the rhizosphere soils. The results indicated the significant variations of DOM under the organic inputs. Significantly highest DOC of 83.41(mg/kg) and 31.32(mg/kg) were obtained by the extractants SEOM and WEOM on application of enriched compost (EC) (@5t/ha) and compost(5t/ha) respectively. Significantly highest DON of 54.33 and 47.54(mg/kg) were obtained in the extractant SEOM and WEOM under the application of EC@5t/ha and 2.5t/ha respectively. The phenol, protein, amino acids and reducing sugars were also exhibited the significant variation under different organic inputs following the utilization of two extractants. Among the organic inputs, EC @ 5.0t/ha, @2.5t/ha and compost @5.0t/ha with biofertilizer consortium contributed significantly higher amount of enzymes in DOM. Application of EC either @ 5.0t/ha or @2.5t/ha continuously for five years could resulted significantly highest amount of PME, FDA and ARS activity while application of compost @5.0t/ha with or without biofertilizers could resulted higher content of urease and β-glucosidase activity respectively. The total organic carbon (TOC) and total nitrogen (TN) were significantly highest (12.53 g/kg and 8.60g/kg respectively) in soil under the application of EC @5.0t/ha while soil organic carbon (SOC), was significantly highest (10.60g/kg) under the application of compost@5t/ha. Likewise the fractions (F1, F2, F3 and F4) of TOC were influenced significantly by different organic inputs. The correlation matrix illustrated the significant correlation between the two extractant for ARS (0.787**),PME (0.490*) ,β-glucosidase (606**),hexose (756**), protein (0.736**) and biodegradable DOM(0.595**). DON of DOM also established significant correlations in between the two extractant but in a different way. The SOC, TOC, fraction 1 and fraction 2 of TOC illustrated significant correlation with the DOC ofSEOM while TN could show the significant correlations with DON of both the extractants. However, varied significant correlations between the SOC, TOC, fractions of TOC and TN with different components of DOM were observed under the two extractants.The biodegradability of DOM were also significantly influenced by DOC, DON,SOC, fractions of TOC, TOC and TN at varying degree under the two extractants. The favorable soil environment encouraged due to successive application of organic inputs for five years eventually reflected the improvement in rice (aromatic Joha) yield by 21.37-33.76% over unfertilized control.ThesisItem Open Access SOIL AVAILABLE PHOSPHORUS PEDOTRANSFER FUNCTION FOR ACIDIC SOILS OF CENTRAL BRAHMAPUTRA VALLEY ZONE OF ASSAM(AAU, Jorhat, 2019-07) Saikia, Bishnu Jyoti; Borkakati, KabindraThe study on “Soil available phosphorus pedotransfer function for acidic soils of Central Brahmaputra Valley Zone of Assam” was carried out with the objectives 1) to develop a soil available-P-pH pedotransfer function for acidic soils, 2) to verify the developed model with laboratory database and 3) to evaluate the relationship of available P with their various forms. In total 220 surface soil samples (0-15cm) were collected from the three districts of CBVZ of Assam viz. Nagaon (n=120), Morigaon (n=50) and Hojai (n=50). Physico-chemical properties for all the samples were determined by using standard methods. The pH, available P, OC and CEC of the collected soil samples were ranged from 3.45 to 6.50, 18.00 to 55.47 kg P2O5 ha-1, 0.32 to 1.34 per cent and 4.38 to 8.70 c mol (p+) kg -1, respectively. The average values of mechanical separates of the soils were found to be 35.82, 22.85 and 41.33 % for sand, silt and clay, respectively and the texture of these soils varied from sandy to clayey. Out of the 220 samples, 44 samples were selected on the basis of variation in soil texture for developing a pedotransfer function. The average values of mechanical separates of later consisted of 35.82 %, 22.85 % and 41.33 % sand, silt and clay, respectively. The range of pH, OC, CEC, Ald, Fed and available P ranged from 3.85 to 6.40, 0.32 to 1.34%, 4.90 to 9.40 [c mol (p+) kg -1], 0.34 to 1.62%, 0.61 to 1.84% and 20.11 to 55.47 P2O5 kg ha-1, respectively. A pedotransfer function (PTF) for predicting soil available P from soil pH data was developed and soil available P (AP) was estimated as a function of soil pH. The developed function is : Available P = -25.69+12.07*pH. The predicted P (i.e. soil available P predicted from the available P pedotransfer function) was compared with the soil available P estimated by laboratory test using the paired samples t-test and the Bland-Altman approach. The available P predicted by the soil available P pedotransfer function was found not to be significantly different from the soil available P determined by laboratory test (P >0.05). The mean difference between the soil available P-PTF and laboratory test was -0.004 kg ha-1 (95% confidence interval: -0.7699 and 0.7614 kg ha-1; P=1.00). The standard deviation of the soil available P differences was 2.518 kg P2O5 ha-1. More than 95% values of soil available phosphorus differences laid within the limits of agreement which in this case are -4.940 to 4.932 kg P2O5 ha-1. Thus, the pedotransfer function can be accepted as it also did not show any bias between the two methods calculated by Bland-Altman approach. Results revealed that the sequential occurrence of various inorganic P fractions followed the order: Fe-P > Al-P > organic-P > residual-P > Ca-P > saloid-P. The order of partial contribution of inorganic P fractions towards total inorganic P was Fe-P > Al-P > residual-P > Ca-P > saloid-P. Bray’s-I-P showed a significant positive correlation with OC (r= 0.742**), pH (r= 0.524**), CEC (r= 0.552**), clay (r= 0.508**), Ald (r= 0.464**), Fed (r= 0.519**) and significantly negative correlation with sand (r= - 0.407 **). Stepwise multiple regression analysis indicated that the highest contribution was impacted by Fe-P (38%) towards Bray’s-I-P whereas inclusion of res-P increased the variability to 48 per cent. All the P fractions jointly contributed 57 per cent towards the variability of available P. Step-wise multiple regression study showed the existence of dynamic equilibrium amongst different P fractions in the soils studied. Step wise multiple regression analysis indicated that the highest contribution was imparted by saloid-P (15%) towards predicted P while addition of Al-P contributed 22% towards predicted P. Inclusion of all the P fractions changed the variability to 37%. From the foregoing discussion, it can be concluded that the pedotransfer model can be accepted as because there was no bias between the two methods which is a pre-requisite according to Bland-Altman approach for both the methods to be in close agreement.
