JWSS - Journal of Water and Soil Science

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A great number of studies have been conducted on the role of Azotobacter - a free living N₂-fixer - in agricultural soils, but our information is lacking on the importance of Azotobacter in pasture soils. This research was conducted to study the relationship between ecological and edaphical factors with the population of the bacteria in soil. Soil samples were taken from two sites in Azarbaidjan (Mishou-dagh and Khadjeh), having different ecology, soils and vegetation types. We investigated also the effect of inoculation of rhizosphere with soil-isolated A. chroococcum on the growth of wheat (Triticum aestivum L. cv. Omid) during 56 days of growth in a pot experiment. The treatments included: 1) inoculation with A. chroococcum (+A), 2) N fertilizer at a rate of 35 mg/Kg as (NH₄)₂SO₄ (+N), 3) +A+N and 4) –A–N as control with four replications. Results showed that the population of Azotobacter chroococcum correlated positively with organic carbon and negatively with soil pH. In soils covered with vegetation the population of bacteria was higher than that in uncovered soils and the highest population of bacteria was found in soil samples collected from the rhizosphere of grass species and the lowest in that of legume species. In inoculation experiment, shoot and, particularly root growth, increased in the order of +N, +A and +A+N in comparison with control (–A–N) plants. These treatments also stimulate uptake and transport of K into shoot. Interestingly, the effect of +A treatment was significantly higher than that of +N and +A+N treatments. The same results were obtained for nitrogen. A higher uptake and particularly transport of K into shoot was attributed to low molecular weight organic molecules produced in inoculated roots and transport K into shoot. Results showed that inoculation with Azotobacter not only enhanced growth and chlorophyll content, but also stimulated uptake and translocation of ions into shoot. The stimulatory impact of inoculation is most likely a general effect that could also be important in micronutrients translocation into shoot.

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  In this research, after optimization of sterilizing cyst and larvae of second stage of Heterodera schachtii, the possibility of using nematode on seedlings of sugar beet (Beta vulgaris L.) in in vitro condition was studied for developing larvae to cyst. For this purpose, non sterile cysts were extracted from infected soil and hatched into zinc chloride solution with concentration of 0.5gl^-1. Then, for preparation of sterile second stage larvae, several sterilizing treatments were used . Mean comparisons were performed between sterilized live larvae number by Duncan's method. Results showed that 70% ethanol for 1 minute followed by 5% sodium hypochlorite for 5 minutes and 0.1% sodium hypochlorite for 20 minutes were the best treatments for disinfecting cysts and larvae, respectively. In the next step, two nematode susceptible sugar beet varieties were applied to produce cyst from the larvae in in vitro culture. PG_oB medium containing different hormonal compositions was used to produce hairy roots and inoculation of seedling with sterilized larvae. After nematode inoculation tests, were the stained cysts were observed under stereomicroscope and counted 40 days later. Five to twelve cysts were formed on the roots of each seedling from two varieties. As a result, it seems that this technique can be used for sugar beet germplasm evaluation to screen nematode resistant genotypes in in vitro controlled condition.

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Although the crucial function of earthworms in improvement of soil physical properties is well -know, but very little is known of the interactive influence of earthworms and organic materials on soil properties such as soil aggregate stability, particularly in arid and semi-arid soils. The low organic matter content and the significant role of earthworms in improving physical properties of arid and semi-arid soils necessitate studying the interactive effects of organic materials and earthworms. Thus, the main objective of this study was to identify the interactive effects of anecic earthworm (Lumbricus terrestris L.) and various organic residues (including alfalfa, compost, mixture of alfalfa and compost and cow dung) on soil aggregate stability expressed as the Mean Weight Diameter (MWD), Geometric Mean Diameter (GMD) and Aggregation Ratio (AR), and furthermore soil Ca and Mg contents. The experiment consisted of a 2×5 factorial treatment organized in a completely randomized design with four replications under controlled greenhouse conditions, lasted for 150 days. Results showed that earthworm inoculation and organic materials addition alone increased significantly all the indices of soil aggregation and aggregate stability, and Ca and Mg contents. However, the combined use of earthworms and organic residues resulted in more stable aggregates. Results indicated that earthworm inoculation in the presence of organic materials resulted in 39, 58, 2, 67, 43 and 74% increases, respectively in MWD, AR, GMD, Ca, Mg and macroaggregates whereas microaggregates were reduced by 13.5% in earthworm-worked soils. We observed a significant relationship (R2=0.945) between soil Ca content and MWD, demonstrating that earthworms apparently excrete calcite that helps bonding clay particles and soil organic matter via cationic (Ca+2) bridging. In summary, results of this study show that the simultaneous applications of anecic earthworms and organic materials may considerably help in improving the structure of arid and semi-arid soils with low carbon level.

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Soil enzymes are the catalysts for important metabolic process functions including the decomposition of organic inputs and the detoxification of xenobiotics. The aim of this research was to determine the pattern of variation in the activities of dehydrogenase, urease, lipase and phosphatase enzymes, determining the number of hetrotrophic and degrading bacteria and measuring the soil respiration and yield plants during the bioremediation of oil contaminated soils. To this aim, the soil deliberately contaminated with crude oil at a 1 and 2 wt% rate and in four treatments including: plant multiflorum (T1), plant multiflorum with mycorrhiza inoculation (T2), plant multiflorum with oil degrading bacteria inoculation (T3), plant multiflorum with mycorrhiza and oil degrading bacteria inoculation (T4) was employed for bioremediation of oil contaminated soil. The above parameters were determined in five stages during bioremediation and ultimately for the yield of plants at the end of this period .The results showed that the activity of urease and hydrogenase anzymes were increased or decreased parallel to contaminant increase and decrease. In contrast, the activity of lipase anzyme was decreased with contaminant increase and increased with contaminant decrease. Therfore, it can be a good choice for monitoring of bioremediation of contaminated soils. The results showed that the number of degrading and hetrotrophic microorganisms were increased by increasing the amount of contamination and the number of degrading and heterotrophic bacteria were decreased parallel to contaminant decreasing especially in those samples treated with mycorrhiza inoculation. The plant yield and amount of degradation of oil compounds were highest in mycorrhiza plus degrading bacteria treatment.