Journal of Soil Biology
Year:2019 | Volume:7 | Issue:1 |Papers Count:8

Soil tillage method and plant residue management are two important agricultural practices which affect soil properties, fauna population and crop production. A 3-year field experiment was conducted to evaluate the effects of tillage methods (conventional tillage (CT), reduced tillage (RT), and No-Till (NT)) and wheat residue management (residue removal and retention) on earthworm population, infiltration process, organic carbon (OC), and corn yield at Zarghan, Fars province. The experimental design was a split-plot with three replications. The highest kernel yield (14447 kg ha-1) and harvest index (36. 82%) of corn were obtained by RT and CT methods when residue returned, respectively. Applying RT method accompanied by keeping residue increased corn yield up to 30% compared to NT method. Organic carbon decreased by CT method and residue removal at 15 and 12% in the soil depth ranges of 0-10 and 10-20 cm compared to conservation tillage, respectively. The highest water infiltration process into the soil was achieved by RT and CT methods compared to NT method when residue returned. The highest earthworm population was obtained by NT method and residue retention, while earthworm population decreased by CT method and residue removal at 38. 5 and 50% compared to RT and NT methods, respectively. It is concluded that, to grantee the corn yield potential and improve earthworm activity and soil fertility under wheat-corn rotation, adopting RT method accompanied by keeping wheat residue (standing residue with a height of 30 cm), is recommended.

Pseudomonas bacteria are the most important plant growth promoting rhizobacteria due to their widespread distribution in soil, their potential to colonizemany plant roots and possessing different plant growth promoting characteristics. The present study aimed to identify isolates of Pseudomonas fluorescens strains of olive tree rhizosphere in saline gardens of Qazvin province. Plant growth promoting characteristics of fifteen isolates of Pseudomonas fluorescens strains such as siderophore, auxin, hydrogen cyanide, ACC deaminase enzyme production, phosphorus solubility in liquid medium, pH changes and salt tolerance (NaCl, MgCl2and CaCl2) (100, 200, 400 mM) were evaluated. Results showed that the dominant strains in producing ACC deaminase were Q7 and Q9, respectively. The Q2 strain was the best one to enhance the production of auxin (11. 96 µ g. ml-1). The solubility of phosphorus in conjunction with pH showed a negative correlation and the highest amount of dissolved phosphorus was related to Q13 (251) isolate. Also, the half of strains (40%) was not able to produce HCN. Commonly, all studied strains were able to produce siderophore after two, four and six days of incubation. Expect Q1 and Q8, other strains were able to grow in the considered salt concentrations. Based on the results, we concluded that some of these strains can be targeted for genomics studies to improve salt stress resistance in plants and orchards under saline soils conditions.

A greenhouse experiment was conducted in a completely randomized design with factorial arrangement to investigate the influence of biological treatments (Pseudomonas fluorescens, Micrococcus yunnanensis, Claroideoglomus etunicatum and Funneliformis mosseae) on Vetiver grass grown on a crude oil contaminated calcareous soil (0, 2 and 4% crude oil). Results showed that the shoot and root dry weight and root colonization decreased in crude oil treatments. While the microbial respiration and total hydrocarbon concentration in post-harvest soil increased significantly. Soil inoculation with Micrococcus yunnanensis and Funneliformis mosseae had a positive effect on shoot dry weight but not for Pseudomonas fluorescens treatment. Iron concentration and iron and zinc concentrationsenhanced significantly in Claroideoglomus etunicatum and Funneliformis mosseaetreatments respectively. Root colonization also increased when mycorrhiza inoculation applied to soil samples. Micrococcus yunnanensis and Funneliformis mosseae increased microbial soil respiration and total hydrocarbon content reduced in post-harvest soil. Our result showed that among tested microorganisms, Micrococcus yunnanensis and Funneliformis mosseae had more positive effects on bioremediation and plant growth in crude oil contaminated calcareous soil.

Collembola along with mites are dominating in soils. In this research, the population of Entomobryomorpha was evaluated in three different ecosystems; field crop, oak forest and grassland in three cities (Eslamabad-e-Gharb, Paveh and Sare pol-e-zahab). Sampling was done every month from June 2016 to May 2018. In each site, ten soil samples were taken from a surface area of 100 cm2 with depth of 13 cm. Then, the population of collembolan was counted to species level. Temperature and moisture content of soil samples were also evaluated simultaneously. The relationship between presence/absence of species and habitat conditions was compared using logistic regression based on temperature and humidity. Totally, 16 species were identified that oak forest had higher species (average 79. 2%) than other ecosystems in three different cities. The highest frequency percentage of springtails was in oak forest in Eslamabad-e-Gharb and Sare pol-e-zahab (60. 77% and 69. 22% respectively) and in Paveh, grassland had a higher frequency than field crop and oak forest (49. 19 %). The results of monthly counting and habitat suitability modeling showed that the abundance population of the most species was occurred in November to May. Most Species frequency was correlated with soil moisture but it had an inverse relationship with soil temperature. However, some species such as Seira sp was presented in low humidity (6% in field crop and 8% in grassland) and high temperature (35 to 40 ċ ). It indicates that not only soil temperature and soil moisture affect population size of soil arthropods but also other environmental factors might be effective in it.

Endophytic fungi increase plant growth and confer stress resistance to plants with different mechanisms. In order to identify endophytic fungiof Pistacia vera and to evaluate their growth promoting and biocontrol properties, samples were taken fromthe leaves and fruits of Pistacia vera in Rafsanjan. After morphological and molecular identification, Growth stimulating factors were evaluated by estimating auxin production, siderophore production and inorganic phosphate solubilizing activity. Biocontrol activities were evaluated based on chitinase and hydrogen cyanide production. Mean comparison of the data showed that the highest amounts of auxin at levels of 0 and 50 mg/L of tryptophan were produced with Trichoderma atroviride TA2-2-1as the amount of 19. 34 and 32. 88 mg/L, respectively. Quambalaria cyanescens QC11-3-2 produced the highest amount of siderophore which the ratio of the diameter of the halo zone to the colony was 2. 96. Only, Byssochlamys nivea BN1-1-1had the ability to solubilize the inorganic phosphate which the ratio of the halo zone diameter to the colony diameter was 1/1. Most chitinase activities were observed by Trichoderma harzianum TH 5-1-2 (2. 92 U/mL) and T. atroviride TA2-2-1 (2. 34 U/mL), respectively. T. atroviride TA2-2-1 and Clonostachys rosea CR2-3-1 were able to produce the HCN.

Cadmium (Cd) is known as one of the most dangerous elements for living organisms, and because of its easy availability for plant, is a major threat for the human food chain. In order to evaluate the effect of adding bio-fertilizers and inoculation of plant growth promoting rhizobacteria (PGPR) such as Micrococcus yunnanensis on chemical forms of soil cadmium, a greenhouse experiment was conducted with a factorial arranged in a completely randomized design with three replications. Treatments consisted of two levels of bacteria (with and without inoculation), four levels of Cd (control, 10, 20, and 40 mg kg-1), and three moisture levels (100, 80, and 65% of field capacity). After corn harvesting, amount of chemical forms of Cd were evaluated. Results indicate that increasing Cd levels significantly increased amount of all chemical forms of Cd. Application of bacteria decreased exchangeable (Ex), carbonate-bound (Car), organic-bound (Om), amorphous iron oxides-bound (AFe-ox) and manganese oxides-bound (Mn-ox) fractions but increased residual (Res) fraction. Reduction of soil moisture decreased Om and AFe-ox bound fractions in not inoculated treatments, but increased AFe-ox and Mn-ox fractions in inoculated soils. Highest contents of Cd were associated with Car-bound fraction, with the order being: Res > Mn ox-bound > AFe-ox-bound > Om-bound > Ex fractions.

Some beneficial soil microorganisms can reduce salt stress in many crops. Two experiments were carried outto study the effect of salinity and microorganisms on the growth characteristics of Plantago ovata Forsk. In the first experiment, tolerant species of phosphate-soluble bacteria screened in a salinity stress condition, a number of bacteria were subjected to semi-quantitative phosphate solubility test. The superior isolate was identified as Pseudomonas fluorescens based on the sequence 16S rRNA gene and other phylogenetic analysis. The second experiment was a factorial experiment in randomized complete block design with three replications. The first factor was three levels of salinity (2. 5, 5 and 10 dS/m), the second factor was mycorrhizal fungus including Funneliformis mosseae, Rhizophagus intraradices and Glomus fasciculatum, and the third factor consisted of two levels of non-bacterial and bacterial application. Shoot and root dry weight, root to shoot dry weight ratio, mycorrhizal growth response and root colonization percentage were measured. Analysis of variance showed that interaction of salinity stress and mycorrhizal fungus on shoot dry weight was significant at level 1% probability. The interaction of salinity stress and bacteria on the ratio of root dry weight to shoot was significant at 5% probability level. The highest root dry weight and root/shoot ratio (1. 7 and 0. 9 respectively) were obtained at 2. 5 dS/m + Glomus fasciculatum treatment. The highest mycorrhizal growth response percentage was 76. 7% at 10 dS/m + Rhizophagus intraradice treatment. Comparison of the mean interactions between salinity stress and bacteria showed that the highest mycorrhizal growth response percentage was obtained in the 10 dS/m salinity + Pseudomonas fluorescenstreatment (45. 6%). The results also showed that salinity decreased the yield of Isabgol, but the simultaneous application of PSB and AMF could compensate the negative effects of salinity stress. According to the results, it is possible to use the simultaneous application of Pseudomonas fluorescens and Rhizophagus intraradices to maximize the production of Plantago ovata Forsk.

Elemental and microbial enrichment of compost are basic solutions to increase its quality. The addition of beneficial bacteria and plant growth promoters are confirmed by various environmental aspects. The pH of compost is a critical factor affecting bacterial persistence. In this study, the municipal compost was sterilized and divided into two parts: compost with initial pH (5. 6) and compost with pH adjusted to 7 by calcium carbonate addition. Incubation of compost with Enterobacter cloacae was performed with 109 CFU g-1 population. The moisture content of the compost adjusted to about 40% of the water holding capacity and the samples were kept in an incubator at 26 ° C. The microbial counting and pH measurement were accomplished at 3, 15, 45, 75, 105, 135, 165 and 195 days after inoculation. The results of microbial counting showed that the effect of pH on bacterial viability in the compost was significant (p<0. 01). Forty-five days after inoculation, the microbial count in non-amended compost declined to about 104 CFU g-1 while in the amended compost it was 109 CFU g-1. Regardless of the fluctuations of microbial population in non-amended compost, the bacterial population was 107 CFU g-1 in both divisions of compost after 135 days' incubation. The number of bacteria in amended and non-amended composts was below the standard limit (106 CFU g-1) after 165 and 140 days incubation, respectively.