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Open Access
Effects of Conservation Tillage and Herbicide Application on Soil Microbial Activity in Rice-Mustard Sequence
(AAU, Jorhat, 2019-07) Parit, Rajat Kumar; Mahanta, Kaberi
The study on the “Effect of Conservation Tillage and Herbicide Application on Soil Microbial Activity in Rice-Mustard sequence”in the year 2018-2019 which forms a part of the long term trial under AICRP on Weed Management that was established during 2016 at Instructional-cum-Research (ICR) farm of Assam Agricultural University. The experiment was laid out in randomized block design replicating three times with five treatments in winter rice and mustard crop separately. The treatments of winter rice was comprised of treatments viz., T1- CT (Conventional tillage)+ Transplanting, T2- CT+Transplanting+ Pretilachlor, T3- CT+ Direct Seeded +Pretilachlor, T4- MT (Minimum tillage)+ Direct Seeded +Pretilachlor and T5- MT+ Direct Seeded+ Residue +Pretilachlor. Similarly, the treatments of mustard crop was comprised of treatments viz., T1-CT, T2- MT+ Pendimethalin, T3- CT+ Pendimethalin, T4- MT+ Residues+ Pendimethalin, T5- MT+ Residues+ Pendimethalin.The physical and chemical properties viz., bulk density, porosity, water holding capacity, pH, CEC and available nutrients viz; nitrogen, phosphorus, potassium, calcium, magnesium and soil organic carbon were determined from surface soil samples collected after the harvest of both winter rice and mustard crop. Conservation tillage i.e. MT along with residue has improved soil physical properties like bulk density, porosity, water holding capacity and CEC except the pH of the soil did not vary significantly. The soil organic carbon content increased significantly due to MT, herbicide application and residues. Available nitrogen, phosphorus, potassium, calcium and magnesium content of the soil was recorded in the medium range with highest available nitrogen, phosphorus, potassium, calcium and magnesium content recorded in the treatment T5 receiving MT+ Residues+ Herbicide Application in both winter rice and mustard crop. Biological parameters were analysed from surface soils collected periodically at 0, 3, 7, 15, 30, 45, 60 DAA of the herbicide in both winter rice and mustard crop. After the study, MT was found to improve the major enzymatic activities, soil microbial biomass carbon, physicochemical properties, available nutrients and soil organic carbon content as compared to conventional tillage (CT). Application of pretilachlor in winter rice showed a decline in β-glucosidase and urease activity for first 15 DAA and then increased till harvesting. However, a stimulatory effect was observed on activity of acid phosphatase, dehydrogenase and microbial biomass carbon for short period of time which later on decreased. Application of pendimethalin in mustard caused a decrease in dehydrogenase and β-glucosidase in initial stage while it increased the activity of acid phosphatse, urease and microbial biomass carbon in initial stage. Regarding the effect of herbicide application on available nutrients and soil organic carbon content it showed a stimulatory effect on these parameters. Significantly higher enzyme activities were recorded in treatments T5 which was comprised of MT+ Residues+ Herbicide Application.
Open Access
Ecological Occurrences of Methylotrophs in Phyllosphere of crops
(AAU, Jorhat, 2019-07) Phukan, Sanghamitra; Gayan, Anjuma
The phyllosphere is an ecologically important habitat that hosts a large and diverse microbial community. Bacteria are among the most abundant inhabitants of the phyllospheric leaf surface, where the conditions are very harsh, due to heat, irradiation, rainfall, etc. The present investigation envisages the isolation, biochemical characterization and screening of phyllosphericmethlyotrophic bacteria associated with various crops for their plant growth promoting characteristics. Methylotrophs are a group of microorganisms that have the ability to utilize C1 compounds such as methanol or formaldehyde along with several multi carbon compounds, the most common genera being Methylobacterium, comprising mostly of pink pigmented facultative methylotroph (PPFM). In the present investigation leaf samples were collected from different crops comprising of five sites of Jorhat district, Assam. Leaf being the dominant aerial part, was considered for isolation purpose. Following the leaf imprinting and serial dilution technique, isolation of phyllopshericmethylotrophic bacteria were carried out. Eighteen isolates were screened for their plant growth promoting traits like Indole acetic acid (IAA), siderophore production, antibiotic resistance, ammonia production, etc. All the isolates produced IAA within a range of 0.69- 5.53 μg g⁻¹, with the highest in spinach (M16). The total nitrogen content of the isolates ranged between 1.4- 2.6 mg g⁻¹. Siderophore production was shown by the isolates M1 (chili) and M10 (cauliflower) and resistance to common antibiotics was also shown by few isolates, isolate M4,M15, M16 and M 17 from ivy gourd, cowpea, spinach and french bean crops respectively. Isolates M1, M10 and M12, retrieved from the phyllopshere of chilli and cauliflower crop possessed the ability to solubilize phosphorus, and isolate M7 from phyllosphere of tomato could solubilize zinc. After screening for plant growth promoting traits, twelve isolates were finally selected for a series of biochemical tests. All the isolates could hydrolyze casein, but none could hydrolyze starch. Catalase test was positive for all the isolates but all isolates did not possess cytochrome c oxidase enzyme. Few isolates M1, M4, M7, M10, M15, M16, M17 from chilli, ivy gourd, tomato, cauliflower, cowpea, spinach and frenchbean showed nitrate reduction. The isolate M13 showed positive urease activity. Citrate utilization was seen only in case of one isolate from phyllosphere of french bean (M17). Few isolates could show positive results for indole and VogesProskauer’s test but methyl red test was positive for one isolate from phyllosphere of chillicrop. Enumeration of methylotrophic bacterial population carried out for both phyllosphere samples and rhizospheric soil, resulted in a higher population in the phyllosphere. Soil samples of the study site were also analyzed for soil chemical (pH, available N, available P2O5,available K2O, organic carbon) and biological parameters (microbial biomass carbon, fluorescein diactetate, phosphomonoesterase). Correlation studies between the population of methylotroph in leaf and that of rhizospheric soil resulted in positive correlation (r=0.762*). Phyllospheric population of the methylotrophic bacteria and soil pH of the study sites also resulted in a positive correlation(r=0.934**). From the research initiative, it could be inferred that a wide array of methylotrophic bacteria occur in the phyllosphere of different crops, and possess plant growth promoting traits. These phyllosphericmethylotrophic bacteria could further be utilized for coinoculation with biofertilizers or used as bioinoculantsin crop improvement.
Open Access
EFFECT OF NUTRIENT MANAGEMENT ON PHOSPHORUS TRANSFORMATION AND ITS INFLUENCE ON YIELD OF BELL PEPPER (Capsicum annum) UNDER PROTECTED CULTIVATION
(AAU, Jorhat, 2019-07) Dutta, Arindam Kumar; Tamuly, Danish
The present investigation entitled "Effect of Nutrient Management on Phosphorus transformation and its influence on yield of Bell pepper (Capsicum annum) under protected cultivation was carried out in the Horticulture Farm of AAU, Jorhat- 13. The experiment was conducted maintaining Split-split design having three(3) factors(Nitrogen, Phosphorus and Potassium) and each having three (3) levels(N- 80,100,120 P-40,60,80 K-40,60,80) accounting for a total treatment combination of twenty seven (27) having replicated thrice(3). Small portion of soils was collected from different treatments under protected cultivation at a depth of 0-15 cm. The soil samples were collected at two different stages of the crop viz., flowering and fruiting stages i.e 45 and 115 DAP respectively and was analyzed for different physico-chemical properties. The initial study revealed that the texture was silty loam with a bulk density of 1.176g cm-3 and the particle density 1.18 Mg m-3. Organic C (%) was found in the high range (0.94%) with a CEC of 13.7 cmol(p+) kg-1 of soil. The soil was acidic with a pH value of 5.32. Soil was having initial NPK content i.e 535.66 kg ha-1, 36.25 kg ha-1 and 68.56 kg ha-1 respectively. The present study revealed that the single factor effect of treatment has a significant effect on soil chemical properties, plant nutrient partitioning and various forms of P, except for Residual P which was found to be non-significant. The interaction effect of NP found to be significant with the physico-chemical parameters .The NP interaction with plant nutrient partitioning found that the highest values (3.383%,1.365%N and 0.385,0.366%P) of leaf and shoot nitrogen and phosphorus content are obtained in the higher dose of nutrients(N120P80) and highest value in leaf and shoot K(4.996% and 4.126%) are found in low to medium dose of fertilizer in the flowering stage but in the fruiting stage, higher values are obtained in the medium dose of NP levels . NP interaction with different forms of P is also found to be significant and the highest values are obtained in medium to high dose of fertilizer (N-100,120 and P-60,80). Available P and exchangeable Ca and Mg were found to be high in the low level of NK interaction. The leaf and shoot N and K content tends to increase with the increase level of NK fertilizers. Various forms of P were found to be high in the low to medium level of NK interaction (N-80,100 and K-40,60). For PK interaction, Available N was found to be highest (766.5 kg ha-1) in the low to medium dose of PK and available P2O5 & K2O were found to be high in higher level of treatments (P80K80). CEC was found to be non-significant in the flowering stage but found to be significant in the Fruiting stage. Similar results were found as in NK interaction with the plant nutrient partitioning i.e high NPK leaf and shoot content were found in the medium to high level of PK. Different forms of P were also found to be significant with the PK interaction and the highest values were observed with the higher dose of P. In the Interaction effect of NPK, all the physico-chemical properties are found to be significant. The plant nutrient partitioning and the various forms of P, except for Residual P were also found to be significant with the interaction effect of NPK. The present study suggested that the nutrient management was found to influence the physico-chemical properties of the soil as well as various forms of P, except for Residual-P. The different forms of P were found to poorly explain the yield variability and did not influence yield directly. This implies that time may be a limiting factor for conversion of applied phosphorus to different P fractions. Different soil P fractions may influence the yield indirectly through other soil factors as founded by use of appropriate statistical tools. Furthermore, only N was found to be playing a dominant role in predicting the yield of capsicum under protected cultivation. The time of application of N also plays a vital role for the increased production of capsicum. The application of N just before fruiting stage gave better result compared to other critical growth stages during the study period. The best treatment combinations for higher yield of capsicum were when medium to high dose of N (N-100, 120) and P (P-60, 80) and low to medium dose of K (K-40, 60) was applied. Further studies may be conducted at different physio-geographical locations to get a robust nutrient recommendation for capsicum under protected cultivation.
Open Access
PHOSPHATE ADSORPTION IN SOILS OF ASSAM IN RELATION TO PHYSICO-CHEMICAL PROPERTIES AND PLANT UPTAKE
(AAU, Jorhat, 2019-07) RAJKHOWA, MONTRISHNA; Bhattacharyya, D.
The study investigated the Phosphate (P) adsorption in four (4) major soil orders of Assam. It was conducted in sixteen (16) surface (0-30 cm) and sub-surface (30-60 cm) soil samples, collected from two locations each of the order Entisol, Inceptisol, Alfisol and Ultisol. There were wide variations in physico-chemical characteristics of the soils with pH, organic carbon, texture, clay content, CEC, AEC, per cent base saturation (PBS) and free oxides of Fe and Al which ranged from 4.86 to 5.60, 0.66 to 1.17 per cent, sandy loam to clay , 18 to 39.5 per cent , 6.72 to 19.73 cmol (P+) kg–1, 1.64 to 2.80 cmol (-) kg-1, 21.16 to 44.39 per cent, 1.08 to 3.21 per cent and 0.60 to 1.08 per cent, respectively. In the soils forms of phosphorus present in variable amounts but had the same sequence of abundance viz., Fe-P>Al-P>Organic P>Residual-P>Ca-P in all soils. Total acidity of the soils ranged from 1.60 to 3.36 cmol (p+) kg-1. Forms of acidity revealed that total potential acidity was the most dominant forms acidity followed by pH dependent acidity, exchangeable acidity and total acidity in soils of Assam. The adsorption of P in the soils was studied by conducting batch experiment in the laboratory by equilibrating two (2) g soil in duplicate with 20 ml 0.01 M CaCl2 solution containing 5, 10, 20, 40, 60, 80, 100 and 150 mg P L-1 as KH2PO4. The results of adsorption studies on P were discussed in terms of per cent adsorption of added P (%AdsP), Langmuir and Freundlich adsorption parameters. The per cent of adsorbed P (%AdsP) decreased with the increased of added P. The P adsorption data was found to be the best fit in Langmuir adsorption isotherm when resolved into two parts.The Langmuir parameters viz., the adsorption maxima (b) were higher for part II (upper part) whereas the bonding energy constant (k) was higher for part I (lower part) of the isotherms. The highest b2 of part II was found in Ultisol (5882.35 mg kg-1 in S8d1) and the lowest was found in Entisol (1037mg/kg in S1d2).The highest bonding energy constant (k) value for part I was observed in Ultisol (0.795 L mg-1) and the lowest in Entisol (0.055 L mg-1). Phosphate adsorption maxima (b1) of part I had a significant positive correlation with OC (r = 0.814**), clay content (r = 0.632**), Ex. Ca (r=0.701**), CEC (r = 0.874**) and free Fe2O3(r = 0.840**), toal P (r = 0.541*), Fe-P (r = 0.607*) and Al-P (r = 0.512*) content of the soils. The bonding energy constant (k1) of the part I and part II of the isotherm was found to have significant positive correlations with OC (r = 0.731** and 716** ), clay (r = 0.655** and 0.642**), CEC (r=0.890** and 0.640**) and Fe2O3 (r = 0.732** and 815**) of the soils, respectively. Freundlich adsorption parameter K had a significant positive correlation with OC (r = 0.801**), CEC(r=0.908**), clay content (r = 0.660**), Ex. Ca(r=0.537*), Free Fe2O3(r = 0.810**) and Al2O3 (r = 0.571*) of the soils. The Bray 1 P significantly negatively correlated with P adsorption maxima (b1) (r = - 0.599*), bonding energy constant (k1) (r = - 0.594*), MPBC (r = - 0.599*) and Freundlich’s n (r = - 0.744*) and K (r = - 0.616*). Bray2 P also significantly negatively correlated with P adsorption maxima(r= - 0.668**), MPBC (r = - 0.533*) and Freundlich’s n (r = - 0.736**) and K (r= -.571**). P uptake was highest in soil S5d1 (0.042 g plant-1) and lowest in soil S4d1 (0.027 and 0.026 g plant-1) with as well as without addition of P. The P uptake by the Maize had no significant correlation with P adsorption parameters. It might be due to greater role of the intensity factor viz. P concentration and diffusion in supply of P to plant root than the P adsorption parameters. Therefore, amount of P required to obtain 0.2 mg P L-1 in equilibrium soil solution was different in different soil orders. It was highest in Ultisol S8d1 (90.89 mg PL-1) and the lowest in Entisol S2d1 (32.78 mg PL-1). The values of P supply parameter (SP) ranged from 0.38 in soil S7d1 to 49.38 in soil S3d2. Thus the findings of present investigation on P adsorption capacity of soils of Assam will be useful in P fertilizer management and recommendation of P fertilizer for growing crops in these soils.
Open Access
TARGETED YIELD BASED FERTILIZER PRESCRIPTION MODEL FOR SCENTED RICE
(AAU, Jorhat, 2019-07) DOLEY, MOMIN; Das, K. N.
Field experiments were conducted at the Instructional-cum-Research (ICR) Farm, Assam Agricultural University, Jorhat during the year 2017-18 and 2018-19 to generate Targeted Yield based Fertilizer Prescription Model for Scented Rice. In order to develop fertilizer prescription equations, fertility gradient experiment was conducted taking kharif rice (cv. Ranjit) as exhaust crop by creating three fertility gradient strips. After harvest of gradient crop, test crop experiment was conducted in the same field with scented rice (cv. Keteki joha) by superimposing 24 treatment combinations consisting of five levels of N (0, 10, 20, 40 and 60 kg ha-1), four levels of P2O5 (0, 5, 10 and 20 kg ha-1), three levels of K2O (0, 10 and 20 kg ha-1) and three levels of vermicompost (0, 2 and 3 t ha-1) in each of these fertility gradient strips. Integrated nutrient management approach brought about a positive influence on organic carbon, soil available nutrient status, crop yield and uptake of nutrients by scented rice. Combined application of 60 kg N, 10 kg P2O5 and 10 kg K2O per hectare along with 3 tonnes of vermicompost per hectare resulted the highest available NPK in soil along with the highest crop yield and uptake of nitrogen, phosphorus and potassium by rice as compared to other treatments. Fertilizer prescription equations were formulated for scented rice by following Ramamoorthy’s Inductive- cum-targeted yield approach. Based on the experiments, the nutrient requirement (NR) for producing one quintal of scented rice was found to be 2.96, 0.21and 2.67 kg q-1 with respect to N, P and K, respectively. The soil efficiency for N, P and K was found to be 36.44%, 37.13%, 50.17% in 2017-18, respectively and 35.33%, 32.88%, 49.87% in 2018-19, respectively and 35.89, 35.01, 50.02 kg q-1 in pooled analysis, respectively. The N, P, K contributions to scented rice from fertilizers were 52.22%, 23.08%, 63.55%, respectively in 2017-18 and 54.43%, 23.04%, 64.13%, respectively in 2018-19 and 53.33, 23.06, 63.84 kg q-1, respectively in pooled analysis and found highest in K-fertilizer. Conversely, the per cent contribution of N, P and K from organic component that is organic efficiency was 9.69%, 1.08%, 21.6%, respectively in 2017-18 and 10.57%, 1.15%, 22.4%, respectively in 2018-19 and 10.13, 1.12, 22 kg q-1, respectively in pooled and found to be unassuming in all the nutrients. Based on nutrient requirement, contribution from soil, contribution from fertilizer and contribution from organic manure the fertilizer prescription equations were developed for scented rice (cv. Keteki joha) and an estimate of fertilizer doses were formulated in the form of ready reckoner for a range of soil test values and desired yield targets.
Open Access
VARIABILITY OF GROUND WATER RECHARGE CHARACTERISTICS AND QUALITY IN JORHAT DISTRICT, ASSAM
(AAU, Jorhat, 2019-07) Saikia, Mridupawan; Patgiri, D. K.
The present investigation was carried out in Jorhat District aimed at assessment of the groundwater, its recharge characteristics and quality. The district spread from 93o58’32” to 94o36’24”E longitude and 26o20’51” to 26o56’29” N latitude. Soil and water samples were collected from 265 randomly selected GPS enabled locations of Jorhat district at an interval of around 4-5 km. Representative soil and water samples were collected from each location (both disturbed and core sample) from two depths viz. 0-30 and 30-60 cm. Depth of groundwater in each location were recorded during the months of January, April, July and October in 2017 and 2018 as well. Thematic maps were prepared using the GIS software TNTMips. Geostatistical parameters were computed following standard methods. The bulk density and particle density ranged from 1.16-1.59 and 2.24-2.65 mg/m3 in 0-30 cm depth and 1.19-1.61 and 2.28-2.68 mg/m3 in 30-60 cm depth. The bulk density of the soil showed negative significant correlation with porosity and water content at 0.1 to 15 bar matric suction in both the depths.The Organic carbon content 0-30 cm depth ranged from 0.87-1.86 per cent while at 30-60 cm depth it ranged from 0.38-1.21 per cent. The soil pH in both the depths were acidic and ranged from 4.50-6.60 and 4.23-6.84 at 0-30 and 30-60 cm depth, respectively.The texture of the soils ranged from heavy towards the higher elevation to light towards the lower elevation areas.The Porosity and Saturation water content ranged from 33.47-53.28 and 19.87-43.19 per cent in 0-30 cm depth and 34.76-53.28 and 19.73-42.34 per cent in 30-60 cm depth respectively. Porosity showed significant positive correlation with organic carbon and clay and negative significant correlation with sand. With increase in matric suction of the soil from 0.1 bar to 15 bar the water content of the soil decreased.The pore interaction (b) parameter ranged from 2.03-3.56 in 0-30 cm depth and 1.94-3.96 in 30-60 cm depth. The mean saturated hydraulic conductivity of the soils for the two depths were 1.01 and 0.65, respectively, indicating higher saturated hydraulic conductivity at surface as compared to sub-surface soil. Saturated hydraulic conductivity showed positive correlation with sand and negative correlation with clay. Ground water table depth during January and April were very low, while it reached surface during July and October for both 2017 and 2018. Groundwater depth during all the months during 2017 showed mixed correlation with physico-chemical properties.Thematic maps revealed the pattern of groundwater movement in different range.The decline during first quarter in both the years indicated wide ranging variability.Thus, it is quite obvious that the soil properties associated with transport of water both in saturated and unsaturated condition favoured transport of water.The groundwater table during the quarter July to October, 2017 and 2018 indicated that in some of the areas, the same did not decline at all and were at surface. The rate of decline of groundwater table becomes faster with the arrival of the dry season for which during the quarter from October, 2017 to January, 2018 groundwater table declined from 64.00 to 139.00cm. During the quarter from January to April, 2018 decline in groundwater table indicated that although there were general decline, the same was less than that of the corresponding quarter in the previous year. This maybe due to the fact that the region received some amount of rainfall during the quarter and the entire quantity may have helped reduce the rate of decline of groundwater in 2018.The region received pre-monsoon shower during the months of April and May and the groundwater table during the quarter from April to July, 2018 rose from 82.00 to 220.00 cm. This rise is considerable considering the fact that the average rise was 170.30 cm indicating that whatever the rainfall is received, the same had invariably gone down the profile and recharged it. Thus, it made up for the decline of groundwater table during the previous months. The pH, zinc, calcium, magnesium, fluoride, aluminium and boron content of groundwater of the district are all within permissible limit set by WHO. However, iron and arsenic content in groundwater are far beyond permissible limit set by WHOand need some treatment to make it potable. The semivariogram parameters for depth of groundwater in Jorhat District during the period of study reveals that the trend of nugget and sill variance followed the trend of fluctuation of depth of groundwater table during the period of study. The nugget/sill ratio revealed that in almost all the months the variability was medium to high. Data on semivariogram parameters for the different quality parameters for groundwater revealed that Arsenic and Chloride showed the lowest and highest nugget and sill, respectively. The ratio of MAE, MRE and RMSE between kriging and IDW revealed that the ratios were more than 1, indicating that kriging estimated these parameters higher than that of Inverse distance weighting (IDW). Thus, this indicated that IDW was a better method of interpolation for these parameters. IDW method of interpolation improvised the maps from 0.93 to 12.25 per cent.
Open Access
NITROGEN DYNAMICS IN A RICE-RICE SYSTEM OF UPPER BRAHMAPUTRA VALLEY ZONE (UBVZ) OF ASSAM
(AAU, Jorhat, 2019-05) Tamuli, Babita; Bhattacharyya, Devajit
The study investigated mineral N and labile soil organic N dynamics at different growth stages of rice and their distribution within soil depth (0-80 cm) under various combinations of inorganic and organic fertilization in a rice-rice cropping system of UBVZ of Assam. Further partial balance of mineral N and total N stock of the soils were determined. The study was conducted in a long term fertility experiment at Regional Agricultural Research Station (RARS), Assam Agricultural University, Titabar, Jorhat in 2017 taking the selected treatments viz., Control, 100% NPK, 100% NPK + FYM 5t/ha, 50% NPK, 50% NPK+ 50% (FYM) N and FYM 10t/ha for rabi and kharif rice cropping sequence. Soil samples were collected from different depth (0-20, 20-40, 40-60 and 60-80 cm) before transplanting of rabi rice, at active tillering, flowering and physiological maturity stages of rabi and kharif rice and after harvest of kharif rice. Physiochemical properties analysed in the soils collected before transplanting of rabi rice of 2017 was considered as initial. Soil samples of three growth stages of rabi and kharif rice were analysed for mineral and labile soil organic N. Straw and grain samples collected at harvest of rabi and kharif rice were analysed for their N concentration and N uptake. Partial balance of soil mineral N in surface soils (0-20 cm) and total N stock within 0-80 cm soil depth was estimated at the end of the cropping sequence. The pH of the soils was higher in treatments FYM 10t/ha (5.87), 100% NPK+ FYM 5t/ha (5.72) and 50% NPK+ 50% (FYM) N (5.67) than the control (5.33) but was significantly lower in treatments 100% NPK (5.13) and 50% NPK (5.25). Soil organic carbon (OC) content had built up significantly in all the treatments compared to control. Organic carbon decreased significantly with increased soil depth. The bulk density (BD) of the soils varied from 1.18 (FYM 10t/ha) to 1.36 g cm−3 (control). The highest total and mineral N before transplanting of rabi rice and after harvest of kharif rice was recorded in 100% NPK+ FYM 5t/ha which was significantly higher over rest of the treatments. In the study of mineral N dynamics, NO3-N and NH4-N were found to be significantly higher in 100% NPK+FYM 5t/ha fertilized plots at the three growth stages in both rabi and kharif rice. The higher NO3-N at active tillering stage was 12.73 and 11.53 mg kg-1 in rabi and kharif rice, respectively, in 100% NPK+FYM 5t/ha fertilization, which gradually decreased at physiological maturity stages of both the rice season (10.70 mg kg-1 in rabi and 9.94 mg kg-1 in kharif). Similar decreasing trend was also observed in NH4-N from active tillering (10.67-17.59 mg kg-1 in rabi and 8.67-16.67 mg kg-1 in kharif) to physiological maturity stages (9.22-16.53 mg kg-1 in rabi and 6.76-14.39 mg kg-1 in kharif). Both NH4-N and NO3 -N showed a distinct decreasing trend with increase in soil depth. The significantly the highest grain (4.66 and 5.54 t ha−1 ) and straw (6.58 and 6.64 t ha−1 ) yield of rabi and kharif rice and total N uptake were observed in 100% NPK+ FYM 5t/ha treated plots. However, this grain yield was statistically at par with yield in treatments 100% NPK at rabi and FYM 10t/ha and 100% NPK in kharif rice. The soil partial mineral N balance revealed that with application of inorganic fertilizer (100% NPK and 50% NPK) and with no fertilizer application (control) resulted in a negative partial soil N balance. However, application different combinations of organic FYM and inorganic NPK fertilizers as well as 10t/ha FYM alone had lead to positive N balance in soils as well as higher N stock. The highest N balance (18.74 kg ha-1) and N stock (1.51 Mg ha-1) was found in application of 100% NPK + FYM 5t/ha followed by that in application of FYM 10t/ha (3.63 kg ha-1 and 1.33 Mg ha-1, respectively). The labile soil organic N fractions of the soils viz., microbial biomass N (MBN), particulate organic N (PON) and water extractable organic N (WEON) was decreasing with increase in crop growth from active tillering to physiological maturity stage. The decrease in MBN, PON and WEON in rabi varied from 10.85-16.85 to 9.65-16.03 mg kg-1, 0.21-0.89 to 0.14-0.68 g kg−1 and 6.64-12.43 to 5.31-10.68 mg kg-1, respectively; and in kharif from 8.45-13.04 to 7.28-12.0 mg kg-1, 0.16-0.57 to 0.1-0.48 g kg−1, 4.87-9.49 to 3.48-7.95 mg kg-1, respectively.The labile soil organic N fractions were significantly higher in FYM 10t/ha treated plots which might be due to creation of suitable conditions for microbial growth by FYM. All the labile fractions of soil organic N decreased significantly with increase in soil depth. This might be due to decrease of OC with soil depth. The N fractions of the soils viz., NO3-N, NH4-N, MBN, PON and WEON showed a significant positive correlation with soil OC and total N content at the three growth stages in rabi and kharif season. Multiple regression analysis of grain yield with various fractions of N showed that NH4-N (R2=0.745) was the main contributor to the grain yield at early growth stage of rabi rice. Whereas, WEON (R2=0.901) was the main contributor to the grain yield in kharif rice. The results of the investigation indicated that the NH4-N and NO3-N were the main contributor to the total uptake of N at three different growth stages in both the rice season. All the fractions of N were significantly and positively correlated with each other (p<0.01). Most of the N mineralized in the soil was expected to occur in the labile N fractions. The positive correlation observed between labile N fractions and mineral N also supported their close interrelation. The multiple regression analysis of various N fractions with total N stock indicated that NH4-N was the main contributor to the N stock of the studied soils under rice-rice cropping system. The present investigation leads to the conclusion that combined applications of 5 t/ha FYM with 100% NPK at present could be considered as the best nutrient management practices in rice-rice system of UBVZ of Assam in terms of the highest yield, N balance, N stock and sustainable soil health (pH, OC and BD). Moreover, the treatment of organic nutrient management 10t FYM/ha could also produce rice yield statistically at par with 100% NPK + FYM 5t/ha, had positive N balance and was the best treatment for sustainable soil health. Therefore, better organic nutrient management which could produce higher yield than 10t FYM/ha might be the present requirement for the rice-rice system of the UBVZ of Assam.
Open Access
ASSESSMENT OF CARBON FOOTPRINT IN RICE-RICE CROPPING SYSTEM AS AFFECTED BY FERTILIZER MANAGEMENT
(AAU, Jorhat, 2019-07) Borah, Rupjyoti; D, K.N.
The present study aimed at assessing the carbon footprint in rice-rice cropping system as affected by various fertilizer management combinations and source of nitrogen was carried out in the ICR Farm, AAU (26°71'N, 94°18' E) 91.0 m above MSL during the years 2016-17 and 2017-18. The initial pH, organic carbon, available N, P2O5 and K2O of the experimental plot were 5.84, 0.61%, 132.561 kg ha-1, 214.48 kg ha-1 and 33.734 kg ha-1, respectively. There were no significant differences in soil pH amongst the variety while significant differences were observed within various fertilizer combinations and source of N. Soil organic carbon values ranged between 0.62 to 0.85% and significant difference was observed amongst the fertilizer treatments and source of N. The various fertilizer combinations in case of available nitrogen also showed a similar trend with the highest mean value of 169.84 kg Nha-1 in the treatment with full recommended dose of fertilizer (RDF). Available P2O5 in the system also followed a similar trend (36.07 kg ha-1) while available K2O significantly varied within the varieties and fertilizer combinations with higher values in Mahsuri-Banglami system (49.94 kg K2O ha-1). Significant differences in methane emissions were observed amongst the varieties and also in between the fertilizer combination treatments.The methane emission was 388.33 mg m-2hr-1 in Ranjit-Lachit system and 285.61 mgm-2hr-1 in the Mahsuri-Banglami cropping system. High methane emission was observed in RDF followed by 50% RDF+Vermicompost and INM. During the entire crop growing season, the largest variation in methane emission was observed in the early growth period. Methane emission indicated two distinct peaks during the entire crop growth period, irrespective of the treatments. Peaks of nitrous oxide emissions were obtained after topdressing of nitrogenous fertilizers. Significant variations were also observed in between the fertilizer combination treatments may be due to varying organic carbon in the various treatments. Ranjit-Lachit system recorded higher mean cumulative N2O emissions (10.72 gm-2) than Mahsuri-Banglami system (4.92 gm-2). The RDF treatments recorded highest mean cumulative N2O emissions amongst the fertilizer combinations. Temporal pattern of flux irrespective of treatments showed a trend of gradual increase with the growth of the crop, thereafter a slow decline in fluxes. The highest mean cumulative CO2 emissions (2953.43 mg m-2) was recorded in the Ranjit-Lachit system and within the fertilizer combinations, the highest mean value of 3125.20 mg m-2 was recorded under RDF treatment. Mapping of the three different tiers of carbon footprint showed that the tier-1 was the dominant contributor of carbon footprint. The Total System Spatial Carbon Footprint (SCF) under different treatments recorded higher values in case of INM treatments involving 50%NP + Full K + 5t/ha enriched compost and vermicompost treatments in both the cropping systems. Within the INM treatments, higher SCF of 62.00 t CE ha-1 was obtained in Ranjit-Lachit system while in case of Mahsuri-Banglami system, the highest SCF was obtained in INM treatment with NCU and UCU (48.91 t CE ha-1). Yield scaled carbon footprint (YCF) indicated highest value of 13.23 kg CE kg-1 grain in case of Mahsuri-Banglami system while 50% RDF supplemented with 5 t ha-1vermicompost and uncoated urea recorded the highest YCF with 15.96 kg CE kg-1 of grain in Ranjit-Lachit cropping system. Considering the yield compensation and sustainability of the soil resources, the INM with slow release N source proved to be the better in rice-rice cropping system.
Open Access
CHANGES IN SOIL BIOLOGICAL PARAMETERS AS EFFECTED BY THE APPLICATION OF ORGANIC INPUTS IN RICE-TORIA SEQUENCE
(AAU, Jorhat, 2019-07) Chauhan, Manoj Kumar; Baruah, Rajen
The field trials were conducted to assess the changes in soil chemical and biological parameters along with yield and yield attributing characters of rice and toria crops in sequence during 2015-17. The treatment combinations were as Control (T1), 50% recommended dose of fertilizer (RDF)+50% biofertilzer (BF) (T2), 50% RDF+50% Enriched Compost (EC) (T3), 100% RDF (T4), 100% BF (T5) and 100% EC (T6). The data were recorded at various stages of crop growth and soil samples were analysed for different characters at different stages of rice and toria crops. The results showed that the treatment T3 consisting of 50% EC and 50% RDF recorded the highest accumulation of N (265.49 and 258.01 kg/ha), P (23.14 and 23.00 kg/ha), and K (152.94 and 148.38 kg/ha) at maximum tillering stage of rice and flowering stage of toria, respectively but remained at par with 100% RDF treatment in both the crops during the period of investigations. The accumulation of organic carbon (12.49 g/kg soil in rice and 12.14 g/kg soil in toria) was recorded significantly higher than 100% RDF treatment (11.01 g/kg soil in rice and 10.60 g/kg soil in toria) at similar stages of both the crops which remained at par with 100% EC (T6) treatment. Soil accumulation of Organic carbon (OC), N, P and K was found higher in T6 treatment over T5 treatment. However, soil accumulation of OC, N, P and K gradually declined from maximum tillering stages of rice and flowering stage of toria to harvesting stage of both the crops. Although no significant changes in soil pH was recorded, but the lowest pH was recorded in T4 treatment in both the crops ranging from pH 5.19 to pH 5.22, even lower than the initial soil pH value of 5.24. The results revealed that the bacterial, fungal and actinomycetes population varied with the treatments and with the stage of the crops. The treatments comprising of 50% EC and 50% RDF (T3) recorded the highest bacterial population of 19.63 cfu x105/g and 19.25 cfu x105/g soil at flowering stages of rice and toria, respectively. The fungal population was 9.12 cfu x105/g soil in rice and 8.88 cfu x105/g soil in toria, respectively. The actinomycetes population was 45.75 cfu x104/g soil in rice and 45.12 cfu x104/g soil in toria at flowering stages of rice and toria crops and declined thereafter at harvesting stages of both the crops. The microbial diversity in T3 and other organic treatments found significantly higher than 100% RDF and control treatment. Soil respiration, microbial biomass carbon, and soil enzymes (fluorescein di-acetate activity, dehydrogenase activity, acid phosphatase activity and urease activity) behaved differently with different treatment whereas T3 (50% EC + 50% RDF) exhibited the best performance over other treatments at all the stages of rice and toria crops during both the years. All the biological parameters were found at their peak at flowering stages and declined thereafter at harvesting stages of both the crops. All the bio-chemical properties in treated plots in rice-toria sequence were found significantly higher than the untreated control and even over the initial values of each parameters. Unlike soil bio-chemical properties, agronomic parameters of rice (no. of tillers/hill, plant height, panicle length, grain and straw yield) and toria (plant height, no. of siliqua/plant, grain and stover yield) crops recorded higher values in 100% RDF (T4) treatment which remained at par with, 50% EC + 50% RDF treatment (T3). The grain yield of rice (45.09 q/ha) and toria (893.38 kg/ha) in the 100% fertilized plots (T4) were found at par with T3 treatment (43.72 q/ha in rice 885.63 kg/ha in toria) receiving 50% EC and 50% RDF, but both recorded significantly higher yield over sole application of biofertilizer, enriched compost and control treatment. The beneficial effect of INM treatment (T3) that facilitated favourable soil conditions were reflected in grain yield of both rice and toria crops which was equivalent even with 100% RDF treatments. Rice yield was more closely and positively correlated (at p<0.05) with OC (r=0.587*), N (r=0.932*), P (r=0.746*) and K (r=0.972*) as compared to soil enzymes such as acid phosphatase (r=0.637*), urease (r=0.512*). Similarly, a strong relationship was also recorded among toria yield with OC, N, P and K and other soil biochemical properties. Furthermore, soil respiration and MBC exhibited strong relationship both in rice (r=0.961*) and toria (r=0.966*) crop. All the soil biological properties registered positive correlation with chemical properties of soil.

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