Loading...
Theses
Browse
Search Results
ThesisItem Open Access GROWTH & YIELD OF TEA AND SOIL NUTRIENT AVAILABILITY AS INFLUENCED BY TEA – RUBBER CROPPING SYSTEM(2023) Borah, Rishika; Saikia, G.KTea is generally grown as a monoculture. However to augment farm income of small tea growers the concept of tea based cropping system where other crops are raised within a tea plantation is being tried. Two cropping systems- one with tea under conventional shade and the other with tea under intercrop situation were studied. The experiment was carried out in Experimental Garden for Plantation Crops, Department of Tea Husbandry and Technology, Assam Agricultural University, Jorhat during 2022. Effect of rubber on growth and yield of tea in tea based cropping system was studied along with the nutrient availability in the soil. Tea under conventional shade tree Albizzia chinensis gave highest yield when compared to tea under rubber plant’s shade as the uptake of nutrients was more. The light penetrating through the dense canopy of rubber is very low, which is a direct factor for lowered yield under rubber shade. Even the thickness of the tea stem, plucking point density, shoot weight, bush spread of tea was found to be highest in the tea- Albizzia chinensis plot. The nutrient uptake by the tea shoot was higher in the control plot due to proper penetration of light and adequate nutrients in the soil. Rubber tree shows increment in girth which is an important parameter for the rubber yield. For the growth and development of the rubber tree, canopy is also an important factor as it regulates the exchange of carbon. Tea under rubber shade was more prone to moisture stress due to higher rate of transpiration. The soil carbon content was found to higher in the tea-rubber intercropped plot due to faster rate of decomposition of leaf litters in a well shaded condition. The available NPK content was found to be higher in the intercropped plot due to releasing of nutrients by the tree to meet crop demands. The rubber plant had no adverse effect on the soil status but due to the dense canopy spread of the rubber interplanted with narrow spacing the light transmission is quite low which eventually effects the yield and growth of the tea plants.ThesisItem Open Access Molecular Characterization of Arsenic Oxidizing Bacteria from Hot Spots of Assam(2023) Nilakhi Dutta; Nath, Dhruba JyotiIn view of wide scale toxicity of Arsenic (As), development of a sustainable low cost As `detoxification technology is an urgent need of time. Bioremediation of As by microorganisms has been widely hailed because of their potential advantage in As transformation through oxidation, reduction, methylation and volatilization. As (III) oxidizing bacteria plays a key role in the biological conversion of highly toxic and mobile As(III) to less toxic As(V) in the environment and hence can be a potent candidate for bioremediation of As contamination. 44 georeferenced soil samples and 22 georeferenced water samples were collected from As contaminated hot spots of Jorhat, Darrang and Nagaon districts of Assam for isolation of As(III) oxidizing bacteria. A total of 52 As tolerant isolates (39 from soil and 13 from water samples) were obtained initially in nutrient agar(NA) media supplemented with 1mM As(III). Highest percentage recovery of As tolerant bacteria was observed in sample DS6 (56.02%) of Darrang district. Significant correlation (p ≤0.01) was established between percent recovery of As tolerant bacteria with total As content in soil and water samples. Following primary screening based on minimum inhibitory concentration (MIC) of As, 15 isolates that could tolerate upto 17.5 mM As(III) or above were selected for further studies. Morphological and biochemical characteristics of the selected As tolerant bacteria were studied. All the 15 isolates showed positive response to citrate utilization tests and negative for Indole, H2S production and Voges Proskauer test. The isolates also showed significant variation in carbon source utilization indicating diversity of organism to utilize different carbon sources. Antibitotic resistance profile of the isolates revealed that all the isolates showed resistance to penicillin. DS1al and DS13a showed resistance against 8 tested antibiotics. The growth of all isolates was found to be optimum at pH 7.2 and at temperature 300C ranging from 20 to 177 cfu mL-1 and 20 to 185 cfu mL-1 respectively. Study of growth pattern in terms of colony forming units (CFU) and optical density(OD) of the isolates at 0h, 24h, 48h and 72h interval showed higher reduction in growth in presence of As(III) compared to the presence of As(V). Heavy metal tolerance limit of the isolates ranged from NiCl2 (1-6 mM), CuSO4(1-7 mM), CoCl2 (0.1-1 mM), ZnSO4 (0.5-3 mM), HgCl2 (0.1-0.5 mM), Pb(NO3)2 (4-10 mM) and AgNo3 (0.5 mM). Ten isolates viz., DS1al, DS2a, DS5a, DS7am, DS8bm, DS11ama, DS13a, DS15a, DS17b and NS12c showed positive oxidation reaction in both AgNO3 and Microplate screening assay done to detect the As oxidizing isolates. Quantitative assessment of As oxidation using high performance liquid chromatography (HPLC) revealed that these isolates can transform As(III) to As(V) in the range of 46.53 -73.29 % in presence of 15.5 mM As(III). Highest oxidation efficiency is shown by isolate DS2a (73.29%) followed by NS12c (62.84%) and the lowest being in DS15a (46.53%). Overall, all these 10 selected isolates showed potential detoxification response against As. Scanning electron microscopy done for observation of invitro As bioaccumulation of the isolates revealed distinct changes in cellular morphology including decrease in cell length, increase in cell volume and typical dents in septal area. Taxonomic identity of the entire ten As oxidizing isolates revealed their close identity to Pseudomonas laurentiana, Glutamicibacter creatinolyticus, Providencia huaxiensis, Myroides profundi, Citrobacter tructae, Citrobacter murliniae, Bacillus pseudomycoides and three isolates identical to Lysinibacillus boronitolerans.ThesisItem Open Access Assessment of soil properties and carbon sequestration under fodder crop based systems(2023) Gogoi, Manjurima; Patgiri, Dilip KumarThe present investigation was carried out for assessment of soil physico-chemical and biological properties, distribution of different forms of soil carbon and contribution of different forms of soil carbon on soil aggregation under different fodder crop based system. Soil samples were collected from twenty three crop situations of three locations of Jorhat and Golaghat districts of Assam including virgin soils. Samples were collected as bulk soil samples, large core samples and mini core samples from 0–20, 20-40, 40-60, 60-80 and 80-100 cm soil depth from each plot under fodder crop and virgin soil. It was observed that soil physico- chemical and microbiological properties were greatly improved by continuous cultivation of fodder crops. The pH of soils under fodder crops down the depth were higher than those in virgin soils making these soils less acidic in reaction. Continuous cultivation of fodder crops increased the per cent organic carbon content of soil and it is high in case of napier than other fodder crops. Available nitrogen, phosphorus, potassium, calcium and magnesium contents increased due to continuous cultivation of fodder crops and continuous cultivation of napier grass as well as setaria showed high range of these nutrients than other fodder crops. Continuous cultivation of fodder crops increased hydraulic conductivity of soils and six years continuous cultivation of napier showed highest range of hydraulic conductivity of 0.119 cm sec-1 to 0.001 cm sec-1 with a mean value of 0.028 cm sec-1. Bulk density decreased due to continuous cultivation of fodder crops and continuous cultivation of setaria for six years showed lowest bulk density ranged from 0.93 Mg m-3 to 1.05 Mg m-3 with a mean value of 1.00 Mg m-3. Per cent available water content increased due to continuous cultivation of fodder crops and fourteen years continuous cultivation of napier showed highest range of available water content of 13.37% to 6.79% with a mean of 10.59%. Continuous cultivation of napier, setaria and congosignal showed higher soil aggregation and mean weight diameter than other fodder crops and virgin soil. The microbial biomass carbon, phosphomonoesterase activity and dehydrogenase activity of fodder crops was much higher than the virgin soils. The highest microbial biomass carbon range was found in case of fourteen years continuous cultivation of napier (769.3 μgm gm-1 to 96.6 μgm gm-1 with a mean of 388.3 μgm gm-1). Six years continuous cultivation of maize showed highest phosphomonoesterase activity (336.5 μgmgm-1hr-1 to 210.1 μgmgm-1hr-1 with a mean of 249.0 μgmgm-1hr-1) and five years continuous cultivation of hybrid napier showed highest dehydrogenase activity (22.94 μgmgm-1hr-1to 5.69 μgmgm-1hr-1with a mean of 15.82 μgmgm-1hr-1). The highest total organic carbon content wasfound in case of continuous cultivation of napier followed by continuous cultivation of setaria and it was higher in 20-40 cm layer of soil than in 0-20 cm layer. Six years continuous cultivation of napier showed highest range of soil carbon stock of 37.01 t ha-1 to 24.64 t ha-1 with a mean of 31.46 t ha-1. The oxidisable organic carbon decreased with the increase in soil depth down the profile anddue to high vegetative growth, continuous cultivation of napier or hybrid napier showed high oxidisable organic carbon in soils. Highest hot water extractable organic carbon was found in continuous cultivation of hybrid napier followed by setaria. The highest cold water extractable organic carbon content was found in six years continuous cultivation of cowpea. The highest range ofhumic acid and fulvic acid were found in continuous cultivation of napierfollowed by continuous cultivation of setaria.The very labile carbon and labile carbon also decreased down the profile with increase in soil depth and continuous cultivation of napier as well as setaria showed higher values than other fodder crops and virgin soils. Fourteen years continuous cultivation of napier showed highest very labile carbon (0.94% to 0.27% with a mean of 0.58%) and labile carbon (0.87% to 0.20% with a mean of 0.50%).The highest range of less labile carbon was found in six years continuous cultivation of napier (0.29% to 0.47% with a mean of 0.39%) which was high in lower soil depths than upper 0-20 cm soil layer. The non labile pool of carbon first increased and later decreased down the profile with increase in soil depth in both fodder crops and virgin soils. Significant positive correlation was observed for labile carbon with very labile carbon; cold water extractable organic carbon with hot water extractable organic carbon; humic acid with very labile carbon, labile carbon and hot water extractable organic carbon; fulvic acid with very labile carbon, labile carbon ,hot water extractable organic carbon, cold water extractable organic carbon and humic acid; microbial biomass carbon with labile carbon, hot water extractable organic carbon, humic acid and fulvic acid; phosphomonoesterase activity with hot water extractable carbon, humic acid, fulvic acid and microbial biomass carbon; dehydrogenase activity with hot water extractable organic carbon, humic acid, fulvic acid and microbial biomass carbon; mean weight diameter with hot water extractable organic carbon, humic acid and fulvic acid.Less labile carbon and non labile carbon showed negative correlation with almost all the parameters. Aggregation was higher in macroaggregates than microaggregates and in upper layers of soil mainly 0-20 cm and 20-40 cm soil layers. Growing of napier grass and also setaria, seemed to have greater influence on soil aggregation as compared to other crops. Different forms of aggregate associated soil organic carbons were higher in fodder crops than virgin soils and aggregate associated total organic carbon, oxidisable organic carbon (%), hot water extractable organic carbon, cold water extractable organic carbon, humic acid and fulvic acid, very labile carbon and labile carbon of soils were higher in 0.25 mm to 1.00 mm size range of aggregates in case of both fodder crops and virgin soils. Very labile carbon and labile carbon content were higher in 0.5 mm to 0.10 mm size range than 0.25 mm size range. The aggregates in the size range of 0.50 and 0.25 mm contained higher humic acid as compared to the other size ranges.The aggregate associated less labile carbon per cent were higher in case of macroaggregates. The non labile carbon was higher in 20-40 cm soil depth and in 5.00 mm, 2.00 mm and 0.10 mm size range of aggregates than 0.25 mm to 1.00 mm size range. It is seen that continuous cultivation of napier showed highest percentage of aggregate associated different forms of soil carbon.ThesisItem Open Access Characterization and Fertility Capability Classification of soils under different landforms of Dhemaji district, Assam(2023) Saikia, Tikendrajit; Dutta, MaramiThe present investigation was undertaken in Dhemaji district of Assam in order to study the physical and chemical properties of soils and to evaluate the fertility capability classification of soils under different landforms. Three different landforms viz., piedmont plain (P1 & P2), alluvial plain (P3, P4, P5 & P6), flood plain (P7 & P8) were selected and horizon wise profile samples were collected from these three landforms. The study area experienced a mean annual rainfall of 3009.19 mm and mean annual temperature of 23.16°C. The soil temperature and moisture regime were hyperthermic and udic, respectively. The colour of the studied soil samples in all three landforms ranges from grey to brownish yellow with a dominant hue of 10 YR except in C1 horizon of P1 under piedmont plain where the hue was 7.5 YR. The value ranged from 3 to 6 and chroma 1 to 6. A textural variation ranging from sandy loam to loam in surface horizons and loamy sand to clay loam in sub surface was observed. Sand, silt and clay contents in these soils varied from 32.35 to 85.00, 9.00 to 50.60 and 4.40 to 34.02 per cent, respectively. Higher clay content was recorded in alluvial plain soils (34.02 per cent). Organic carbon content in the soil varied from 0.06 to 0.98 per cent, showing decreasing trend with depth with some exceptions in alluvial plain and flood plain soils. Soil pH varied from 4.81 to 6.44. Higher pH was recorded for flood plain soils on profile weighted mean basis. The cation exchange capacity (CEC) varied from 2.01 to 14.26 cmol (p+) kg-1 soil. On the basis of profile weighted mean, highest CEC value was recorded in piedmont plain soils. Among the basic cations, Ca2+ was the dominant cation. Per cent base saturation ranged from 18.07 to 62.52. The CBD extractable Al (Ald) and Fe (Fed) varied from 0.45 to 1.30 and 0.33 to 0.86 per cent, respectively. Soils were classified as Aquic Udorthents (P1, P7 and P8), Typic Udorthents (P5), Aquic Udifluvents (P6), Typic Dystrudepts (P2 and P3) and Typic Endoaquepts (P4). The amount of available N, P2O5 and K2O ranged from 12.54 (low) to 238.34 (low) kg ha-1, 2.56 (low) to 74.38 (high) kg ha-1 and 21.45 (low) to 193.24 (medium) kg ha-1, respectively. In general these nutrients tended to decrease with depth with few exceptions. DTPA- extractable Fe, Mn, Cu status was found to be high in all the soils and Zn was low to high. Hot water soluble B status was found to be low to high in all the soils. The soils of P1 (piedmont plain), P6 (alluvial plain), P7 and P8 (flood plain) were found to be loamy (L) in type and sandy (S) in sub strata type. Rest of the pedons viz., P2 (piedmont plain), P3, P4 and P5 (alluvial plain) were loamy (L) in both type and sub strata type. Finally after considering all the modifiers the fertility capability units were designated as ‘LSakm(1-3)’, ‘LLakm(1-3)’, ‘LLaek(0-1)’, ‘LLak(0-1)’, ‘LLhk(0-1)’, ‘LSak(0-1)’, ‘LShkm(0-1)’and ‘LSakm(0-1)’ for P1, P2, P3, P4, P5,P6, P7 and P8, respectively.ThesisItem Open Access Influence of organo-mineral fertilizer on soil acidity, phosphorus availability and potato yield after winter rice(2023) Borah, Rini; Borah, NilayA field experiment was conducted in ICR farm, AAU, Jorhat during November 2022 to February 2023 to assess the acidity and phosphorus availability in soil and yield of potato (Variety- Kufri Lalima) as influenced by organo-mineral fertilizer after winter rice. The experiment was conducted in a randomized block design (RBD) comprising individual plot size of 3 m X 3 m with three replications and seven treatments. The treatments included unfertilized plot, recommended doses (RD) of N:P2O5:K2O fertilizer @ 60:100:100 kg ha-1 (RDF) with farmyard manure (FYM) @ 5 t ha-1, RDF with FYM @ 2 t ha-1, RDF with vermicompost prepared substituting 30% of FYM by poultry litter (PLV) @ 2 t ha-1, RDN and 40% RD- PK with PLV @ 2 t ha-1, RDN and 60% RD- PK with PLV @ 2 t ha-1, RDN and 80% RD- PK with PLV @ 2 t ha-1. The PLV treatments were applied in two equal splits at planting and at 30 DAP as instant mixture with mineral fertilizers. The exchange acidity of soil was not influenced by nutrient management practices at 15, 30 and 45 days after planting of potato (DAP). RDF with PLV 2 t ha-1 significantly lowered the soil exchange acidity at 60 and 75 DAP over the unfertilized plot. The exchangeable H+ decreased at 45 and 60 DAP but exchangeable Al3+ was not affected by the treatments. The soil pH increased due to application of organo-mineral fertilizer at 15 and 45 DAP and decreased at 30, 60 and 75 DAP. The available phosphorus of fertilized soil was higher than initial value throughout the growth stages of potato. Application of RDF with FYM 5 t ha-1 or with PLV 2 t ha-1 significantly increased available P in soil at 15 and 30 DAP over RDF with FYM 2 t ha-1 and RDN + 40% RD-PK + PLV 2 t ha-1 instant mixture. The available phosphorus in soil increased at 30 DAP and decreased thereafter up to 75 DAP. The water extractable phosphorus showed similar trend as to available P at 15 and 30 DAP among the treatments. The water extractable P was relatively higher at 15 DAP and 45 DAP compared to other sampling dates, irrespective of the treatments. The available N and K content of soil increased with application of RDF with FYM 5 t ha-1 or with PLV 2 t ha-1 at stolon formation and tuber development stages. The plant growth, quality, yield attributing characters and yield of potato increased significantly with application of RDF with FYM 5 t ha-1 or with PLV 2 t ha-1. The nutrient content of tuber and haulm was not affected by the treatments. The total nutrient uptake by potato increased with application of organo- mineral fertilizer over the unfertilized plot. The soil pH, organic carbon, available P and K contents in soil after harvest of potato were significantly higher with fertilizer application compared to the unfertilized plot. The highest net benefit in terms of B:C ratio was observed with application of RDF with FYM 5 t ha-1 (1.72).ThesisItem Open Access EFFECT OF LIME AND ZINC ON STRAWBERRY YIELD AND QUALITY IN RICE-FALLOW SOIL(2023) Teronpi, Malin; Barooah, AradhanaA field experiment was carried out to study the “Effect of lime and zinc on strawberry yield and quality in rice fallow soil” at ICR Farm, Jorhat, during 2022-23. The aim of the experiment was to evaluate the effect of lime and zinc and its application method on yield and quality of strawberry in rice fallow soil. The experiment was done with 2 treatments in the main plot consisting of lime @ 500 kg ha-1 and unlimed, in the sub plots 5 treatments were applied as: T1- Control, T2- N:P:K @ 10:7:7 g / sq. m, T3- RDF + Zn @1.0 kg/ha, T4- RDF + Zn @2.0 kg/ha and T5- RDF + Zn 0.1% foliar spray at 30, 45, 60 and 75 DAP following split plot design with four replications. Application of lime showed significant increase in soil pH, available phosphorous, exchangeable Ca2+ and Mg2+ content. Changes in soil pH, available K, exchangeable Ca2+ and Mg2+ was found to be non-significant among the nutrient treatments, but phosphorous content was highly significant in application of RDF at 30 DAP and then gradually decreased with increase in number of days. Liming did not significantly affect Available N, available K and DTPA Zn content of soil. Among nutrient management practices, significantly higher available N and DTPA Zn was found in application of RDF + Zn @2.0 kg/ha. Available K was nonsignificant among the treatments. Application of lime significantly decreased all the forms of soil acidity and changes in different forms of soil acidity were non-significant among the treatments in the sub-plot. Plant growth parameters like plant height was non significantly influenced by application of lime but application of RDF + Zn 0.1% foliar spray showed the highest plant height at 75 DAP. Liming significantly increased the number of leaves from 45 DAP and application of RDF + Zn 0.1% foliar spray showed the maximum number of leaves at 75 DAP. Application of lime and nutrient management did not influence the leaf relative water content. The days to first flowering and the number of flowers per plant was highly influenced by application of lime. Application of RDF + Zn 0.1% foliar spray showed the minimum number of days required for first flowering and maximum number of flowers per plant. Plant yield parameters like number of fruits per plant, fruit weight and yield and B:C ratio was greatly influenced by application of lime. Among nutrient management, maximum number of fruits per plant, fruit weight, yield and B:C ratio was observed in application of RDF + Zn 0.1% foliar spray. Application of lime and RDF + Zn 0.1% foliar spray significantly enhanced total Zn content of strawberry fruit. After harvesting of strawberry, the soil pH and available P were found to be highly significant by liming whereas available nitrogen and DTPA Zn of soil was found highest in the application of RDF + Zn @ 2 kg/ha as basal and available P was highest in the application of RDF. Strawberry quality parameters like TSS, titratable acidity, ascorbic acid, reducing sugar, non-reducing sugar and total sugar was highly significant in the main plot. Maximum TSS, minimum titratable acidity, maximum ascorbic acid, Reducing sugar, Nonreducing sugar and Total sugar was observed in the application of RDF + Zn 0.1% foliar spray. A sensory evaluation was also conducted and found that flavour, sweetness and appearance of fruit were significantly increased by application of lime. Among nutrient treatments, application of RDF + Zn 0.1% foliar spray reported the significantly higher value in skin colour, pulp colour, flavour, sweetness and appearance.ThesisItem Open Access Phosphate dynamics in Maize (Zea mays) as influenced by zeolite enabled nano phosphatic fertilizer(2023) Das, Dipika; Kandali, Gayatri GoswamiA pot culture experiment was carried out to study the “Phosphate dynamics in Maize (Zea mays) as influenced by zeolite enabled nano phosphatic fertilizer” during 2022-23. The aim of the experiment was to study the phosphate dynamics in maize and the release pattern of phosphorus for a period of 75 days at 15 days interval taking five treatments including treatments with Zeolite based nano-P fertilizers which was already synthesized and characterized. The treatments with nano fertilizers were 100% RDP through nano P fertilizer and reduced doses of 60% and 80% RDP through nano P fertilizer. These treatments were compared with an absolute control and a treatment where recommended dose of P was applied through chemical fertilizer taking the recommended dose of maize as the rate of phosphorus application. Three different types of soil collected from various locations of Jorhat, Titabar and Majuli representing different textural classes viz. silty clay loam, clay loam and sandy clay loam were taken for the study. Treatment receiving 100% RDP through nanofertilizer showed minimum concentration of available P from 0 days upto 15 days and thereafter it gradually increased reaching its maximum value in 60 days of interval period. Similar trend were observed for other treatments receiving nano P with reduced doses. Such trend was same for the two soils with textures sandy clay loam and silty clay loam whereas clay loam soil showed a gradual increase in available P throughout the cropping period reaching its peak at 75 days and thereafter declined. Highest concentration of P at 60 days interval was found in treatment receiving 100% RDP through nanofertilizer which was statistically higher than treatment receiving RDP through SSP. Significant difference in P release was found between 100% nano P and treatment receiving 60% of RDP through nano fertilizer in all the three type of soil. No significant difference in P release was found between treatments receiving 60% and 80% RDP through nano P. Significant difference in phosphorus content and uptake in grain and straw was found between absolute control, RDP through SSP and RDP through nano P fertilizer. However no significance difference was found between the treatments receiving 100% RDP through nano and the reduced doses of 60 % and 80% RDP through nano P. This trend followed in all the three types of soil. Correlation coefficients among soil available phosphorus concentration at 15 days with corresponding plant phosphorus concentration at 15 days was found to be non significant. However the same was found to be highly significant during the other days of interval.The first order kinetic constant was found to increase from T2 to T5 which might be due to less fixation of P by soil components. In case of second order kinetics, the decrease in rate constant value means increase in the release of P, which is dependent upon both soil solution and soil matrix. The parabolic diffusion equation was best fit for describing the P release as compared to the other two kinetic models.ThesisItem Open Access Phosphorus Adsorption and Desorption Characteristics in Acid Soil under Intensive Cropping Systems(2023) Dutta, Boishali; Das, Kulendra NathThe present study was carried out during 2022-2023 to investigate phosphorus adsorption and desorption characteristics in acid soil under intensive cropping systems in the on-going experimental trial on “Identification of cropping systems module for different farming systems” since 2018-2019 under All India Coordinated Research Project on Integrated Farming Systems at Instructional-cum-Research farm AAU, Jorhat. The experiment was laid out in randomized block design consisting of three replications of ten different treatments viz., T1: Winter Rice- Autumn Rice, T2: Winter rice-Toria, T3: Winter rice-Pea-Cowpea, T4: Green manure-Toria-Black gram, T5: Winter rice-Rajmah-Cowpea, T6: Winter rice-Toria-Black gram, T7: Teosinte-Oat-Cowpea, T8: Maize-Oat-Rice bean, T9: Ridge gourd-Broccoli-Lady’s finger, T10: Bitter gourd-Tomato-French bean. Phosphate adsorption and desorption studies were conducted on surface soil samples (0-15 cm) and the adsorption data were fitted into Langmuir and Freundlich equations. The soils were acidic in reaction (pH 5.15 -5.37) with significant variations in soil organic carbon, available NPK, free Fe and Al oxides, CEC and exchangeable Ca2+ and Mg2+. The inorganic P fractions of soils under cropping systems followed the trend of Fe-P>Al-P>Ca-P>Sa-P. All these fractions were positively correlated with total-P (624.43-766.23 mg kg-1) indicating dynamic equilibrium amongst them. The organic P ranged from 94.92-135.92 mg kg-1 and was positively correlated with soil organic carbon. Phosphorus adsorption study revealed an increase in the absolute amount of adsorbed P (x/m) and decrease in per cent of added P adsorbed (Xad) and distribution coefficient (Kd) with increasing P levels (Co) in all the studied soils. Phosphorus adsorption was highest in T2 consisting of winter rice-toria cropping system (18.0-1240.5 μg P ml-1) and was lowest in T4 containing green manure-toria-black gram (16.7- 609.8 μg P ml-1). Freundlich adsorption isotherm showed a better fit of adsorption data with higher levels of significance (R2≥ 0.98) than Langmuir adsorption isotherms. The Langmuir adsorption maxima (b) and Freundlich K showed highest values in treatment T2 and the lowest values in treatment T4. Similar but reverse trend was observed in desorption study in the above treatments with special reference to treatment T4 where P desorption was highest. The desorption data were well fitted to Freundlich equation (R2=0.99). It was observed that, only small portion of adsorbed P was desorbed suggesting partial reversibly in P adsorption. The respective values of phosphate adsorption and desorption were highest and lowest in nearby virgin soil than all the cropping systems. Changes in soil properties under the influence of different management aspects in cropping sequences were responsible for such observations. The Phosphorus Supply Parameter (SP) at various initial concentrations gradually increased with increasing exogenous P. Strong positive and negative correlation of SP at a given level of added P with soil pH and free iron and aluminium oxides, respectively, implied their influences on P availability. Thus, the present study revealed that, inclusion of green manure and legume crops in the cropping sequence lowered P adsorption and increased P desorption resulting in higher P supply to crops and hence intensive (triple) cropping tended to eliminate negative impacts on P adsorption in soil systems under long term cultivation.ThesisItem Open Access Study on Soil Health and Carbon Fractions under Intensive Cropping Systems(2023) Bora, Bhaswati; Gogoi, BhabeshThe research reports on the effect of intensive cropping systems on soil properties in the acid Inceptisol of north-east India are not adequately available. Therefore, a study was carried out during 2021-22 at Instructional-cum-Research Farm, Assam Agricultural University (AAU), Jorhat to investigate the impact of different cropping sequences on the physico-chemical and biological properties of soil. The present study forms a part of the experimental trial on “Identification of cropping systems module for different farming systems” that has been going on since 2018-19 under the All India Coordinated Research Project on Integrated Farming Systems at AAU, Jorhat. The experiment was laid out in a Randomized Block Design replicating 3 times with 10 treatment combinations viz.,T1: Winter rice-Autumn rice, T2: Winter rice-Toria, T3: Winter rice-Pea-Cowpea, T4: Green manure- Toria-Blackgram, T5: Winter rice-Rajmah-Cowpea, T6: Winter rice-Toria-Blackgram, T7: Teosinte-Oat-Cowpea, T8: Maize-Oat-Rice bean, T9: Ridge gourd-Broccoli-Lady’s finger and T10:Bittergourd-Tomato-French bean sequence. Results revealed that the effect of intensive cropping system on soil bulk density and water holding capacity were nonsignificant. However, aggregate size and infiltration rate were significantly affected by the various cropping sequences. The highest mean weight diameter and infiltration rate were recorded under T10 and T4 respectively. Significant variations were also observed in soil pH, cation exchange capacity (CEC) and electrical conductivity (EC) after the end of the cropping sequences. The highest soil pH and CEC were recorded in T4, whereas EC was found to be the highest in case of T3. Significantly highest organic carbon content in soil was recorded in T4 followed by T9. Ammoniacal and nitrate N content in soil varied from 28.33 to 38.30 and 15.90 to 22.53 kg ha-1, respectively. Significant variations in available N, P2O5 and K2O status in soil were recorded at the end of the cropping sequences due to long-term cultivation of various cropping sequences. The highest soil available N and P2O5 were recorded in T4, whereas the lowest was in T1. Available K in soil was found to be the highest in T9 followed by T4 . Exchangeable calcium and magnesium content in soil ranged from 0.91 to 1.20 and 0.47 to 0.65 c mol (p+) kg-1, respectively. The available sulphur ranged from 11.70 to 17.13 kg ha-1 and the highest was recorded in T9 (Ridge gourd-Broccoli-Lady’s finger) followed by T4. DTPA micronutrients (Fe, Mn, Zn and Cu) in soil were significantly affected by the various cropping sequences and treatment T4 and T5 recorded highest values. Data on dehydrogenase, phosphomonesterase and urease activities varied from 95.5 to 141.1μg TTF g-1soil 24 h-1, 117.3 to 145.5 μg p-nitrophenol g-1 soil h-1 and 1.50 to 2.70 μg NH4-N g-1 soil h-1, respectively. Microbial biomass C, water soluble C, very labile and labile C fractions v were recorded highest in T4 with Green manure-Toria-Black gram sequence. The treatment under Ridge gourd-Broccoli-Ladys finger sequence (T9) showed the highest content of less labile and non-labile C fractions in soil. The total organic C and total C content in soil were found to be the highest in T4, whereas the highest total inorganic C was recorded in case of T5. Data on soil organic C stock under intensive cropping systems varied significantly from the lowest 45.27 Mg ha-1 under T7 to the highest 56.84 Mg ha-1 under T4. The effect of various cropping sequences on NPK uptake by the cropping sequences showed significant variations, and the data on rice equivalent yield was also varied significantly from the lowest 24.89 to the highest 656.45 q ha-1. The highest benefit: cost ratios (4.33 and 3.70) were recorded in case of the cropping sequences meant for income enhancement i.e. in T9 and T10, respectively. Correlation studies showed positive correlations of physico- chemical properties (except bulk density) with available nutrient status and C fractions in soil. Overall, the present study revealed that the inclusion of green manure and legume crops in the cropping sequences sustains soil productivity and hence triple cropping is possible without having negative impact in the soil system under long-term.
