Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “SOIL”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 91 records · Page 5Linked to original sources
PubMed2006

Soil factors controlling the expression of copper toxicity to plants in a wide range of European soils.

The impact of soil properties on metal bioavailability to plants is well recognized. However, the effect of soil bioavailability parameters on toxicity threshold values for Cu in plants needs quantification. Eighteen European soils varying widely in soil properties were amended with CuCl2 to obtain a range of seven concentrations including an unamended control. Two plant toxicity assays, barley root elongation (4 d) and tomato shoot growth (21 d after emergence), were performed on each soil under controlled environment conditions. The effective concentration of added Cu causing 50% inhibition (EC50) ranged from 36 to 536 mg/kg soil and from 22 to 851 mg/kg soil for barley root elongation and tomato shoot growth, respectively, representing variation in EC50 among soils of 15- and 39-fold. Single regressions carried out between Cu toxicity threshold values and various soil properties showed that exchangeable calcium and soil cation exchange capacity (CEC; measured at soil pH) were the best single predictors for toxicity values from both plant tests. The inclusion of other soil properties, such as iron oxide concentration, soil pH, clay, or organic carbon content, further improved predictions. For risk assessment, we suggest that Cu toxicity threshold values (EC50) be normalized on the key soil property of CEC. If available, soil exchangeable calcium and iron oxide concentration would improve the normalization.

Agriculture↗
PubMed1998

Association of Chernobyl-derived 239+240Pu, 241Am, 90Sr and 137Cs with different molecular size fractions of organic matter in the soil solution of two grassland soils.

Radiocesium is normally bound only rather weakly and unspecifically by humic substances, in contrast to the actinides Pu and Am. Recently, however, it was observed that fallout 137Cs in the soil solution from an Of-horizon of a podzol forest soil (slightly decomposed plant material) was associated essentially only with one single size fraction of the humic substances. In deeper soil layers with well humified material (AOh-horizon), radiocesium was associated with all size fractions of the dissolved organic matter (DOM). To examine whether this unexpected behaviour is also observable for DOM isolated from other soils, we determined the association of fallout 137Cs, 90Sr, 238Pu, 239+240Pu and 241Am with various size fractions of DOM from in situ soil solutions isolated from two layers (0-2 cm and 2-5 cm) of two grassland soils (a soddy podzolic soil and a peat soil) within the 10 km zone of the nuclear reactor at Chernobyl (Ukraine). The four size fractions of DOM as obtained by gel filtration of the soil solution were (mean nominal molecular weight in daltons): fraction I: > or = 2000, fraction II: 1300; fraction III: 560, fraction IV: inorganic compounds. The results for the well humified DOM (humus accumulation horizon of podzol, deeper layer of peat soil) showed that Pu and Am are essentially associated with the high molecular weight fractions, while Sr is present only in the 'inorganic' fraction. Radiocesium is found in all the size fractions separated. A quite similar pattern was also found for Pu, Am, and Sr in the soil solution from only slightly decomposed plant material (0-2 cm of peat soil), but not for radiocesium. This radionuclide was again essentially only observable in one single low molecular weight fraction of DOM. The above results thus support our recent observations in the different horizons of a forest podzol mentioned above, even though no reason for the different binding of radiocesium by well humified soil organic matter and by only slightly decomposed plant material can be given at present. The data demonstrate, however, that information on only the total amount of a radionuclide in the soil solution will not be sufficient to interpret or predict its fate adequately in the soil.

Americium↗
PubMed2006

Grass mulching effect on infiltration, surface runoff and soil loss of three agricultural soils in Nigeria.

Mulching the soil surface with a layer of plant residue is an effective method of conserving water and soil because it reduces surface runoff, increases infiltration of water into the soil and retard soil erosion. The effectiveness of using elephant grass (Pennisetum purpureum) as mulching material was evaluated in the laboratory using a rainfall simulator set at rainfall intensities typical of the tropics. Six soil samples, two from each of the three major soil series representing the main agricultural soils in South Western Nigeria were collected, placed on three different slopes, and mulched with different rates of the grass. The surface runoff, soil loss, and apparent cumulative infiltration were then measured under each condition. The results with elephant grass compared favorably with results from previous experiments using rice straw. Runoff and soil loss decreased with the amount of mulch used and increased with slope. Surface runoff, infiltration and soil loss had high correlations (R = 0.90, 0.89, and 0.86, respectively) with slope and mulch cover using surface response analysis. The mean surface runoff was correlated negatively with sand content, while mean soil loss was correlated positively with colloidal content (clay and organic matter) of the soil. Infiltration was increased and soil loss was reduced greatly with the highest cover. Mulching the soils with elephant grass residue may benefit late cropping (second cropping) by increasing stored soil water for use during dry weather and help to reduce erosion on sloping land.

Agriculture↗
PubMed2005

Spatial and temporal variations in soil respiration in relation to stand structure and soil parameters in an unmanaged beech forest.

Soil CO2 efflux (soil respiration) plays a crucial role in the global carbon cycle and efflux rates may be strongly altered by climate change. We investigated the spatial patterns of soil respiration rates in 144 measurement locations in a 0.5-ha plot and the temporal patterns along a 300-m transect in the 0.5-ha plot. Measurements were made in an unmanaged, highly heterogeneous beech forest during 2000 and 2001. We investigated the effects of soil, roots and forest stand structure on soil respiration, and we also assessed the stability of these spatial patterns over time. Soil temperature alone explained between 68 and 95% of the temporal variation in soil respiration; however, pronounced spatial scatter of respiration rates was not explained by soil temperature. The observed spatial patterns stayed remarkably stable throughout the growing season and over 2 years. The most important structural parameter of the stand was the mean diameter at breast height of trees within a distance of 4 m of the measurement locations (m-dbh4), which explained 10-19% of the variation in soil respiration throughout the growing season. Among the soil chemical parameters, carbon content (bulk as well as dissolved) and magnesium content explained 62% of the spatial variation in soil respiration. The final best model combining soil, root and stand structural parameters (fine root biomass, soil carbon content, m-dbh4 and soil water content) explained 79% of the variation in soil respiration, illustrating the importance of both biotic and abiotic factors.

Carbon Dioxide↗
PubMed2006

Soil and surface runoff phosphorus relationships for five typical USA midwest soils.

Excessively high soil P can increase P loss with surface runoff. This study used indoor rainfall simulations to characterize soil and runoff P relationships for five Midwest soils (Argiudoll, Calciaquaoll, Hapludalf, and two Hapludolls). Topsoil (15-cm depth, 241-289 g clay kg(-1) and pH 6.0-8.0) was incubated with five NH4H2PO4 rates (0-600 mg P kg(-1)) for 30 d. Total soil P (TPS) and soil-test P (STP) measured with Bray-P1 (BP), Mehlich-3 (M3P), Olsen (OP), Fe-oxide-impregnated paper (FeP), and water (WP) tests were 370 to 1360, 3 to 530, 10 to 675, 4 to 640, 7 to 507, and 2 to 568 mg P kg(-1), respectively. Degree of soil P saturation (DPS) was estimated by indices based on P sorption index (PSI) and STP (DPSSTP) and P, Fe, and Al extracted by ammonium oxalate (DPSox) or Mehlich-3 (DPSM3). Soil was packed to 1.1 g cm(-3) bulk density in triplicate boxes set at 4% slope. Surface runoff was collected during 75 min of 6.5 cm h(-1) rain. Runoff bioavailable P (BAP) and dissolved reactive P (DRP) increased linearly with increased P rate, STP, DPSox, and DPSM3 but curvilinearly with DPSSTP. Correlations between DRP or BAP and soil tests or saturation indices across soils were greatest (r > or = 0.95) for FeP, OP, and WP and poorest for BP and TPS (r = 0.83-0.88). Excluding the calcareous soil (Calciaquoll) significantly improved correlations only for BP. Differences in relationships between runoff P and the soil tests were small or nonexistent among the noncalcareous soils. Routine soil P tests can estimate relationships between runoff P concentration and P application or soil P, although estimates would be improved by separate calibrations for calcareous and noncalcareous soils.

Midwestern United States↗
PubMedDate not supplied

Effect of Azospirillum brasilense inoculation on urease activity in soil and gamma-sterilized soil.

Azospirillum spp. is considered a PGPR (plant growth promoting rhyzobacteria) bacterium, besides this interest, there is little information about its effects on other functional microbial groups or on soil enzymes. In this paper, the impact that A. brasilense 7001 inoculation has on urease activity expression in a Typic Argiudoll was studied. Evolution of urease activity of soil and of gamma-irradiation (25 KGy) sterilized soil, and the inoculated strain survival were tested. The relation between soil urease activity and soil NH4(+)-N was also determined. In gamma-sterilized soil, urease activity of inoculated soil increased with time, showing significant differences with regard to the control soil without inoculum at day 15. In non-sterile soil, urease activity decreased during the studied period in all treatments; in inoculated soil, it showed higher or lower values than the control depending on sampling time. Azospirillum survival was important and different according to soil conditions. The negative relation between NH4(+)-N concentration and soil urease activity (r2 = 0.62) was not observed in inoculated soil. The role of the addition of autoclaved inoculum in the urease activity expression is discussed. The research proves that in both studied situations Azospirillum modified soil urease activity, and that the competition with native microorganisms and soil NH4(+)-N may affect this bacterium capacity.

Azospirillum brasilense↗
PubMed2002

[Effect of returning corn straw into soil on soil fertility].

Three-year field micro-plot experiment was conducted to study the effect of applying corn root stubble, corn straw, and the ordure of cattle fed with corn straw to improve soil fertility in northern Liaoning province. The results showed that chemical fertilizers could significantly increase the corn production, while organic fertilizers mainly improved the soil physical and chemical properties so as to increase soil fertility. In comparison with no fertilizer treatment, combination of chemical fertilizers and organic materials could increase soil organic matter by 3.06%-27.78%. The increments of soil organic matter by using different organic materials were in order of 100% corn straw > 50% corn straw > mixture of cattle ordure and soil > cattle ordure > 33% corn straw > corn root stubble. For maintaining and increasing soil organic matter, corn straw was better than mixture of cattle ordure and soil, and secondly better than cattle ordure if they contained the same carbon content. In addition, comparing with applying chemical fertilizers only, combination of chemical fertilizers and organic materials increased soil labile oxidization organic matter by 10.91%-20.67%, increased extractable humic acid by 1.43%-14.28%, raised slack/stable ratio of bonded humus by 0.07-0.19, and raised HA/FA ratio by 0.07-0.24. Meanwhile, this combination improved the soil nutrient status of N, P, and K, and the status of soil moisture and porosity, which demonstrated the increase of activity of soil organic matter and the improvement of soil fertility. So directly adding straw into soil without removing after harvest in autumn should be actively recommended, and the amount of corn straw added into soil should be 30 to 50 percent of the total production of corn straw.

Fertilizers↗
PubMed2003

[Effects of soil temperature and moisture on soil respiration in different forest types in Changbai Mountain].

The effects of soil temperature (0, 5, 15, 25, 35 degrees C) and water content on soil respiration in three forest types in Changbai Mountain were evaluated in laboratory condition. The results indicated that the soil respiration rate was positively correlated to soil temperature from 0 to 35 degrees C and it increased with soil water content from 0.21 to 0.37 kg.kg-1. The soil respiration rate decreased with soil water content when water content was over the range. The result suggested the interactive effects of temperature and water content on soil respiration. There were significant differences in soil respiration among the various forest types and the highest was in broad leaf Korean pine forest, then in erman's birch forest, and it was the lowest in dark coniferous forest. The optimal condition for soil respiration in broad-leaved Korean pine forest was at 35 degrees C under 0.37 kg.kg-1 water content, and it was at 25 degrees C under 0.21 kg.kg-1 in dark coniferous forest and at 35 degrees C under 0.37 kg.kg-1 water content in erman's birch forest. Because the forests of broad leaf Korean pine, dark coniferous and erman's birch are located at various altitudes, the soil temperatures had 4-5 degrees C variation in different forest types during the same period. The soil respiration rates measured in brown pine mountain soil were lower than those in dark brown forest and they were higher in mountain grass forest soil than those in brown pine mountain soil.

Carbon Dioxide↗
PubMed2005

Soil identification and chemometrics for direct determination of nitrate in soils using FTIR-ATR mid-infrared spectroscopy.

The use of mid-infrared attenuated total reflectance (ATR) spectroscopy enables direct measurement of nitrate concentration in soil pastes, but strong interfering absorbance bands due to water and soil constituents limit the accuracy of straightforward determination. Accurate subtraction of the water spectrum improves the correlation between nitrate concentration and its nu3 vibration band around 1350 cm(-1). However, this correlation is soil-dependent, due mostly to varying contents of carbonate, whose absorbance band overlaps the nitrate band. In the present work, a two-stage method is developed: First, the soil type is identified by comparing the "fingerprint" region of the spectrum (800-1200 cm(-1)) to a reference spectral library. In the second stage, nitrate concentration is estimated using the spectrum interval that includes the nitrate band, together with the soil type previously identified. Three methods are compared for estimating nitrate concentration: integration of the nitrate absorbance band, cross-correlation with a reference spectrum, and principal component analysis (PCA) followed by a neural network. When using simple band integration, the use of soil specific calibration curves leads to determination errors ranging from 5.5 to 24 mg[N]/kg[dry soil] for the mineral soils tested. The cross-correlation technique leads to similar results. The combination of soil identification with PCA and neural network modeling improves the predictions, especially for soils containing calcium carbonate. Typical prediction errors for light non-calcareous soils are about 4 mg[N]/kg[dry soil], whereas for soils containing calcium carbonate they range from 6 to 20 mg[N]/kg[dry soil], which is less than four percent of the concentration range investigated.

Aluminum Silicates↗
PubMed2005

The influence of soil pollution on soil microbial biomass and nematode community structure in Navoiy Industrial Park, Uzbekistan.

The effects of ammonium-rich and heavy-metal air pollution produced by the industrial enterprises at Navoiy (Uzbekistan) on soil free-living nematodes and microbial population activities was investigated in soil samples collected in a 5-km radius surrounding the industrial enterprises. At each location (n=4), soil samples were collected from the upper layer (0-10 cm) for determination of soil moisture (SM), total organic carbon (C(org)), total soluble nitrogen (TSN), soil electrical conductivity (EC) and cations (Ca(2+), K(+), Na(+)). Heavy metals (As, Cu, Pb, Zn), soil basal respiration (BR), microbial biomass (C(mic)) and nematode populations were determined. The highest level of TSN was found near the industrial enterprises, with 23.8 and 24.0 mg/kg at NavoiAzot and NavoiGRES, respectively. Soil sample pH was found to be weakly alkaline, with levels ranging between 7.9 and 8.1. Mean soil moisture content varied from 0.75% to 0.93% of the wet weight, without any significant differences between the sampling stations. The heavy metals As, Cu, Pb and Zn were accumulated in the upper soil layer. A significant difference was found between soil heavy-metal content for Cu (p<0.0005) and As (p<0.02). Basal respiration and microbial coefficient (C(mic)/C(org)) were found to be significantly negatively correlated with Cu and As soil content. A significantly positive correlation was found between the Cd concentration and the metabolic quotient (qCO(2)) (p<0.003). No significant correlation was observed between the soil microbial population and total soluble nitrogen. Furthermore, the qCO(2), which is a known ecophysiological index for the soil microbial population, was found to be correlated with the total number of nematodes in general and with the bacteriovore-feeding group in particular. No significant correlation was observed between the soil microbial population and total soluble nitrogen.

Animals↗
PubMed2004

PCB in soils and estimated soil-air exchange fluxes of selected PCB congeners in the south of Sweden.

PCB concentrations were studied in different soils to determine the spatial variation over a region of approximately 11 000 km(2). PCB congener pattern was used to illustrate the spatial differences, as shown by principal component analysis (PCA). The relationship to different soil parameters was studied. PCB concentrations in soil showed a large variation between sampling-areas with median concentrations ranging between 2.3 and 332 ng g(-1) (dw). Highest concentrations were found at two sites with sandy soils, one with extremely high organic carbon content. Both sites were located on the west coast of southern Sweden. Soils with similar soil textures (i.e. sandy silt moraine) did not show any significant differences in PCB concentrations. PCB congener composition was shown to differ between sites, with congener patterns almost site-specific. PCB in air and precipitation was measured and the transfer of chemicals between the soil and air compartments was estimated. Soil-air fugacity quotient calculations showed that the PCBs in the soil consistently had a higher fugacity than the PCBs in the air, with a median quotient value of 2.7. The gaseous fluxes between soil and air were estimated using standard modelling equations and a net soil-air flux estimated by subtracting bulk deposition from gaseous soil-air fluxes. It was shown that inclusion of vertical sorbed phase transport of PCBs in the soil had a large effect on the direction of the net soil-air exchange fluxes.

Air Pollutants↗
PubMed2001

Mobility of heavy metals as related to soil chemical and mineralogical characteristics of Brazilian soils.

In order to better understand the relationship between soil characteristics and mobility of some heavy metals, correlation studies were conducted in samples of unlimed and limed A, B and C horizons of three Brazilian soils, representative of the majority of the tropical soils. A number of chemical and mineralogical characteristics of one Oxisol and two Ultisols were related to the retardation factors (Rf) for zinc (Zn), cadmium (Cd), copper (Cu) and lead (Pb). The retardation factors, obtained in leaching column experiments, were used as an estimate of solute movement in the profile. Soil types and soil horizons were found to influence metal retardation factors which, in turn, correlated better with the chemical than the mineralogical soil characteristics. For the unlimed soil samples, the soil characteristics that significantly correlated with Zn-Rf and Cd-Rf were the sum of exchangeable bases (SB), and soil exchangeable (Ca-KCl) and non-exchangeable (Ca-HCl) calcium contents. These results showed the strong influence of the cation exchange phenomenon on the retention and mobility of these two metals. For Cu and Pb, not only SB, cation exchange capacity (CEC) and Ca-KCl and Ca-HCl but also the organic matter correlated well with the Rf, showing that complex or chelate formation may play an important role in the movement of these elements. The important soil chemical characteristics related to the retardation factors in the limed soil samples were SB for Cd, and Ca-HCl for Cu and Pb, suggesting that precipitation may also influence the mobility and retention of the latter two heavy metals in these soil samples. Soil pH influenced the heavy metals adsorption and movement as shown by the significant correlation with the retardation factors when the combined data for the unlimed and limed soil samples was considered.

Adsorption↗
PubMedDate not supplied

Analysis of soils to demonstrate sustained organic carbon removal during soil aquifer treatment.

Soil samples from column studies using five soil types and from a field site were analyzed to assess the ability of soil aquifer treatment to sustain removal of organic carbon. The soil types used in the column studies were chosen to represent a wide range of soil properties that might be used for soil aquifer treatment. Soil samples were analyzed for total organic matter, and a subset of samples was sequentially extracted to determine the effects of soil aquifer treatment. For both column studies and the field site, no accumulation of organic matter was observed below a depth of 8 cm. Near the surface, biological activity at the soil-water interface resulted in an accumulation of biomass and associated organic matter. For the column studies, the accumulation of organic matter in the top 8 cm of soil was <20% of the total organic matter applied to the columns. Soils at depths greater than 8 cm had total organic matter levels less than the original soils before soil aquifer treatment. Significant changes in extractable iron and manganese oxides were observed at the field site, which had been in operation for >10 yr with extended periods of low redox conditions. However, these changes had no apparent effect on the removal of organic carbon in the system. This study provides evidence that soil aquifer treatment can remove organic carbon without accumulation from adsorption that might eventually lead to breakthrough.

Adsorption↗
PubMed1998

Rapid atrazine mineralisation in soil slurry and moist soil by inoculation of an atrazine-degrading Pseudomonas sp. strain.

The evaluation of pesticide-mineralising microorganisms to clean-up contaminated soils was studied with the widely applied and easily detectable compound atrazine, which is rapidly mineralised by several microorganisms including the Pseudomonas sp. strain Yaya 6. The rate of atrazine removal was proportional to the water content of the soil and the amount of bacteria added to the soil. In soil slurry, 6 mg atrazine kg soil-1 was eliminated within 1 day after application of 0.3 g dry weight inoculant biomass kg soil-1 and within 5 days when 0.003 g kg soil-1 was used. In partially saturated soil (60% of the maximal water-holding capacity) 15 mg atrazine kg soil-1 was used. In unsaturated soil, about 60% [U-ring-14C] atrazine was converted to 14CO2 within 14 days. Atrazine was very efficiently removed by the inoculant biomass, not only in soil that was freshly contaminated but also in soil aged with atrazine for up to 260 days. The bacteria exposed to atrazine in unsaturated sterile soil were still active after starvation period of 240 days: 15 mg newly added atrazine kg soil-1 was eliminated within 5 days.

Atrazine↗
PubMed2006

Influence of lead acetate on soil microbial biomass and community structure in two different soils with the growth of Chinese cabbage (Brassica chinensis).

A greenhouse pot experiment was conducted to evaluate the impact of different concentrations of lead acetate on soil microbial biomass and community structure during growth of Chinese cabbage (Brassica chinensis) in two different soils. The field soils were used for a small pot, short-term 60-day growth chamber study. The soils were amended with different Pb concentrations, ranging from 0 to 900mgkg(-1) soil. The experimental design was a 2 soilx2 vegetation/non-vegetationx6 treatments (Pb)x3 replicate factorial experiment. At 60 days the study was terminated and soils were analyzed for microbial parameters, namely, microbial biomass, basal respiration and PLFAs. The results indicated that the application of Pb at lower concentrations (100 and 300mgkg(-1)) as lead acetate resulted in a slight increase in soil microbial biomass, whereas Pb concentrations >500mgkg(-1) caused an immediate gradual significant decline in biomass. However, the degree of impact on soil microbial biomass and basal respiration by Pb was related to management (plant vegetation) or the contents of clay and organic matter in soils. The profiles of 21 phospholipid fatty acids (PLFAs) were used to assess whether observed changes in functional microbial parameters were accompanied by changes in the composition of the microbial communities after Pb application at 0, 300 and 900mg Pbkg(-1) soil. The results of principal component analyses (PCA) indicated that there were significant increases in fungi biomarkers of 18:3omega6c, 18:1omega9c and a decrease in cy17:0, which is an indicator of gram-negative bacteria for the high levels of Pb treatments In a word, soil microbial biomass and community structure, therefore, may be sensitive indicators reflecting environmental stress in soil-Pb-plant system. However, further studies will be needed to better understand how these changes in microbial community structure might actually impact soil microbial community function.

Biomass↗
PubMedDate not supplied

Soil enzyme activities as biological indicators of soil health.

Soil health can be defined as the continued capacity of a specific kind of soil to function as a vital living system, within natural or managed ecosystem boundaries, to sustain plant and animal productivity, to maintain or enhance the quality of air and water environments, and to support human health and habitation. Because of the conflicting pressures increasingly applied to the soil, it is clear that relevant indicators are urgently needed to assess and monitor soil health. Biological indicators of soil health offer certain advantages over physicochemical methods. Among the various biological indicators that have been proposed to monitor soil health, soil enzyme activities have great potential to provide a unique integrative biological assessment of soils and the possibility of assessing the health of the soil biota. Besides, soil enzyme activities provide an easy, relatively rapid, and low cost procedure to monitor soil health. Nevertheless, soil enzyme activities also present some limitations and must always be considered in conjunction with other biological and physicochemicals measurements if we are to diagnose soil health correctly.

Biodegradation, Environmental↗
PubMed1998

Effect of Soil Texture and Soil Sterilization on Susceptibility of Ovipositing Grasshoppers to Beauveria bassiana

The effect of conidial concentration, soil texture, and soil sterilization on the efficacy of Beauveria bassiana against ovipositing grasshoppers (Melanoplus sanguinipes) was investigated in a controlled environment. In the first experiment, mortality of female grasshoppers ovipositing into a sterile loamy-sand soil containing conidia of B. bassiana was measured. The prevalence of mortality increased as the concentration of conidia in soil increased, and a median lethal concentration of 10(4) colony-forming units (CFU) per gram of soil (dry weight) was observed. Conidia (10(2.9) to 10(3) CFU per abdomen) were recovered from the abdomens of grasshoppers ovipositing into sand containing 10(5.5) and 10(6) conidia per gram. Similar numbers of eggs were laid among treatments during the first oviposition period (1 to 7 days), but an effect of conidial concentration on eggs laid was observed during the second oviposition period (8 to 14 days). This was attributed to reduction in female numbers and not to reduction in fecundity independent of mortality. In a second experiment, grasshoppers oviposited into soils of three different textures (loamy-sand, sandy-loam, or clay-loam) that were amended with 10(5) B. bassiana conidia per gram and possessed either a viable or heat-killed microflora. There was no effect of soil texture on mortality of ovipositing grasshoppers, on the number of eggs laid, on positioning of egg pods in the soil profile, or on numbers of B. bassiana CFU recovered from female abdomens. However, a higher prevalence of mortality was observed for females ovipositing into the sterilized than nonsterilized sandy-loam and clay-loam soils. Substantial populations of fungi and bacteria were recovered from nonsterilized soils. The predominant fungi isolated from these soils were members of the genera Chrysosporium, Fusarium, Gliocladium, Penicillium, Rhizopus, and Trichoderma, whereas Bacillus, Paenibacillus, and Pseudomonas species were the most commonly isolated bacteria. This study demonstrates that ovipositing grasshoppers are susceptible to relatively low densities of conidia in soils of varying textures, but the soil microflora may have an adverse affect on the efficacy of B. bassiana in field soils. Copyright 1998 Academic Press. Copyright 1998 Academic Press

Journal Article↗
PubMed1999

The establishment of an introduced community of fluorescent pseudomonads in the soil and in the rhizosphere is affected by the soil type.

Indigenous populations of fluorescent pseudomonads were previously shown to vary in two different soils (Châteaurenard and Dijon) and in the rhizosphere of a plant species (Linum usitatissimum L.) cultivated in these two soils. These differences could be related to the soil type and to their crop history. In the present study, the influence of the soil type on the diversity of fluorescent pseudomonads in bulk and rhizospheric soils was evaluated. The soils of Châteaurenard and Dijon were sterilized before being inoculated with the same community of fluorescent pseudomonads. Bacterial isolates from bulk and rhizospheric soils were characterized on the basis of their repetitive extragenic palindromic-PCR patterns allowing the comparison of the distributions of the introduced populations. The influence of the soil type on the establishment of the introduced bacterial community was recorded in the two bulk soils. Indeed, the density and the structure of the community differed significantly between the two soils. The rhizosphere effect was also affected by the soil type. This effect was expressed in the Châteaurenard soil but not in the Dijon soil. Hence, the structure of the bacterial community associated with the roots of the same plant species cultivated in the two soils differed significantly.

Journal Article↗