Soils Of Punjab Research Articles

Distribution of Forms of Copper and their Association with Soil Properties and Uptake in Major Soil Orders in Semi-arid Soils of Punjab, India

Profiles of semi-arid-zone soils in Punjab, northwestern India, were investigated for different forms of copper (Cu), including total Cu, diethylenetriaminepentaacetic acid (DTPA)–extractable Cu, soil solution plus exchangeable Cu, Cu adsorbed onto inorganic sites, Cu bound by organic sites, and Cu adsorbed onto oxide surfaces. When all soils were considered, total Cu content ranged from 7 to 37 mg kg−1, while DTPA-extractable and soil solution plus exchangeable Cu contents ranged from 0.30 to 3.26 mg kg−1 and from 0.02 to 0.43 mg kg−1, respectively. Copper adsorbed onto inorganic sites ranged from 0.62 to 2.6 mg kg−1 and that onto oxide surfaces ranged from 2.0 to 13.2 mg kg−1. The Cu bound by organic sites ranged from 1.2 to 12.2 mg kg−1. The magnitudes of different forms of Cu in soils did not exhibit any consistent pattern of distribution. Organic matter and size fractions (clay and silt) had a strong influence on the distribution of different forms of Cu. The content of all forms of Cu was generally greater in the fine-textured Alfisols and Inceptisols than coarse-textured Entisols. Soil solution plus exchangeable Cu, Cu held onto organic sites, and and Cu adsorbed onto inorganic sites (crystalline) had significant positive correlations with organic carbon and silt contents.The DTPA Cu was positively correlated with organic carbon, silt, and clay contents. Total Cu content strongly correlated with silt and clay contents of soils. Among the forms, Cu held on the organic site, water soluble + exchangeable Cu, and Cu adsorbed onto oxide surface were positively correlated with DTPA-extractable Cu. The DTPA-extractable Cu and soil solution plus exchangeable Cu seems to be good indices of Cu availability in soils and can be used for correction of Cu deficiency in the soils of the region. The uptake of Cu was greater in fine-textured Inceptisols and Alfisols than coarse-textured Entisols. Among the different forms only DTPA-extractable Cu was positively correlated with total uptake of Cu.

Forms of Boron and its Distribution in Saline-Alkali Soils

Seven forms of boron (B) using different extractants were determined in salt affected benchmark soils of Punjab. The soil pH varied from 8.60 to 10.24, EC from 0.13 to 4.8 dS m−1, CaCO3 content from 0.30 to 26.8 g kg−1 and organic C from 1.1 to 5.5 g kg−1. The content of water soluble (WS-B), hot water soluble (HWS-B), hot 0.01 M CaCl2 soluble (HCC-B), acid soluble (HCl-B), leachable or mannitol extractable (Mann-B) and AB-DTPA extractable B in salt affected soils of Punjab, ranged from 0.16 to 2.48, 0.30 to 4.80, 0.20 to 3.20, 0.32 to 3.40, 0.28 to 4.20 and 0.14 to 0.84 mg kg−1 soil, respectively. Forms of B were positively and significantly related with soil pH and EC. Total B ranged from 11.26 to 30.25 mg kg−1 and was non-significantly correlated with other forms. The HWS-B was significantly correlated with HCC-B (r = 0.969**). Regression equation showed 97 to 99% variations in WS-B, HWS-B, HCC-B, HCl-B, Mann-B, and AB-DTPA-B while only 77% in total B content governed by various soil properties.

Effect of long-term use of inorganic and integrated fertilization on soil phosphorus fractions in rice-wheat cropping system

Soil phosphorus (P) fractions as affected by long-term use of inorganic and integrated fertilization under rice-wheat cropping system in loamy sand soil of Punjab, India were studied. The inorganic P fractions improved with increase in rate of P applied. The Ca-P is the dominating P fractions in these soils. The inorganic P fraction improved with fertilizer and the effect was pronounced under integrated fertilizer application. The pH and EC were negatively and significantly correlated with Sa-P, Al-P, Fe-P and Ca-P, however, the soil OC significantly and positively correlated with these fractions. The Sa-P and Al-P were major sources of Olsen’s exchangeable soil P and were in equilibrium with Fe-P and Ca-P. The crop production (grain and straw yield) significantly improved with fertilizer. Grain yield and total P uptake by rice was positively and significantly correlated with all soil inorganic P fractions.

Changes in some Physico-Chemical characteristics of soils under poplar based agroforestry

Physical and chemical properties of soil in poplar (Populus deltoides Bartr.) plantations were evaluated in the alluvial soils of Punjab. The results showed that there was an overall improvement in the soil physical and chemical characteristics under poplar plantations. The magnitude of effects improved with increase in the number of cutting cycles of poplar. A decrease in soil pH and an increase in electrical conductivity (EC) were observed under higher age plantations. In the surface soil layer, the pH values ranged from 8.25 to 8.45 under different treatments. No significant effect of cutting cycles of poplar was observed on soil bulk density and particle density. Significant improvement in water holding capacity and cation exchange capacity with increase in cutting cycles of poplar plantations was observed upto 30 cm of depth. A general reduction in soil physical and chemical parameters with increase in soil depth was observed under different cutting cycles. The soil pH was lower whereas EC, bulk density, water holding capacity and cation exchange capacity were higher under paddy-wheat sequence than the poplar plantations.

Microscale distribution and elemental associations of Se in seleniferous soils in Punjab, India.

Several regions around the globe are known to have soils highly enriched in Se. Usually, bulk samples are analysed when characterizing enrichment and mobility of Se in seleniferous soils. In this study, Se concentration and distribution were determined along with other elements on a microscale level in seleniferous soils from Punjab, India, using synchrotron-based X-ray fluorescence (XRF) analysis. Additionally, the mineralogical and geochemical composition of bulk soil material was investigated. Sequential extractions were carried out to gain further insight into preferential Se associations. The objective of this study was to investigate the microscale geochemistry of seleniferous soils in order to be able to deduce information about Se host phases, to characterize the distribution, extent and origin of Se enrichment and to possibly reveal the relevant enrichment processes. Selenium concentrations in the soils vary considerably within tens of micrometers. Thirty times the bulk concentration, the highest Se enrichment was found to be 350mg/kg. Results show that the primary origin of Se in these soils is probably not from weathering of bedrock or alluvium but rather from an external Se source, like Se-rich irrigation water. Secondary processes like in situ formation of mineral phases, adsorption or transformation to organic species finally lead to an immobilization and fixation of Se in the soils. In this context, reduction of Se oxyanions to elemental Se or to selenide as part of sulfides probably leads to the highest Se enrichment which, however, is mainly spatially confined. Lower Se enrichments are indicated to be due to (co-)precipitation with or adsorption to calcite. Therefore, this extremely heterogeneous distribution of Se must be controlled by small-scale differences in redox and solution chemistry which can develop in small soil structure like micropores or soil aggregates.

Forms of Boron in Alkaline Alluvial Soils in Relation to Soil Properties and Their Contribution to Available and Total Boron Pool

In alkaline alluvial soils of Punjab, located in northern India, seven forms of boron (B) were compared using different extractants. The comparison was assessed in relation to soil properties and their contribution to soil available and total B pool. The mean contents of water-soluble (WS-B), hot-water-soluble (HWS-B), hot 0.01 M calcium chloride (CaCl2)–soluble (HCC-B), acid-soluble (HCl-B), leachable or mannitol-extractable (Mann-B), ammonium bicarbonate diethylenetriaminepentaacetic acid (AB-DTPA)–extractable, and total B in alluvium-derived soils of Punjab were 0.24, 0.49, 0.50, 0.53, 0.55, 0.19, and 17.04 mg kg−1 soil, respectively. All the forms of B were related with soil properties, especially organic carbon (C) content, clay content, texture, and cation exchange capacity. Different forms were correlated significantly with each other. Total B content ranged from 10.25 to 25.42 mg kg−1 and was nonsignificantly correlated with other forms of B. All the forms of B were positively and significantly correlated with organic C content, clay content, and cation exchange capacity while negatively correlated with soil pH, electrical conductivity, and sand content. The most commonly used form of B, i.e., hot water-soluble B, was significantly correlated with hot 0.01 M CaCl2–extractable B (r = 0.885**). Regression equations showed that 85, 94, 95, 88, 90, and 86% variations in WS-B, HWS-B, HCC-B, HCl-B, Mann-B, and AB DTPA-B contents were governed by various soil properties.

Simulation of the evaporation of soil water beneath a wheat crop canopy

The evaporation of soil water (Es) is an important component of the water balance in cropping systems. Although Es is considered to be non-beneficial (not directly related to crop production), it may indirectly influence water availability for transpiration which is directly related to crop growth and thus yield. Due to the difficulty in measuring Es, empirical models are usually used, especially Ritchie's two stage model. Ritchie's model assumes that stage 1 evaporation is dependent on radiant energy at the soil surface, and that during stage 2, Es is independent of radiant energy. During stage 2, the model assumes that Es is only dependent on soil hydraulic properties, and that cumulative stage 2 Es is proportional to the square root of time. To evaluate the model, we measured Es under the canopy of wheat grown on a clay loam soil in Punjab, India, using mini-lysimeters. Soil evaporation during three different potential evaporation (Eo) periods (1.5, 3.0, 6.0mmd−1) was compared during the 2006–2007 and 2007–2008 wheat seasons. The results suggested that stage 2 Es was affected by Eo, and cumulative Es was not described well by a square root of time function. An exponential decay function which describes the decrease in Es/Eo as a function of a soil dependent constant (b), whose value is directly related to Eo, was developed. Using this function, calculated cumulative Es for two independent drying periods was close to the observed Es values with coefficients of determination of 0.82 and 0.95.

Screening of wheat cultivars and fertifortification with zinc, manganese and iron in low fertility soils of Punjab

The present investigation was carried out for two consecutive years (2008–09 and 2009–10) at research farm of Department of Soil Science, Punjab Agricultural University, Ludhiana on a loamy sand soil (Typic Ustochrept) to enrich wheat grains with Zn, Mn and Fe through foliar application. Six wheat cultivars viz. V1-PBW 343, V2-PBW 550, V3-PBW 17, V4-PDW 233, V5-PDW 274 and V6-PDW 291 were selected including durum and aestivum cultivars. Four foliar sprays @ 0.5 per cent each of Zn, Mn and Fe were applied starting from maximum tillering, flower initiation milk and dough stages. It was revealed that foliar application of Zn, Mn and Fe increased the grain yield in wheat. The aestivum cultivars reported higher grain yield compared to durum cultivars. This study indicates that 17.3–38.8% enrichment with Zn and 13.1–30.3% with Fe is possible through foliar application Foliar application of 0.5% each of Zn and Fe separately at different stages of wheat growth significantly increased the grain yield of wheat. All the wheat varieties showed significant increase in Zn and Fe concentrations over control.

Antagonistic and plant growth promoting activities of endophytic and soil actinomycetes

The objective of this study was the isolation and screening of actinomycete isolates for antagonistic potential and plant growth promoting activities. A total of 321 isolates were recovered from different plants, their rhizospheric soils and non-rhizospheric soils of Punjab and Himachal Pradesh regions. Out of these, 62 were endophytic, 156 were rhizospheric and 103 were non-rhizospheric isolates. In primary screening (dual culture assay), 83 isolates antagonised one or more test phytopathogenic fungi. From these active isolates, 20 were found to be antagonistic in well diffusion assay (secondary screening) and most of them demonstrated broad spectrum inhibitory activity against five to six test fungi. Studies on plant growth promoting activities revealed that 12 showed abilities to produce indole acetic acid, 10 produced siderophores and 12 showed ammonia production. Phosphate solubilisation was observed in five isolates and four fixed atmospheric N2. In addition, production of hydrolytic enzymes such as chitinase, amylase, cellulase and protease was demonstrated by five, twenty, eleven and eleven isolates, respectively. The results of this study indicate that these isolates may be used as biocontrol and plant growth promoting agents. Morphological and chemotaxonomic studies revealed that all the active isolates belonged to the genus Streptomyces

Effects of Organic Matter and Ionic Strength of Supporting Electrolyte on Zinc Adsorption in Benchmark Soils of Punjab in Northwest India

Organic matter is one of the most important components of soil and influences the physical and chemical properties of the soil. Its presence increases the adsorption of zinc (Zn). Zinc adsorption by soils and soil components is highly influenced by ionic composition, species, and concentration of supporting electrolyte solution. The present investigation was carried out to study adsorption behavior of Zn in the presence of supporting electrolytes and aqueous media for eight benchmark soils of Punjab, varying in physical and chemical characteristics. The effect of ionic strength on the adsorption of Zn was studied in the presence and absence of organic matter using three different concentrations (viz., 0.001, 0.01, and 0.1 M) of sodium sulfate (Na2SO4) as an electrolyte. The results revealed that Zn adsorption was greater in the presence of organic matter (untreated soils) than in the absence of organic matter (treated soils). The adsorption decreased after the removal of organic matter both in the presence of 0.01 M Na2SO4 and in aqueous medium. Zinc adsorption data conformed to Langmuir and Freundlich adsorption equations for both organic matter and ionic strength factors. The Langmuir constants, Freundlich constants, and distribution coefficient Kd were determined. Partial molar free energy change () decreased after the removal of organic matter both in the presence of 0.01 M Na2SO4 and in aqueous medium.

Induction of Sporulation By Different Nitrogen Sources InAnabaena naviculoides, A Diazotrophic Strain Capable of Colonizing Paddy Field Soil of Punjab (India)

Anabaena naviculoides is a filamentous cyanobacterium that is capable of heterotrophy and cellular differentiation into nitrogen-fixing heterocysts and desiccating thick walled spores, the akinetes. In the present study, the role of different nitrogen sources on akinete differentiation has been studied in the rice field cyanobacterium Anabaena naviculoides. All the vegetative cells transformrd into thick walled akinetes. In Chu-10 basal culture medium, the initiation of akinete differentiation was noticeable on 8th day and all the vegetative cells differentiated into akinetes by 50th day. Whereas among different nitrogen sources (ammonium sulphate, potassium nitrate, sodium nitrite, ammonium nitrate, Urea, ammonium chloride) employed, only potassium nitrate and sodium nitrite (2-10mM) enhanced the cyanobacterial growth and akinete development of the test organism. These two nitrogen sources shortened (32-36d) the period of akinete differentiation than the control cultures (50 d) and supported 100% (at 10mM) in a span of 32–36 days of culture. These akinetes (in dry state) remained viable for 105–150 days while vegetative cells under similar storage conditions (at 40°C) lost their viability after 15 days.

Arsenic mobilization in alluvial soils of Punjab, North–West India under flood irrigation practices

A laboratory investigation was carried out to examine the mechanism of arsenic (As) mobilization under flooded conditions (24 and 240 h) in 18 alluvial soils of Punjab, North–West India. Total dissolved As increased from a range of 3–16 μg L−1 (mean 9 μg L−1) to a range of 33–1,761 μg L−1 (mean 392 μg L−1) with the increase in flooding period from 24 to 240 h. The amount of As mobilization varied depending upon redox potential (pe) created by flooding conditions. After 24 h of flooded conditions, pe of soil water suspension ranged from −1.75 to 0.77 (mean −0.24). Increasing the flooding period to 240 h, pe of soil water suspension decreased in the range of −4.49 to −2.74 (mean −3.29). Pourbaix diagram identified arsenate (HAsO4 2−) as predominant species in most of the alluvial soil–water suspensions under oxidized conditions, after 24 h of equilibration period, which ultimately transformed to arsenite (H3AsO3 0) after 240 h of anaerobic condition due to more reduced status. The solid phase identified was orpiment (As2S3). Identification of iron and manganese species in alluvial soil water suspension by Pourbaix diagram indicated decline in both soluble Fe2+ and SO4 2− concentration due to the formation of iron sulfide mineral phase after 240 h under anaerobic conditions. In these soils, decline in soluble Fe was also due to the precipitation of vivianite [Fe3(PO4)2·8H2O]. Elevated arsenic content and low pe value were measured in aquifers located in paddy growing fields comparative to aquifers of other sites. Large degree of variability in As concentrations was recorded in aquifers located at same sites. Thus, it is better to analyze each aquifer for their As content rather than to depends on the prediction on As content of neighbouring wells. The present investigation elucidates that flood irrigation practices in Punjab for growing paddy crop could induce the geochemical conditions favorable to mobilize arsenic from surface soils which could eventually elevate its content in the underlying shallow aquifers. Water abstracted from these aquifers by hand pumps or tube wells for drinking purposes could create hazards for local population due to loading with arsenic concentration above the safe limits. Thus, to avoid further contamination of shallow aquifers with arsenic, it is advisable to shift the flooded rice cultivation to other upland crops having lesser water requirement.

Formation of Se (0) Nanoparticles by Duganella sp. and Agrobacterium sp. isolated from Se-laden soil of North-East Punjab, India

BackgroundSelenium (Se) is an essential trace element, but is toxic at high concentrations. Depending upon the geological background, the land use or on anthropogenic pollution, different amounts of Se may be present in soil. Its toxicity is related to the oxyanions selenate and selenite as they are water soluble and bioavailable. Microorganisms play an important role in Se transformations in soil and its cycling in the environment by transforming water-soluble oxyanions into water insoluble, non-toxic elemental Se (0). For this study, soil samples were collected from selenium-contaminated agricultural soils of Punjab/India to enrich and isolate microbes that interacted with the Se cycle.ResultsA mixed microbial culture enriched from the arable soil of Punjab could reduce 230 mg/l of water soluble selenite to spherical Se (0) nanoparticles during aerobic growth as confirmed by SEM-EDX. Four pure cultures (C 1, C 4, C 6, C 7) of Gram negative, oxidase and catalase positive, aerobic bacteria were isolated from this mixed microbial consortium and identified by 16 S rDNA gene sequence alignment as two strains of Duganella sp. (C 1, C 4) and two strains of Agrobacterium sp.(C 6, C 7). SEM/TEM-EDX analyses of the culture broth of the four strains revealed excretion of uniformly round sharply contoured Se (0) nanoparticles by all cultures. Their size ranged from 140–200 nm in cultures of strains C 1 and C 4, and from 185–190 nm in cultures of strains C 6 and C 7. Both Duganella sp. revealed better selenite reduction efficiencies than the two Agrobacterium sp.ConclusionsThis is the first study reporting the capability of newly isolated, aerobically growing Duganella sp. and Agrobacterium sp. from soils of Punjab/India to form spherical, regularly formed Se (0) nanoparticles from water soluble selenite. Among others, the four strains may significantly contribute to the biogeochemical cycling of Se in soil. Bioconversion of toxic selenite to non-toxic Se (0) nanoparticles under aerobic conditions in general may be useful for detoxification of agricultural soil, since elemental Se may not be taken up by the roots of plants and thus allow non-dangerous fodder and food production on Se-containing soil.

Draft Genome Sequence of the Nitrophenol-Degrading Actinomycete Rhodococcus imtechensis RKJ300

We report the 8.231-Mb genome sequence of Rhodococcus imtechensis RKJ300, isolated from pesticide-contaminated soil in Punjab, India. The genome sequence of the strain RKJ300 will be helpful in exploring the molecular pathways involved in the degradation of nitrophenols.

Zinc Adsorption as Affected by Concentration, Temperature, and Time of Contact in the Presence of Electrolytic and Aqueous Medium in Benchmark Soils of Punjab in Northwest India

Adsorption of zinc (Zn) ions by soil colloids is significant because of its greater adsorbing surface, thus making it an important process in controlling Zn availability to plants. The adsorption processes depend upon a number of factors including temperature, pH, time of contact, clay content, and calcium carbonate content. Therefore, adsorption behavior of Zn was studied for eight benchmark soils of Punjab in northwestern India, varying widely in physical and chemical characteristics. The adsorption of Zn was studied at varying Zn concentrations, temperatures, and time of contact in the presence of 0.01 M sodium sulfate (Na2SO4) electrolyte and in aqueous medium. The greatest amount of Zn adsorbed in the presence of electrolyte and in aqueous medium (deionized water) was in arid series (Gahri Bhagi, Jassipauwali), followed by semi-arid series (Fatehpur, Kanjli) and subhumid series (Dhar, Chamror). The results revealed that irrespective of the soils, Zn adsorption increased with an increase in Zn concentration and decreased with an increase in temperature from 25 oC to 35 oC. Zinc adsorption was found to be greater in 0.01 M Na2SO4 solution as compared to aqueous medium. Further adsorption of Zn increased with increase in time of contact. The Zn adsorption data was well fitted to the Langmuir and Freundlich adsorption equations. The values of distribution coefficient Kd and partial molar free energy change () were greater in the presence of 0.01 M Na2SO4 as compared to aqueous medium, suggesting that greater driving force is involved in adsorption of Zn in the presence of 0.01 M Na2SO4 as compared to aqueous medium.

COMPARATIVE EFFICIENCY OF BORAX AND GRANUBOR AS BORON FERTILIZERS FOR LENTIL AND SOYBEAN GROWN ON ALLUVIAL ALKALINE SOILS

The two sources of boron (B), i.e., borax and granubor, were evaluated for their efficiency to lentil and soybean grown on alluvium derived soils of Punjab, India. Agronomic efficiency, physiological efficiency, and B recovery were estimated for both the sources and crops. The application of 0.75 kg B ha-1 through borax and granubor increased lentil seed yield by 21.4 and 23.3%, respectively, over control indicating 2% higher response with granubor application. Boron content in lentil seed increased from 12.2 μg g-1 in control treatment to the maximum of 24.1 μg g−1 with the application of 1.25 kg B ha−1 through granubor. There was 24.6% increase in seed yield of soybean with the application of 1.25 kg B ha−1 through either of fertilizer source. Total B content increased to maximum of 59.8% over control when B was applied through borax. Apparent B recovery% and recovery efficiency were higher for granubor compared to borax for both the crops.

Effect of organic amendments on uptake of selenium and biochemical grain composition of wheat and rape grown on seleniferous soils in northwestern India

AbstractCrops grown in seleniferous soil may accumulate selenium (Se) to levels considered highly toxic for animal and human consumption. Furthermore, higher Se content in plant tissues leads to considerable deterioration in product quality. Application of organic amendments plays an important role in improving soil physical, chemical, and biological conditions and influencing nutrient availability. A field trial was conducted to evaluate the effect of organic amendments, namely poultry manure (PM), sugar cane press mud (SCPM), and farmyard manure (FYM), on Se uptake and grain quality of wheat and oilseed rape grown on a seleniferous soil in Punjab, India. Selenium accumulation by wheat and oilseed rape grains decreased significantly (75%–95%) with the application of PM and SCPM, while FYM application resulted in a significant decrease (23%) only in case of wheat grains. The amount of Se associated with seed proteins varied in proportion to its uptake under different treatments. Quality of wheat grains improved considerably with respect to total soluble sugars, reducing sugars, starch, lipids, and sulfur concentrations only after application of SCPM and PM. Treating a Se‐contaminated soil with organic amendments significantly increased the oil concentration and changed the proportion of various fatty acids in rape grains. It is concluded that applying organic amendments to Se‐contaminated soils can alleviate the deleterious effects of Se and restore the nutritional quality of grains.

Distribution of different forms of Mn and their association with soil properties in arid zone soils of Punjab, India

Six pedons from arid zones soils of Punjab, north western India, were investigated for different forms of manganese (Mn): total Mn, diethylenetriamine penta-acetic acid (DTPA)-extractable Mn, soil solution plus exchangeable Mn, adsorbed Mn onto inorganic sites, and oxide surfaces, and Mn bound by organic sites. Total Mn content ranged from 241–517 mg kg−1, DTPA-extractable Mn content ranged from 1.40–4.52 mg kg−1, soil solution plus exchangeable Mn content ranged from 0.04–0.30 mg kg−1, Mn adsorbed onto inorganic sites ranged from 34–109 mg kg−1, and that onto oxide surfaces ranged from 28–173 mg kg−1. The Mn bound by organic sites ranged from 14–56 mg kg−1. The forms of Mn did not exhibit any consistent pattern of distribution. Irrespective of the different fractions of Mn their content was higher in the fine textured soils as compared to the coarse textured soils. The soil solution plus exchangeable Mn held onto organic site and oxide surface (amorphous) increased with increase in organic carbon, silt and clay contents. The Mn adsorbed onto inorganic site (crystalline) increased with only silt and clay content. The DTPA-Mn increased with increase in organic carbon content, whereas Mn adsorbed onto oxide surfaces increased with an increase in organic carbon, silt and clay. However, both these fractions decreased with an increase in calcium carbonate and pH. Total Mn was strongly correlated with organic carbon, silt and clay content of soil. Among the forms, Mn held on the organic site, water soluble + exchangeable and Mn adsorbed onto oxide surface were positively correlated with DTPA-extractable Mn. DTPA-extractable Mn and soil solution plus exchangeable Mn seem to be good indices of Mn availability in soils and are helpful for correction of Mn deficiency in the soils of the region.

Isolation and molecular characterisation of diazotrophic growth-promoting bacteria from wheat rhizospheric soils of Punjab

Diazotrophs are nitrogen-fixing bacteria which possess the nifH gene that codes for the nitrogenase enzyme involved in reduction of atmospheric dinitrogen to ammonia. Seventy-two diazotrophic bacteria were isolated using eight nitrogen-free media from wheat rhizospheric soil. The diazotrophic population was found to be negatively related to soil nitrogen, whereas a positive correlation was observed with organic carbon and electrical conductivity of soil. The isolates were initially identified on the basis of cultural, morphological, and biochemical characterisation. Various diazotrophic isolates were screened for functional activities. Thirty-seven isolates were acetylene reduction assay positive, among which 28 isolates exhibited nitrogenase activity ranging from 22.3 to 72.0 nmol C2H4/h. The majority of isolates were able to produce indole acetic acid ranging from 11.2 to 23.0 µg/mL and only a few diazotrophs could solubilise phosphate. These isolates showed amplification with two nifH primers (nifH1 and nifH2), thereby confirming their diazotrophic potential. The positive nifH isolates were further characterised using restriction fragment length polymorphism of 16S rDNA to reveal diversity among them. Based on UPGMA clustering and partial sequencing of 16S rDNA, the isolates were identified as Azotobacter sp., Azospirillum sp., Stenotrophomonas maltophilia, Stenotrophomonas sp., Sphingomonas paucimobilis, Rhizobium larrymoorei, Pseudomonas aeruginosa, and Xanthomonas oryzae.

Zinc Adsorption as Affected by Supporting Electrolyte in Benchmark Soils of Punjab in Northwest India

Surface zinc (Zn) adsorption is an important process that regulates the Zn concentration in the solution. The adsorption mechanism along with interacting cations and anions controls the concentration of Zn in the soil solution, which is immediately available to the plant roots. Therefore, the effect of supporting electrolytes on Zn adsorption was studied for eight benchmark soils of Punjab in northwest India. The investigation was undertaken in the presence of 0.01 M sodium sulfate (Na2SO4), 0.03 M sodium chloride (NaCl), 0.03 M sodium nitrate (NaNO3), and 0.01 M potassium sulfate (K2SO4) to study the effect of sulfate (SO4 2–), chloride (Cl–), nitrate (NO3 –), sodium (Na+), and potassium (K+). The greatest amount of Zn adsorbed in the presence of different anions was in the arid series (Gahri Bhagi, Jassipauwali) followed by the semi-arid series (Fatehpur, Kanjli) and subhumid series (Dhar, Chamror). The extent of adsorption in the presence of various anions in most of the soils followed the order as SO4 2– > Cl–> NO3 – and in case of cations as Na+ > K+. The data pertaining to adsorption of Zn conformed to Freundlich and Langmuir adsorption equations both for the anions and cations. The averaged values of the distribution coefficient (Kd) and partial molar free energy change () were greater in the presence of SO4 2– followed by Cl– and NO3 –, and these values were more in the presence of Na+ as compared to K+. The bonding energy constant and Freundlich constant (K) were also determined.