Soil Dehydrogenase Activity Research Articles

Relationships between root growth of Zinnia hybrid “profusion orange” flowers and phytoremediation of oil-contaminated soil

Relationships exist between plant root growth and the phytoremediation of oil-contaminated soils. In a previous study, we demonstrated that zinnia flowers are well suited for the remediation of oil-contaminated soil. In this study, our goal was to quantify the relationship between zinnia root growth and purification of oil-contaminated soils. Three treatments were used: (1) cultivation of zinnia in oil-contaminated soil (contaminated pots), (2) cultivation in non-contaminated soil (non-contaminated pots), and (3) contaminated soil with no cultivation and only irrigation (irrigated pots). Growth of the Zinnia plants, including their roots, was significantly reduced in the contaminated pots compared with the noncontaminated pots. The soil dehydrogenase activity increased between 45 and 90 days after planting in all parts of the contaminated pots, especially the upper parts. The soil total petroleum hydrocarbon (TPH) concentrations in the contaminated pots decreased throughout the study period. Interestingly, the soil dehydrogenase activity increased, and the soil TPH concentration decreased even in lower parts of the pots where there was very little root growth. Therefore, the cultivation of plants can have a remediative effect on oil-contaminated soil even below the depth reached by the plant roots.

Soil carbon dynamics and productivity of rice–rice system under conservation tillage in submerged and unsubmerged ecologies of Eastern Indian Himalaya

Intensive tillage practices along with improper residue management in a rice (Oryza sativa)–rice system (RRS) contributed to soil fatigue and declining productivity in South Asia. Therefore, a 3-year (2013–2015) field study was conducted to assess tillage modification effects on productivity and soil C sequestration under RRS at ICAR- RC for North Eastern Hill Region, Tripura, India. The experimental site represented two different ecologies: unsubmerged (ECO 1) and submerged (ECO 2), with three tillage practices: conventional tillage (CT), reduced tillage (RT) and no-till (NT). Results showed that the cultivation of RRS under RT produced significantly higher grain (8.6–9.4 Mg ha−1) and straw (11.8–12.9 Mg ha−1) yields under both ecologies over those under CT and RT, in addition to recycling the maximum biomass. Soil under RT had lower bulk density (ρb), the highest soil organic carbon (SOC) concentration, pool, sequestration, accumulation, carbon retention efficiency, soil microbial biomass carbon and dehydrogenase activities under both ecologies as compared to CT. A total amount of 1.34 Mg C ha−1 was accumulated under soils of RT over 3 years. The rate of SOC sequestration ranged from 133.6 kg ha−1 year−1 under soils of CT to 444.7 kg ha−1 year−1 under RT in RRS. Thus, cultivation of RRS under RT with effective residue recycling is recommended for higher system productivity and C sequestration under both rice production ecologies of the NEH region of India.

Microbial activity in different soils in response to metribuzin treatment

The effect of metribuzin on soil microorganisms and their enzymatic activity, as well as the amount of metribuzin residues, greatly depend on the type of soil and its physico-chemical properties. A laboratory experiment was set up to determine the effects of metribuzin on different groups of microorganisms and dehydrogenase activity in loamy and sandy soils. The amounts of metribuzin residues in those soils were also determined. The following concentrations were tested: 12.0, 24.0, 120.0 and 1200.0 mg a.i. kg-1soil. Samples were collected 3, 7, 14, 30 and 45 days after metribuzin application. Metribuzin acted inhibitively on total bacteria counts in both types of soil: 6.9% in loamy and 7.9% in sandy soils. Actinomycetes counts decreased over the first 14 days after metribuzin treatment by 15.6% in loamy and 8.1% in sandy soil. However, starting with the 30th post-treatment day, their number either increased or remained at the control level. Fungi counts increased by 6.0% seven days after the application of the two highest concentrations. In sandy soil, fungi counts were significantly reduced by 29%. Metribuzin treatment significantly reduced the activity of dehydrogenase enzyme in both types of soil. Only the highest test concentration applied to the sandy soil showed a stimulating effect (33.2 %). Degradation data showed that the measured amounts of metribuzin decreased over time in both types of soil at all four test concentrations. The results showed that the extracted amounts of metribuzin active ingredient at all its test concentrations were greater in the sandy type of soil. Loamy soil was shown to have a better sorption capacity due to its higher contents of organic matter and clay.

Soil carbon pools and enzyme activities in aggregate size fractions after seven years of conservation agriculture in a rice–wheat system

Decline in soil organic carbon (SOC) due to intensive tillage and removal or burning of crop residues is considered a major threat to maintaining soil quality and meeting future challenges of food production at national and global scales. Adoption of conservation-agriculture practices (no till and residue retention) is necessary to promote soil structural stability and increases in SOC content and enzyme activities. We evaluated the impact of tillage and residue-management practices on yield, soil labile-C pools, aggregate stability and soil enzyme activities after seven cycles of a rice (Oryza sativa L.)–wheat (Triticum aestivum L.) system on the Indo-Gangetic Plain of India. Treatments included four combinations of tillage and crop establishment in rice (main plots), and three combinations of tillage and residue management in wheat (subplots). Irrespective of rice-establishment method, mean grain yield of no-till wheat with rice-residue mulch (NTW+RR) was 9% and 22% higher, respectively, than of conventional-till (CTW) or no-till wheat with no rice-residue mulch. Soil C pools (very labile, labile, less-labile and non-labile) were significantly higher under a no-till dry-seeded rice (NTDSR)–NTW+RR cycle than conventional-till puddled transplanted rice–CTW. Macro-aggregates (>0.25 mm) had higher labile C pools, glomalin content and enzyme activities than micro-aggregates. NTW+RR significantly increased soil C pools within both macro- and micro-aggregates. Compared with CTW, NTW+RR increased soil dehydrogenase, cellulase and alkaline phosphatase activities by 23%, 34% and 14%, and water-soluble organic C by 31%, and increased water-stable aggregates and mean-weight-diameter. NTDSR–NTW+RR increased SOC, enzyme activity, aggregate stability and wheat grain yield. Results indicated that soil labile-C pools across aggregate fractions were the most sensitive indicators of soil quality when determining the effects of changes in management practices. Furthermore, adoption of no till and residue retention may improve sustainability in rice–wheat systems of the Indo-Gangetic Plain.

Биодиагностика состояния окультуренной городской почвы, загрязненной тяжелыми металлами, методами биоиндикации и биотестирования

The biological effects of contamination with nickel and cadmium were evaluated in cultivated urban soil under field conditions. The methods of bioindication and bioassay indicated high toxicity, deterioration in biochemical properties and slow recovery of contaminated soil. Soil dehydrogenase is a sensitive indicator of metal contaminations, which allows identifying the biological effects that occur even in slightly polluted soils. The data obtained by bioindication using soil dehydrogenase activity were consistent with bioassay results. Bioassays revealed acute toxicity of contaminated soil to daphnia Daphnia magna Straus and green algae Scenedesmus quadricauda (Turp.) Breb. The toxic effect increased with an increase in the metal concentration and depended on the added metal. The toxicity of soils contaminated with cadmium was higher compared to nickel throughout the entire study period. Two years after pollution, a decrease of the toxic effect was observed in soil contaminated with nickel, while the toxic effect of cadmium did not decrease with time. Even after an increase of dehydrogenase activity in nickel-contaminated soil, bioassays still indicated its toxicity for the test objects, particularly as regards green algae. The results indicate the preservation of toxic properties and possible negative effects to biota.

Influences of application of slow-release Nano-fertilizer on green pepper growth, soil nutrients and enzyme activity

In order to examine the fertilizer effect of slow-release Nano-fertilizer and its impact on the ecological environment, a cultivation pot experiment was arranged to study the influences of application of slow-release Nano-fertilizer on green pepper growth, soil Nutrients, enzyme activity and microorganisms. The experiment was designed to have four treatments: treatment 1 (blank treatment), treatment 2 (slow-release Nano-fertilizer), treatment 3 (composite chemical fertilizer), treatment 4 (slow-release Nano-fertilizer + compound fertilizer), and each treatment was five parallels. The results were as follows: (1) The application of slow-release Nano-fertilizer can promote the growth of green pepper, but due to the slow effect of fertilizer, the growth of green pepper was not as good as that of chemical fertilizer. (2) Application of slow-release Nano-fertilizer significantly increased soil nutrients, especially alkaline nitrogen, with an increase of 100.0%. (3) Application of slow-release Nano-fertilizer significantly increased soil enzyme activity and soil microbial population. Compared with blank, soil dehydrogenase and catalase activities of treatment 2 increased by 37.4% and 21.3%, respectively, and soil bacteria, actinomycetes and fungi increased by 50%, 72% and 208%, respectively. Application of slow-release Nano-fertilizer can improved soil nutrient, soil enzyme activity and soil microorganism, reduce nutrient loss and improve soil ecological environment, with a good application value.

Carbon sequestration potential of plantation forestry and improvements in soil nutrient status in a subtropical area of northern India

Variability in carbon sequestration efficiency of different tree species in Kahinaur plantation forest of district Mau, Uttar Pradesh, India was evaluated. Moreover, improvement in nutrient status and other physicochemical characteristics of soil due to plantation forest was also taken into consideration. Soils in the plantation forest possessed higher soil organic carbon (SOC), nitrogen, phosphorus and potassium (NPK) than the adjacent waste land soil. However, nutrient status of both plantation and wasteland soil decreased with increasing soil depth and bulk density. The soil microbial biomass carbon (SMBC), soil enzyme activities like soil dehydrogenase activity, acidic and alkaline phosphates and soil respiration were higher in the plantation forest soil as compared to the waste land soil. The highest SMBC (114.47 μg g−1 soil 24 h−1) was reported in plantation forest soil, but only 56.65 μg g−1 soil 24 h−1 in waste land soil. In addition, the activity of soil dehydrogenase (2.74 μg g−1 soil h−1) was also highest in the plantation forest soil. Among the studied tree species, carbon accumulation was found maximum in Prosopis juliflora, Putranjiva roxburghii, Pithecellobium dulce and Artocarpus heterophyllus depicting that these can be recommended as atmospheric carbon reducers for their better potential to sequester and store carbon. The study indicated that afforestation or forest plantation improved SOC, nutrient stock and improved other important soil fertility parameters in the plantation forest soil as compared to the non-forest soil i.e., waste land.

Effect of gasification biochar application on soil quality: Trace metal behavior, microbial community, and soil dissolved organic matter.

Compared to pyrolysis biochar (PBC), gasification biochar (GBC) differs in both composition and surface functionalities due to the use of an oxidizing purging gas. This work compares the effect of using PBC and GBC as soil amendments on the soil properties, trace metal bioavailability, soil microbial activity, and soil dissolved organic matter (DOM). Biochar-driven reduction of bioavailable metals does not necessarily result in a positive impact on the soil microbial growth. The DOM in the soil was strongly related to the soil microbial activity, as revealed by the strong correlation between the soil dehydrogenase activity (DHA) and soil dissolved organic carbon (r = 0.957, p < 0.01). Three identified fluorescent components (C1, C2, C3) in the soil DOM were closely associated with the soil microbial activity, for instance, with a clear positive correlation between the soil DHA and C1 (r = 0.718, p < 0.05) and a significant negative correlation between the total bacterial fatty acid methyl ester content and C3 (r = -0.768, p < 0.05). The bioavailability of Cd and Zn is not only related to the pH and surface functionalities of the biochar, but also to its aromatic carbon and inorganic mineral composition. This study further demonstrates that a fluorescence excitation-emission matrix coupled with parallel factor analysis is a useful tool to monitor changes in the soil quality after application of biochar, which is greatly relevant to the soil biota.

The Alleopathic Compound Luteolin from Peanut Litter Affects Peanut Nodule Formation and the Rhizosphere Microbial Community

Core Ideas Flavonoid luteolin can accumulate in consecutively monocultured peanut fields. Luteolin treatment changes the rhizosphere microbial community of peanut. Flavonoid luteolin in peanut residues may cause continuous cropping obstacles. The flavonoid luteolin is a common flavone released from peanut (Arachis hypogaea L.) residues. Luteolin accumulates in consecutively monocultured soil and affects the growth and nodulation of continuously cropped peanut. A microcosm experiment was performed to determine the effects of luteolin released from peanut residue on peanut nodule formation and on the rhizosphere soil microbial community. Luteolin reached a maximum concentration of 0.42 μg g−1 soil in litterbag experiments, and the half‐life of luteolin at 2.5 to 40 μg g−1 soil varied from 1.13 to 2.91 d. Results from pot experiments indicate that soil with luteolin treatment inhibited peanut seedling nodulation and growth, soil dehydrogenase activity, microbial biomass carbon content, biofilm formation, and chemotactic response of Rhizobium sp. and changed the microbial community structures and abundances at concentration of luteolin as low as 0.42 μg g−1 in soil. This might explain why peanut performs poorly with continuous consecutive monocropping.

Effects of basal fertilizer and perlite amendment on growth of zinnia and its remediation capacity in oil-contaminated soils

ABSTRACTIn a previous study we demonstrated that Zinnia hybrida ‘Profusion White’ can be effective in the remediation of oil-contaminated soil. However, the rates of removal of total petroleum hydrocarbons (TPH) were greatest in soils containing 9000 mg/kg TPH and less in soils with higher concentrations of TPH. This study was conducted to investigate the effects of basal fertilizer rates and perlite amendments on the growth of zinnia and its remediation capacity in soils with TPH concentrations of 26,000 mg/kg. Methodology: Soils were prepared with or without TPH at an initial concentration of 26,194 mg/kg, and then each of these soils was amended with either a basal fertilizer rate with or without 20% perlite, or twice the basal fertilizer rate with or without 20% perlite. Pots were prepared with the following treatments in these soils: contaminated soil planted with zinnia (planted-contaminated), uncontaminated soil planted with zinnia (planted-uncontaminated), and contaminated soil not planted with zinnia (unplanted-contaminated). Plant growth, soil dehydrogenase activity (DHA), and TPH concentrations were analyzed at 30 and 60 days after sowing. Results: Plant growth in oil-contaminated and uncontaminated soils was superior in pots with twice the basal fertilizer and with perlite. The DHA values in the planted-uncontaminated treatments were significantly lower than those in the planted-contaminated and unplanted-contaminated treatments. However, the effects of basal fertilizer amount and perlite on the DHA values of the soils were small. The TPH concentrations in the planted-contaminated soils were significantly lower than those in the unplanted-contaminated soils after 30 and 60 days. Furthermore, the TPH concentrations in the planted-contaminated soils were lowest in pots with twice the basal fertilizer and with perlite. Conclusions: These results show how phytoremediation of soils with high levels of oil contamination by Z. hybrida ‘Profusion White’ can be practically enhanced by amending the soil with perlite and higher basal fertilizer rates.

Dissipation of polycyclic aromatic hydrocarbons (PAHs) in soil amended with sewage sludge and sludge compost

In this study, greenhouse experiments were conducted under the condition of different amendment ratios and planting tall fescue (Festuca arundinacea). The amendment ratios of sewage sludge or sludge compost to soil were of 0, 10, 25, and 50% (w/w). The removal rates of PAH, catalase, and dehydrogenase activities of amended soil and accumulation of PAHs by vegetation were detected to investigate the differences of PAH dissipation in sludge-amended and compost-amended soils. The initial PAH concentrations in three amended soils increased with the more addition of sludge or compost. After 126-day experiment, maximum PAH removal rates were observed in sludge-amended and compost-amended soils with PAH concentration of about 200μgkg-1. And the removal of PAHs showed better efficiencies in compost soil rather than in sludge soil. The more catalase activity and dehydrogenase activity of soil were obtained, respectively, in sludge soil and compost soil. The results indicated that the mechanism of PAH dissipation in two types of amended soils were different. The abundant amount of microorganism dominated PAH dissipation in sludge soils, and PAHs dissipated mainly caused of intense activity of microorganism in compost soils. In addition, PAH accumulation in tall fescue suggested that the transference approach of PAHs was from soil to the roots, and then accumulated in the shoots of tall fescue. It was prone to store up more PAHs in vegetation in the condition of high molar weight of PAHs, more biomass of vegetation, and heavy PAH concentration in soil.

Enhancement of apple (Malus domestica) productivity and soil health through organic fertilization and bio-inoculants under north-western Himalayan region of India

A field experiment was performed to assess the medium-term effect of mineral fertilizer and organic fertilizer (vermicompost) supplemented with microbial inoculants (Azotobacter and Microphos) on growth parameters of apple (Malus domestica Borkh. cv. Oregon Spur) and soil health parameters. Eight different combinations of mineral fertilizer, vermicompost (VC) and microbial inoculants treatments were applied during 2012 to 2014. The percentage increase in trunk cross section area (TCSA) during the three years of experiment was maximum 17.0% and 15.8% with application of 75% of recommended dose of fertilizer (RDF) + 25% N through VC + Microphos and 50% of RDF + 50% N through VC, respectively. The pooled data of three years revealed that, maximum fruit yield (20.8 tonnes/ha) and production efficiency (112 g/cm2 TCSA) of crop were recorded in the treatment received 50% N through VC and this treatment is similar (P ≤ 0.05) with treatment having application of 75% of RDF + 25% N through VC + Microphos while minimum was recorded in control. Among all treatments, application of 50% N through VC and application of 25% N through VC + Microphos performed better for taming chemical fertility of soil. Study also noticed that, continuous three years application of 50% N through VC, the soil organic carbon, soil microbial biomass carbon and dehydrogenase activity of soil increased by 17, 33 and 39%, respectively over control. Overall, study revealed that, plants received 50% of RDF + 50% VC or 25% VC + Microphos had highest ability of promoting the sustainability of apple yield, soil biological and chemical fertility of an agro-ecosystem in north-western Himalayan region.

Improved growth and nutrient acquisition of wheat genotypes in phosphorus deficient soils by plant growth-promoting rhizospheric and endophytic bacteria

ABSTRACTIn this study, two bacterial strains were isolated from the rhizosphere and inside the roots of wheat (Triticum aestivum L.) plants growing in wheat land of Iran. Based on the 16s rRNA gene sequences, strains R185 and E240 were identified as Pseudomonas sp. (rhizospheric isolate) and Pseudomonas mosselii (endophytic isolate), respectively. Isolates were tested for traits that affect plant growth such as indole-3-acetic acid, siderophore, hydrogen cyanide production, and phosphate solubilization ability. Then the effect of strains on growth promotion, protein, nutrients of grains, and soil enzyme activity was investigated using a low-phosphorous soil under greenhouse conditions. Results revealed that significantly higher biomass accumulation and micronutrient assimilation were obtained in all the pots treated with bacterial strains as compared to the control. Co-inoculation of rhizospheric and endophytic bacteria improved the protein of grain by 11.3% (Marvdasht) and 9% (Roshan). Microbial inoculation had a positive effect on the concentration of P, Zn, and Fe in wheat grains. While inoculating wheat genotypes with a single rhizospheric strain increased dehydrogenase activity by 53.4%, this effect became stronger with increasing endophytic strain: up to 72% increase in soil dehydrogenase activity was observed in bacterial consortium treatment. Taken together, inoculation by rhizospheric–endophytic mix-strains with multi-plant growth-promoting traits could be a promising option to promote cereal quality.

Effects of Soil Microbes on Methane Emissions from Paddy Fields under Varying Soil Oxygen Conditions

Core Ideas Improvement in the soil oxygen condition reduced methane emissions from the paddy fields. Methane emissions exhibited two peaks (tillering and booting stage) during rice growth stage. Methane emissions in the paddy field were mainly concentrated prior to the full heading stage. Soil oxygen conditions and rice development stages both affected the diurnal variation of the CH4 fluxes. A two‐year experiment was conducted in southeast China to investigate the effects of microbes at different soil oxygen conditions, including continuous flooding (CF), chemical aeration (CA), and alternate wetting and drying (AWD) on methane (CH4) emissions from paddy fields. Two peaks of seasonal CH4 fluxes appeared at the tillering and booting stages and the first peak was higher than the second. The diurnal CH4 fluxes exhibited one peak during tillering stage and two peaks during booting stage in CF and CA treatments, whereas one peak was observed in AWD treatment. The CA and AWD treatments reduced CH4 emissions but increased rice yield than CF treatment in both years. Compared with CF treatment, the average flux in CA and AWD treatments was reduced by 31.75% and 49.89% in 2015 and by 28.25% and 41.97% in 2016, respectively. The CA and AWD treatments had higher soil redox potentials (Eh), larger methanotrophic pmoA copy numbers, lower soil dehydrogenase activity, lower methanogenic mcrA copy numbers, and lower soil microbial biomass C than CF treatment. Significant positive correlations were observed between the CH4 emissions and the abundance of methanogen, soil dehydrogenase activity, and soil respiration; significant negative correlations were observed between the CH4 emissions and the abundance of methanotrophs, and soil Eh. Our results indicate that an improvement in soil oxygen conditions decreased the abundance of methanogens, increased the abundance of methanotrophs, and improved Eh, thereby contributing to a reduction in the CH4 emissions without affecting rice yield.

Dissipation of herbicides after repeated application in soils amended with green compost and sewage sludge

Certain agricultural practices, such as the repeated application of herbicides or organic amendments to soil, can influence herbicide dissipation. This research has studied the effects of two repeated applications of mesotrione, pethoxamid, and triasulfuron on their dissipation rates in unamended soil (S) and soil amended with green compost (S+GC) or sewage sludge (S+SS). The dissipation experiment has also included an evaluation of the adsorption of the three herbicides by soils and of changes in soil dehydrogenase activity (DHA). The adsorption of the three herbicides by amended soils (Kf range 0.83–2.98) was higher than by unamended soil (Kf range 0.20–0.64). The adsorption coefficients (Kd) of mesotrione and triasulfuron were higher for S+SS, while that of pethoxamid was higher for S+GC, but no relationship between values for the time to 50% degradation (DT50) and adsorption coefficients could be determined. The repeated application of mesotrione decreased its dissipation rate in unamended soil (DT50 increased from 4.75 to 8.15 days) and amended soils (DT50 increased from 11.7 to 28.2 days in S+GC and from 17.7 to 37.9 in S+SS), whereas the repeated application of pethoxamid increased its dissipation rate in all the treatments, and the rate for triasulfuron increased only in amended soils. The highest DT50 values for pethoxamid (12.3 days) and triasulfuron (57.1 days) were in S+GC, and the lowest in S+SS (8.35 and 24.7 days). Soil DHA was stimulated by the presence of GC in the soil and by the first application of mesotrione. The second application of mesotrione and pethoxamid positively affected soil DHA, but this did not occur for triasulfuron. The repeated applications of herbicides and soil organic amendments have different effects on herbicide dissipation, adsorption, and soil DHA, and they should be taken into account when assessing soil quality and other potential environmental implications of pesticide use.

Individual and combined effects of cadmium and polycyclic aromatic hydrocarbons on the phytoremediation potential of Xanthium sibiricum in co-contaminated soil

ABSTRACTSoil contamination with heavy metals and organic pollutants continues to cause major ecological damage and human health problems. Phytoremediation offers a highly promising technology for the recovery of sites contaminated with mixed pollutants. In this study, we performed a greenhouse experiment to investigate the individual and combined effects of cadmium (Cd) and polycyclic aromatic hydrocarbon (PAH) contamination on the growth of Xanthium sibiricum, and also the ability of this species to accumulate and remove Cd and to reduce PAHs over a period of 75 days. Our results demonstrated that individual or combined contamination by Cd and PAHs showed no significant differences to the control treatment except in the high Cd treatment. The reduction of PAH concentration in the soil with the passage of time was similar in the presence or absence of plants. At higher levels of Cd, the removal of pyrene decreased in both planted and non-planted soils; however, this effect might be due to the higher Cd content. Soil dehydrogenase and polyphenol oxidase activities showed that soil contamination did not have a significant effect on the removal of PAHs. Overall, our results suggest that X. sibiricum might be a suitable species for use in the phytoremediation of contaminated soils.

Remediation of saline soils contaminated with crude oil using the halophyte Salicornia persica in conjunction with hydrocarbon-degrading bacteria

The negative impact of salinity on plant growth and the survival of rhizosphere biota complicates the application of bioremediation to crude oil-contaminated saline soils. Here, a comparison was made between the remedial effect of treating the soil with Pseudomonas aeruginosa, a salinity tolerant hydrocarbon-degrading consortium in conjunction with either the halophyte Salicornia persica or the non-halophyte Festuca arundinacea. The effect of the various treatments on salinized soils was measured by assessing the extent of total petroleum hydrocarbon (TPH) degradation, the soil's dehydrogenase activity, the abundance of the bacteria and the level of phytotoxicity as measured by a bioassay. When a non-salinized soil was assessed after a treatment period of 120 days, the ranking for effectiveness with respect to TPH removal was F. arundinacea > P. aeruginosa > S. persica > no treatment control, while in the presence of salinity, the ranking changed to S. persica > P. aeruginosa > F. arundinacea > no treatment control. Combining the planting of S. persica or F. arundinacea with P. aeruginosa inoculation (“bioaugmentation”) boosted the degradation of TPH up to 5–17%. Analyses of the residual oil contamination revealed that long chain alkanes (above C20) were particularly strongly degraded following the bioaugmentation treatments. The induced increase in dehydrogenase activity and the abundance of the bacteria (3.5 and 10 fold respectively) achieved in the bioaugmentation/S. persica treatment resulted in 46–76% reduction in soil phytotoxicity in a saline soil. The indication was that bioaugmentation of halophyte can help to mitigate the adverse effects on the effectiveness of bioremediation in a crude oil-contaminated saline soil.

Effects on Selected Soil Properties of Subsurface Banding and Surface Broadcasting Pelletized Poultry Litter on Cotton

The response of soil chemical, physical, and biological properties to subsurface band and surface broadcast applications of pelletized poultry litter (PPL) to row crops has not been well documented in Mississippi agroecosystems. This study was conducted in a no-till system on Caledonia silt loam and in a conventional tillage system on Marietta loam, to determine the effects of PPL placement relative to inorganic N fertilizer on selected soil health indicators, including total C, penetration resistance, and microbial activity. The experimental design at each site was a randomized complete block with three treatments replicated four times. Treatments were PPL at the rate of 6.7 Mg ha−1, state-recommended inorganic N fertilizer, and an unfertilized control. Inorganic N fertilizer was applied as urea-ammonium nitrate (32% N). Relative to inorganic N fertilizer, applying PPL in subsurface band for 4 years (2010–2103) increased soil P by 48% and total C by 17%. Regardless of the PPL application method, soil penetration resistance was 19% lower with PPL than fertilizer N. Residual NO3-N levels in the soil layers did not differ between PPL and unfertilized control; however, levels were greatest with inorganic N fertilizer. Additionally, applying PPL in subsurface bands increased soil dehydrogenase activity and cephalothin-resistant heterotrophic plate count bacteria as compared with the control and inorganic N fertilizer. Cotton lint yield was significantly greater with PPL than with inorganic N fertilizer in 2012 in Caledonia silt loam soil (1,244 vs. 1,128 kg ha−1) and in 2013 in Marietta loam soil (1,369 vs. 1,078 kg ha−1). Subsurface band placement of PPL appeared to be very useful in improving soil chemical, physical, and biological properties.

Concentration-dependent responses of soil bacterial, fungal and nitrifying communities to silver nano and micron particles.

The growing use of silver nanoparticles (AgNPs) is likely to result in increased environmental contamination. Although AgNPs have been reported to affect microbial communities in a range of ecosystems, there is still a lack of information concerning the effect of low concentrations of AgNPs on soil microbial community structures and functional groups involved in biogeochemical cycling. In this study, the concentration-dependent effects of AgNPs and silver micron particles (AgMPs) on bacterial and fungal community structures in an agricultural pastureland soil were examined in a microcosm-based experiment using enzyme analysis, molecular fingerprinting, qPCR and amplicon sequencing. Soil enzyme processes were impacted by Ag contamination, with soil dehydrogenase activity reduced by 1mgkg-1 of AgNPs and AgMPs. Soil urease activity was less susceptible, but was inhibited by ≥ 10mgkg-1 AgNPs. The significant (P ≤ 0.001) decrease in copy numbers of the amoA gene by 10mgkg-1 AgNPs indicated that archaea ammonia oxidisers may be more sensitive to AgNP contamination than bacteria. Amplicon sequencing revealed the bacterial phyla Acidobacteria and Verrucomicrobia to be highly sensitive to AgNP contamination. A broad reduction in the relative abundance of Acidobacterial genera was observed, with the exception of the genus Geothrix which increased in response to AgNP and AgMP amendment. Broad tolerance to Ag was observed among the Bacteriodetes, with higher relative abundance of most genera observed in the presence of AgNPs and AgMPs. The proteobacterial genus Dyella was highly tolerant to AgNPs and AgMPs and relative abundance of this genus increased with Ag concentration. Soil fungal community structure responded to both AgNPs and AgMPs, but the nanoparticle had an impact at a lower concentration. This study demonstrates that pastureland soil microbial communities are highly sensitive to AgNP amendment and key functional processes may be disrupted by relatively low levels of contamination.

Soil Microbial Activities and Yield of Elephant Foot Yam as Influenced by Weed Management Practices in Alfisols

ABSTRACTWeed infestation causes yield reduction up to 100% in elephant foot yam [Amorphophallus paeoniifolius (Dennst.) Nicolson] due to the widely spaced planting. At present, manual weeding is popular but expensive, tedious, and time-consuming. Herbicides and polythene mulching may be alternative methods for weed management. A field experiment was conducted during May–December 2015 at the Regional Centre of Indian Council of Agricultural Research-Central Tuber Crops Research Institute, Bhubaneswar, Odisha, India, to determine the effects of weed management practices on soil quality, microbial activities, and yield performance of elephant foot yam in an Alfisol under drip irrigation. The treatment involving weed control ground cover (WCGC) resulted in lower weed biomass, greater weed control efficiency (WCE), and greater corm yield (37.4 t∙ha−1) by 335% over the weedy check. The yield with the weed control ground-cover treatment was comparable to yields for four manual weedings at 30, 60, 90, and 120 days after planting (DAP) (33.7 t∙ha−1) and two manual weedings at 30 and 60 DAP along with postemergence application of glyphosate at 90 DAP (32.9 t∙ha−1). Use of WCGC resulted in greater postharvest soil available N, P, K, Fe, Cu, Mn, and Zn, increased populations of fungi, bacteria, and actinomycetes, and soil dehydrogenase, fluorescein diacetate, acid, and alkaline phosphatase activities. Two manual weedings at 30 and 60 DAP, along with the application of glyphosate at 90 DAP, resulted in higher soil organic carbon. WCGC appears to be a good weed management option in elephant foot yam.