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Modeling phosphorus concentrations in Irish rivers using land use, soil type, and soil phosphorus data.

Modeling diffuse phosphorus (P) loss may indicate management strategies to minimize P loss from agricultural sources. An empirical model predicting flow-weighted phosphorus concentrations (MRP) was derived using data collected from 35 Irish river catchments. Monitoring records of riverine P and stream flow data were used to calculate MRP values averaged for the years 1991-1994. These data were modeled using land use, soil type, and soil P data. Soil type in catchments was described using soil survey classifications weighted according to their P desorption properties from laboratory results. Soil test P concentrations for the studied watersheds were obtained from a national database. Soil P levels were weighted based on the results of field experiments measuring P losses in overland flow from fields at different soil test P levels. The 35 catchments were statistically clustered into two populations (A and B) based on differences in soil type, specifically, soil hydrology. Catchments in Cluster A had predominantly poorly drained soils and comparatively higher MRP concentrations (0.03-0.17 mg L(-1)) than Cluster B areas (0.01-0.7 mg L(-1)) with mostly well-drained soils. Regression equations derived for A and B type catchments predicted MRP values with 68 and 62% of the variation explained in the models, respectively. Data extracted for the rest of the country were applied to the models to delineate areas at risk on a national scale. While the models were only moderately accurate they highlighted the influence of land management, specifically, high production grassland receiving high P inputs, in conjunction with the effect of soil type and soil hydrology on the transport of P to surface waters.

Agriculture↗

PubMed2004

Development and survival of Anopheles gambiae eggs in drying soil: influence of the rate of drying, egg age, and soil type.

Little is known about the contribution made by the egg stage of African malaria vectors to the rapid rise in adult populations following the onset of seasonal rains. To examine this issue, we evaluated the viability of Anopheles gambiae eggs in drying soil in the laboratory. Survival data were collected from field-caught mosquitoes kept in sandy loam soil and laboratory-reared colonies kept in sandy loam soil and black cotton soil. Under high, medium, and low soil-moisture regimes, egg viability declined sharply with increased duration of drying. Eggs remained viable in drying sandy loam soil for 1, 5, and 10 days, but not after 15 or 20 days. The most dramatic decline in hatching success occurred between drying days 1 (78-83% hatch) and 5 (20-23% hatch). In contrast, eggs reared in high-moisture black cotton soil remained viable for up to 15 days. Furthermore, after 5 drying days, high-, medium-, and low-moisture soils averaged 59, 47, and 31% hatching success, respectively. We recovered unhatched eggs from sandy loam soils to examine the developmental status of the embryos. A majority of the unhatched eggs that were recovered from days 15 and 20 in sandy loam soils contained fully developed late-stage embryos. Thus, unhatched eggs completed embryonic development but probably died before receiving an appropriate hatching stimulus. Our results suggest that the absolute moisture content of the soil does not alone determine hatching success of anopheline eggs. Rather, soil moisture, together with the rate of drying, physiological factors associated with the age of the egg, and the type of soil in which the egg rests likely influence survival.

Animals↗

PubMed2005

Intrinsic and induced isoproturon catabolic activity in dissimilar soils and soils under dissimilar land use.

The catabolic activity with respect to the systemic herbicide isoproturon was determined in soil samples by (14)C-radiorespirometry. The first experiment assessed levels of intrinsic catabolic activity in soil samples that represented three dissimilar soil series under arable cultivation. Results showed average extents of isoproturon mineralisation (after 240 h assay time) in the three soil series to be low. A second experiment assessed the impact of addition of isoproturon (0.05 microg kg(-1)) into these soils on the levels of catabolic activity following 28 days of incubation. Increased catabolic activity was observed in all three soils. A third experiment assessed levels of intrinsic catabolic activity in soil samples representing a single soil series managed under either conventional agricultural practice (including the use of isoproturon) or organic farming practice (with no use of isoproturon). Results showed higher (and more consistent) levels of isoproturon mineralisation in the soil samples collected from conventional land use. The final experiment assessed the impact of isoproturon addition on the levels of inducible catabolic activity in these soils. The results showed no significant difference in the case of the conventional farm soil samples while the induction of catabolic activity in the organic farm soil samples was significant.

Agriculture↗

PubMed2006

Comparing contributions of soil versus root colonization to variations in stomatal behavior and soil drying in mycorrhizal Sorghum bicolor and Cucurbita pepo.

In prior studies we learned that colonization of soil can be as important as colonization of roots in determining mycorrhizal influence on the water relations of host plants. Here we use a path analysis modeling approach to test (a) whether quantity of hyphae in soil contributes to variations in stomatal behavior and soil drying, and (b) whether soil colonization or root colonization has a stronger influence on these stomatal and soil drying responses. Experiments were performed on Sorghum bicolor and Cucurbita pepo, with soils and roots colonized by a mixture of Glomus intraradices and Gigaspora margarita. Soil colonization generally made more significant contributions to stomatal conductance than did root colonization. Soil colonization did not make significant direct contributions to soil water potential measures (soil water potential at stomatal closure or soil drying rate), whereas root colonization did contribute a potentially important path to each. The findings further support a role for mycorrhization of the soil itself in contributing to the regulation of stomatal behavior of host plants.

Cucurbita↗

PubMed2002

Horizontal and vertical movement of Pseudomonas fluorescens toward exudate of Macrophomina phaseolina in soil: influence of motility and soil properties.

The role of motility and cell surface hydrophobicity in transport and dispersal of Pseudomonas fluorescens strains LAM1-hydrophilic, LAM2-hydrophobic and LAM(NM) (non-motile mutant of LAM2) under different soil conditions was studied. Maximum adhesion was recorded for LAM2 in clay loam (70%), followed by sandy loam (68%) and sandy soil (40%). Vertical migration of P fluorescens isolates in soils was recorded at 5 and 25 cm flow of wafer or M. phaseolina exudate. In all the treatments, LAM1 exhibited maximum migration followed, by LAM2 and LAM(NM). The rate of migration of such isolates was lowered in water irrigated soils compared to those irrigated with M. phaseolina exudate. In sandy soil, cells of LAM1 migrated up to 13 cm in comparison to LAM2 (11 cm) and LAN(NM) (9 cm) at 5 cm flow of fungal exudate. Population of LAM1, LAM2 and LAM(NM) was 5.7, 5.68 and 5.61 log cfu g(-1) soil at 1 cm depth, but it decreased to 2.56, 2.21 and 1.99 log cfu during migration up to 11 cm in sandy soil at 5 cm flow of fungal exudate. Greater motility was observed in sandy soil irrigated with water or fungal exudate, followed by sandy loam and clay loam. In general, filtration coefficient (lambda) of P. fluorescens was higher in soils irrigated with 5 cm of water or exudate than with 25 cm of irrigation. The horizontal movement of P. fluorescens strains in sandy soil adjusted at different psi m showed marked reduction with decrease in psi m. The non-motile LAN(NM) did not show chemotactic response and migrated up to a maximum of 3 mm in saturated soils (0 kPa). After 96 h, LAM1 and LAM2 migrated upto 35 and 29 mm respectively in sandy soil. Motile isolates had significantly greater colonization of M. phaseolina sclerotia over the non-motile mutant.

Aluminum Silicates↗

PubMed2003

Selenium and sulfur accumulation and soil selenium dissipation in planting of four herbaceous plant species in soil contaminated with drainage sediment rich in both selenium and sulfur.

Four selenium (Se) nonaccumulator plant species, including a forage grass species, Tall Fescue (Festuca arundinacea Schreb.), a forage legume species, Alfalfa (Medicago sativa L.), a wetland species, Rush (Juncus tenuis Wild.), and a dry-land alkaline soil species, Saltgrass (Distichlis spicata L.), were grown in soil contaminated by agricultural drainage sediment having elevated levels of Se and sulfur (S). The above-ground plant tissues were consecutively harvested five times and examined for Se and S accumulation. Plant tissue Se concentrations ranged from 23.0 mg kg-1 to 8.3 mg kg-1. Tissue S concentrations ranged from 3239 mg kg-1 to 7034 mg kg-1. Both tissue Se and S concentrations were significantly different between harvests, species, and species/harvest interactions. Total Se accumulation by the plant biomass harvested ranged from 0.3 to 1.3 mg per soil column and total S accumulations ranged from 87.5 to 321.1 mg per soil column. The reduction in the percentage of total soil Se after 24 weeks growth of the plant species ranged from 12.0% in the Tall Fescue planting to 17.3% in the Rush planting. Over 90% of the soil Se losses were unidentified losses and leaching of Se was prevented. The accumulations of Se and S in the plant biomass were very small compared with the total soil Se and S losses, but substantial amounts of total soil Se (12.0 to 15.0%) and S (28.0 to 50.9%) inventories were dissipated by the growing and harvesting of the plants. The soil S concentration was several hundred times higher than the soil Se concentration, but Se accumulation by the plants and Se dissipation from the soil were not impaired by the high level of soil sulfur. For natural grassland habitat restoration, such as at the Kesterson Wildlife Refuge in the Central Valley of California, or for restoration of large-scale Se contaminated agricultural lands, Se nonaccumulator plant species are favorable candidates, because the possibility of introducing Se toxicity into the food chain can be minimized.

Biodegradation, Environmental↗

PubMed2001

Comparison of nifH gene pools in soils and soil microenvironments with contrasting properties.

The similarities and differences in the structures of the nifH gene pools of six different soils (Montrond, LCSA-p, Vernon, Dombes, LCSA-c, and Thysse Kaymor) and five soil fractions extracted from LCSA-c were studied. Bacterial DNA was directly extracted from the soils, and a region of the nifH gene was amplified by PCR and analyzed by restriction. Soils were selected on the basis of differences in soil management, plant cover, and major physicochemical properties. Microenvironments differed on the basis of the sizes of the constituent particles and the organic carbon and clay contents. Restriction profiles were subjected to principal-component analysis. We showed that the composition of the diazotrophic communities varied both on a large scale (among soils) and on a microscale (among microenvironments in LCSA-c soil). Soil management seemed to be the major parameter influencing differences in the nifH gene pool structure among soils by controlling inorganic nitrogen content and its variation. However, physicochemical parameters (texture and total C and N contents) were found to correlate with differences among nifH gene pools on a microscale. We hypothesize that the observed nifH genetic structures resulted from the adaptation to fluctuating conditions (cultivated soil, forest soil, coarse fractions) or constant conditions (permanent pasture soil, fine fractions). We attempted to identify a specific band within the profile of the clay fraction by cloning and sequencing it and comparing it with the gene databases. Unexpectedly, the nifH sequences of the dominant bacteria were most similar to sequences of unidentified marine eubacteria.

Bacteria↗

PubMed2003

Respiration of 13C-labeled substrates added to soil in the field and subsequent 16S rRNA gene analysis of 13C-labeled soil DNA.

Our goal was to develop a field soil biodegradation assay using (13)C-labeled compounds and identify the active microorganisms by analyzing 16S rRNA genes in soil-derived (13)C-labeled DNA. Our biodegradation approach sought to minimize microbiological artifacts caused by physical and/or nutritional disturbance of soil associated with sampling and laboratory incubation. The new field-based assay involved the release of (13)C-labeled compounds (glucose, phenol, caffeine, and naphthalene) to soil plots, installation of open-bottom glass chambers that covered the soil, and analysis of samples of headspace gases for (13)CO(2) respiration by gas chromatography/mass spectrometry (GC/MS). We verified that the GC/MS procedure was capable of assessing respiration of the four substrates added (50 ppm) to 5 g of soil in sealed laboratory incubations. Next, we determined background levels of (13)CO(2) emitted from naturally occurring soil organic matter to chambers inserted into our field soil test plots. We found that the conservative tracer, SF(6), that was injected into the headspace rapidly diffused out of the soil chamber and thus would be of little value for computing the efficiency of retaining respired (13)CO(2). Field respiration assays using all four compounds were completed. Background respiration from soil organic matter interfered with the documentation of in situ respiration of the slowly metabolized (caffeine) and sparingly soluble (naphthalene) compounds. Nonetheless, transient peaks of (13)CO(2) released in excess of background were found in glucose- and phenol-treated soil within 8 h. Cesium-chloride separation of (13)C-labeled soil DNA was followed by PCR amplification and sequencing of 16S rRNA genes from microbial populations involved with (13)C-substrate metabolism. A total of 29 full sequences revealed that active populations included relatives of Arthrobacter, Pseudomonas, Acinetobacter, Massilia, Flavobacterium, and Pedobacter spp. for glucose; Pseudomonas, Pantoea, Acinetobacter, Enterobacter, Stenotrophomonas, and Alcaligenes spp. for phenol; Pseudomonas, Acinetobacter, and Variovorax spp. for naphthalene; and Acinetobacter, Enterobacter, Stenotrophomonas, and Pantoea spp. for caffeine.

Bacteria↗

PubMed1975

Soil fungistasis: elevation of the exogenous carbon and nitrogen requirements for spore germination by fungistatic volatiles in soils.

Axenic, washed conidia of Fusarium solani f. sp. phaseoli, Aspergillus flavus, and Verticillium albo-atrum were placed on washed Difco purified agar discs along with an inorganic salt solution containing various levels of carbon and nitrogen substrates. These discs were exposed to volatiles from six soils (pH 5.1-8.6). Fusarium solani macroconidial germination was inhibited mostly by volatiles from soils of pH 5.1, 6.1, 7.0, and 7.5, but high levels of glucose and NH4Cl reversed this inhibition, raising germination to that of no-soil, no-carbon or nitrogen controls. Conidial germination of A. flavus was inhibited mainly by volatiles from high pH (7.0, 7.8, and 8.6) soils, and increased levels of glucose plus an amino acid mixture nullified this inhibition. Volatiles from soils of pH 5.1, 6.1, and 7.5 stimulated A. flavus conidial germination. Assays after the removal of CO2 from the air above soil of pH 5.1 demonstrated that volatiles inhibitory to A. flavus were produced by this soil. Assays indicated that a KOH-soluble compound was a fungistatic soil volatile to F. solani macroconidial germination. The nullification by carbon and nitrogen substrates of F. solani and A. flavus inhibition caused by soil volatiles parallels that for soil fungistasis. Conidial germination of V. albo-atrum was markedly stimulated by volatiles in all soils tested, and was not affected by removal of CO2. Inhibitory soil volatiles may increase the nutritional requirements for spore germination of certain fungi.

Amino Acids↗

PubMed2006

[Relationships between soil microbial ecological characteristics and physical-chemical properties of vegetable garden soil].

The study on the 64 vegetable garden soil samples in the Baiyuan District of Guangzhou City showed that there were significantly positive correlations of soil microbial biomass carbon (Cmic) with soil total N, alkali-hydrolygable N, available K, cation exchange capacity (CEC) and organic matter (OM), of soil microbial biomass nitrogen (Nmic) with soil total N, total P, CEC and OM, of soil basal respiration (SBR) with soil total N, alkali-hydrolygable N, available K, CEC and OM, of AWCD with soil total N and OM, and of Shannon diversity index with soil total N and CEC. Low alkali-hydrolygable N increased Cmic SBR, and metabolic quotient (qCO2), while high alkali-hydrolygable N decreased qCO2. High available P decreased Cmic, Nmic and microbial quotient, and a high ratio of available P to alkali-hydrolygable N was related to the decrease of Cmic, Nmic, Cmic/Nmic and SBR. It was suggested that there were significant correlations between soil microbial ecological characteristics and physico-chemical properties, and excessive available nutrients or inappropriate ratios of alkali-hydrolygable N to available P in soil were harmful to soil microbes.

Carbon↗

PubMed2004