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Agricultural Fields (agricultural + field)
Selected AbstractsEFFECTS OF TOPOGRAPHY AND SOIL PROPERTIES ON RECHARGE AT TWO SITES IN AN AGRICULTURAL FIELD,JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, Issue 6 2000Geoffrey N. Delin ABSTRACT: Field experiments were conducted from 1992 to 1995 to estimate ground water recharge rates at two sites located within a 2.7-hectare agricultural field. The field lies in a sand plain setting in central Minnesota and is cropped continuously in field corn. The sites are located at a topographically high (upland) site and a topographically low (lowland) site in an effort to quantify the effects of depression focusing of recharge. Three site-specific methods were used to estimate recharge rates: well hydrograph analysis, chlorofluorocarbon age dating, and an unsaturated zone water balance. All three recharge methods indicated that recharge rates at the lowland site (annual average of all methods of 29 cm) exceeded those at the upland site (annual average of 18 cm). On an annual basis, estimates by the individual methods ranged from 12 to 44 percent of precipitation at the upland site and from 21 to 83 percent at the lowland site. The difference in recharge rates between the sites is primarily attributed to depression focusing of surface water runon at the lowland site. However, two other factors were also important: the presence of thin lamellae at the upland site, and coarser textured soils below a depth of 1.5 m at the lowland site. [source] Activated Carbon as a Restoration Tool: Potential for Control of Invasive Plants in Abandoned Agricultural FieldsRESTORATION ECOLOGY, Issue 2 2006Andrew Kulmatiski Abstract Exotic plants have been found to use allelochemicals, positive plant,soil feedbacks, and high concentrations of soil nutrients to exercise a competitive advantage over native plants. Under laboratory conditions, activated carbon (AC) has shown the potential to reduce these advantages by sequestering organic compounds. It is not known, however, if AC can effectively sequester organics or reduce exotic plant growth under field conditions. On soils dominated by exotic plants, we found that AC additions (1% AC by mass in the top 10 cm of soil) reduced concentrations of extractable organic C and N and induced consistent changes in plant community composition. The cover of two dominant exotics, Bromus tectorum and Centaurea diffusa, decreased on AC plots compared to that on control plots (14,8% and 4,0.1%, respectively), and the cover of native perennial grasses increased on AC plots compared to that on control plots (1.4,3% cover). Despite promising responses to AC by these species, some exotic species responded positively to AC and some native species responded negatively to AC. Consequently, AC addition did not result in native plant communities similar to uninvaded sites, but AC did demonstrate potential as a soil-based exotic plant control tool, especially for B. tectorum and C. diffusa. [source] In situ measurement of methane fluxes and analysis of transcribed particulate methane monooxygenase in desert soilsENVIRONMENTAL MICROBIOLOGY, Issue 10 2009Roey Angel Summary Aerated soils are a biological sink for atmospheric methane. However, the activity of desert soils and the presence of methanotrophs in these soils have hardly been studied. We studied on-site atmospheric methane consumption rates as well as the diversity and expression of the pmoA gene, coding for a subunit of the particulate methane monooxygenase, in arid and hyperarid soils in the Negev Desert, Israel. Methane uptake was only detected in undisturbed soils in the arid region (,90 mm year,1) and vertical methane profiles in soil showed the active layer to be at 0,20 cm depth. No methane uptake was detected in the hyperarid soils (,20 mm year,1) as well as in disturbed soils in the arid region (i.e. agricultural field and a mini-catchment). Molecular analysis of the methanotrophic community using terminal restriction fragment length polymorphism (T-RFLP) and cloning/sequencing of the pmoA gene detected methanotrophs in the active soils, whereas the inactive ones were dominated by sequences of the homologous gene amoA, coding for a subunit of the ammonia monooxygenase. Even in the active soils, methanotrophs (as well as in situ activity) could not be detected in the soil crust, which is the biologically most important layer in desert soils. All pmoA sequences belonged to yet uncultured strains. Transcript analysis showed dominance of sequences clustering within the JR3, formerly identified in Californian grassland soils. Our results show that although active methanotrophs are prevalent in arid soils they seem to be absent or inactive in hyperarid and disturbed arid soils. Furthermore, we postulate that methanotrophs of the yet uncultured JR3 cluster are the dominant atmospheric methane oxidizers in this ecosystem. [source] Factors controlling aggregation in a minimum and a conventionally tilled undulating fieldEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 5 2007S. De Gryze Summary Wind and water erosion induce breakdown of soil aggregates and loss of soil organic matter. Whereas most of the relations between aggregation and its driving factors have been established on a plot scale, these relations might be very different within an undulating landscape where both erosion (by wind or water) and deposition occur. The aim of this study was to investigate to what degree spatial patterns in soil variables influence spatial patterns in aggregation under different tillage intensities. We studied an agricultural field of about 3 ha in the silty region of Belgium. The site was split into a conventional tillage (CT) and a minimum tillage (MT) system. Within the field, 396 geo-referenced surface soil samples (0,5 cm) were taken and analyzed for organic matter content, quantity of aggregates and a number of other soil properties. Under CT, 28.5% of the total sample variation was explained by the occurrence of depositional areas, 20.8% by the amount of soil organic matter, and 13.8% by the presence of a clay-rich B horizon which surfaced due to progressive water and tillage erosion. Regression analysis revealed that 27% of the variation in the quantity of macroaggregates (>0.25 mm) was accounted for by these three factors. Under MT, 27.1% of the total sample variation was related to the surface cover of Tertiary sand, 22.6% to the amount of soil organic matter, and 13% to erodibility. These three factors explained 53% of the variation in the quantity of macroaggregates. In the CT system, the correlation between grass- or maize- carbon and the quantity of macroaggregates was strongly linked to erodibility, while this was not the case in the MT system. We concluded that at this site, macroaggregation is dominated by landscape-scale processes (such as water or tillage erosion) rather than determined by the commonly considered local variables (such as small variations in texture or organic matter content). [source] Lignin turnover in an agricultural field: from plant residues to soil-protected fractionsEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 4 2006D. P. Rasse Summary Lignin has long been suspected to be a major source of stable carbon in soils, notably because of the recalcitrant nature of its polyphenolic structure relative to other families of plant molecules. However, lignin turnover studies have produced conflicting results, most of them suggesting that large proportions of plant-residue lignin decompose within a year of incorporation into soils. Here, we propose a two-reservoir model where lignin in undecomposed plant residue (Lp) can either reach soil fractions where it is somewhat protected from further decomposition (Ls) or is transformed to non-lignin products. Model calibration data were obtained through compound-specific 13C isotopic analyses conducted in a zero- to 9-year chronosequence of maize monoculture after wheat in a temperate loam soil of the Paris basin. Lignin was quantified by CuO oxidation as VSC-lignin, i.e. the sum of vanillil- (V), syringyl- (S) and coumaryl-type (C) phenols. Model calibrations indicate that Lp has a turnover rate faster than 1 year and that 92% is mineralized as CO2 or transformed into other non-lignin products, while only 8% reaches the Ls fraction. Estimated turnover rate of the Ls fraction was 0.05 years,1. The model also suggested that about half of Lp was not measured because it had been excluded from the samples in the process of sieving at 5 mm. In conclusion, the model indicates that chemical recalcitrance alone is not sufficient to explain VSC-lignin turnover in soils, and that, functionally, the most relevant mechanism appears to be the transfer of VSC-lignin molecules and fragments from decomposing plant tissues to soil-protected fractions. [source] Microbial degradation of isoproturon and related phenylurea herbicides in and below agricultural fieldsFEMS MICROBIOLOGY ECOLOGY, Issue 1 2003Sebastian R Sørensen Abstract The phenylurea herbicides are an important group of pesticides used extensively for pre- or post-emergence weed control in cotton, fruit and cereal crops worldwide. The detection of phenylurea herbicides and their metabolites in surface and ground waters has raised the awareness of the important role played by agricultural soils in determining water quality. The degradation of phenylurea herbicides following application to agricultural fields is predominantly microbial. However, evidence suggests a slow degradation of the phenyl ring, and substantial spatial heterogeneity in the distribution of active degradative populations, which is a key factor determining patterns of leaching losses from agricultural fields. This review summarises current knowledge on the microbial metabolism of isoproturon and related phenylurea herbicides in and below agricultural soils. It addresses topics such as microbial degradation of phenylurea herbicides in soil and subsurface environments, characteristics of known phenylurea-degrading soil micro-organisms, and similarities between metabolic pathways for different phenylurea herbicides. Finally, recent studies in which molecular and microbiological techniques have been used to provide insight into the in situ microbial metabolism of isoproturon within an agricultural field will be discussed. [source] Plant diversity positively affects short-term soil carbon storage in experimental grasslandsGLOBAL CHANGE BIOLOGY, Issue 12 2008SIBYLLE STEINBEISS Abstract Increasing atmospheric CO2 concentration and related climate change have stimulated much interest in the potential of soils to sequester carbon. In ,The Jena Experiment', a managed grassland experiment on a former agricultural field, we investigated the link between plant diversity and soil carbon storage. The biodiversity gradient ranged from one to 60 species belonging to four functional groups. Stratified soil samples were taken to 30 cm depth from 86 plots in 2002, 2004 and 2006, and organic carbon contents were determined. Soil organic carbon stocks in 0,30 cm decreased from 7.3 kg C m,2 in 2002 to 6.9 kg C m,2 in 2004, but had recovered to 7.8 kg C m,2 by 2006. During the first 2 years, carbon storage was limited to the top 5 cm of soil while below 10 cm depth, carbon was lost probably as short-term effect of the land use change. After 4 years, carbon stocks significantly increased within the top 20 cm. More importantly, carbon storage significantly increased with sown species richness (log-transformed) in all depth segments and even carbon losses were significantly smaller with higher species richness. Although increasing species diversity increased root biomass production, statistical analyses revealed that species diversity per se was more important than biomass production for changes in soil carbon. Below 20 cm depth, the presence of one functional group, tall herbs, significantly reduced carbon losses in the beginning of the experiment. Our analysis indicates that plant species richness and certain plant functional traits accelerate the build-up of new carbon pools within 4 years. Additionally, higher plant diversity mitigated soil carbon losses in deeper horizons. This suggests that higher biodiversity might lead to higher soil carbon sequestration in the long-term and therefore the conservation of biodiversity might play a role in greenhouse gas mitigation. [source] Prediction of concentrated flow width in ephemeral gully channelsHYDROLOGICAL PROCESSES, Issue 10 2002J. Nachtergaele Abstract Empirical prediction equations of the form W = aQb have been reported for rills and rivers, but not for ephemeral gullies. In this study six experimental data sets are used to establish a relationship between channel width (W, m) and flow discharge (Q, m3 s,1) for ephemeral gullies formed on cropland. The resulting regression equation (W = 2·51 Q0·412; R2 = 0·72; n = 67) predicts observed channel width reasonably well. Owing to logistic limitations related to the respective experimental set ups, only relatively small runoff discharges (i.e. Q < 0·02 m3s,1) were covered. Using field data, where measured ephemeral gully channel width was attributed to a calculated peak runoff discharge on sealed cropland, the application field of the regression equation was extended towards larger discharges (i.e. 5 × 10,4m3s,1 < Q < 0·1 m3s,1). Comparing W,Q relationships for concentrated flow channels revealed that the discharge exponent (b) varies from 0·3 for rills over 0·4 for gullies to 0·5 for rivers. This shift in b may be the result of: (i) differences in flow shear stress distribution over the wetted perimeter between rills, gullies and rivers, (ii) a decrease in probability of a channel formed in soil material with uniform erosion resistance from rills over gullies to rivers and (iii) a decrease in average surface slope from rills over gullies to rivers. The proposed W,Q equation for ephemeral gullies is valid for (sealed) cropland with no significant change in erosion resistance with depth. Two examples illustrate limitations of the W,Q approach. In a first example, vertical erosion is hindered by a frozen subsoil. The second example relates to a typical summer situation where the soil moisture profile of an agricultural field makes the top 0·02 m five times more erodible than the underlying soil material. For both cases observed W values are larger than those predicted by the established channel width equation for concentrated flow on cropland. For the frozen soils the equation W = 3·17 Q0·368 (R2 = 0·78; n = 617) was established, but for the summer soils no equation could be established. Copyright © 2002 John Wiley & Sons, Ltd. [source] EVALUATION OF COASTAL PLAIN CONSERVATION BUFFERS USING THE RIPARIAN ECOSYSTEM MANAGEMENT MODEL,JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, Issue 6 2001Richard Lowrance ABSTRACT: Riparian buffers are increasingly important as watershed management tools and are cost-shared by programs such as Conservation Reserve that are part of the USDA Conservation Buffer Initiative. Riparian buffers as narrow as 4.6m (15ft) are eligible for cost-share by USDA. The Riparian Ecosystem Management Model (REMM) provides a tool to judge water quality improvement by buffers and to set design criteria for nutrient and sediment load reduction. REMM was used for a Coastal Plain site to simulate 14 different buffers ranging from 4.6 m to 51.8 m (15 to 170 ft) with three different types of vegetation (hardwood trees, pine trees, and perennial grass) with two water and nutrient loads. The load cases were low sediment/low nutrient-typical of a well managed agricultural field and low sediment/high nutrient-typical of liquid manure application to perennial forage crops. Simulations showed that the minimum width buffer (4.6 m) was inadequate for control of nutrients under either load case. The minimum width buffer that is eligible for cost share assistance on a field with known water quality problems (10.7 m, 35 ft) was projected to achieve at least 50 percent reduction of N, P, and sediment in the load cases simulated. [source] EFFECTS OF TOPOGRAPHY AND SOIL PROPERTIES ON RECHARGE AT TWO SITES IN AN AGRICULTURAL FIELD,JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, Issue 6 2000Geoffrey N. Delin ABSTRACT: Field experiments were conducted from 1992 to 1995 to estimate ground water recharge rates at two sites located within a 2.7-hectare agricultural field. The field lies in a sand plain setting in central Minnesota and is cropped continuously in field corn. The sites are located at a topographically high (upland) site and a topographically low (lowland) site in an effort to quantify the effects of depression focusing of recharge. Three site-specific methods were used to estimate recharge rates: well hydrograph analysis, chlorofluorocarbon age dating, and an unsaturated zone water balance. All three recharge methods indicated that recharge rates at the lowland site (annual average of all methods of 29 cm) exceeded those at the upland site (annual average of 18 cm). On an annual basis, estimates by the individual methods ranged from 12 to 44 percent of precipitation at the upland site and from 21 to 83 percent at the lowland site. The difference in recharge rates between the sites is primarily attributed to depression focusing of surface water runon at the lowland site. However, two other factors were also important: the presence of thin lamellae at the upland site, and coarser textured soils below a depth of 1.5 m at the lowland site. [source] Evaluation of statistical protocols for quality control of ecosystem carbon dioxide fluxesJOURNAL OF THE ROYAL STATISTICAL SOCIETY: SERIES A (STATISTICS IN SOCIETY), Issue 1 2007Jorge F. Perez-Quezada Summary., The process of quality control of micrometeorological and carbon dioxide (CO2) flux data can be subjective and may lack repeatability, which would undermine the results of many studies. Multivariate statistical methods and time series analysis were used together and independently to detect and replace outliers in CO2 flux data derived from a Bowen ratio energy balance system. The results were compared with those produced by five experts who applied the current and potentially subjective protocol. All protocols were tested on the same set of three 5-day periods, when measurements were conducted in an abandoned agricultural field. The concordance of the protocols was evaluated by using the experts' opinion (mean ± 1.96 standard deviations) as a reference interval (the Bland,Altman method). Analysing the 15 days together, the statistical protocol that combined multivariate distance, multiple linear regression and time series analysis showed a concordance of 93% on a 20-min flux basis and 87% on a daily basis (only 2 days fell outside the reference interval), and the overall flux differed only by 1.7% (3.2 g CO2 m,2). An automated version of this or a similar statistical protocol could be used as a standard way of filling gaps and processing data from Bowen ratio energy balance and other techniques (e.g. eddy covariance). This would enforce objectivity in comparisons of CO2 flux data that are generated by different research groups and streamline the protocols for quality control. [source] Bacterial diversity in maize rhizospheres: conclusions on the use of genetic profiles based on PCR-amplified partial small subunit rRNA genes in ecological studiesMOLECULAR ECOLOGY, Issue 1 2003Achim Schmalenberger Abstract A cultivation-independent approach based on polymerase chain reaction (PCR)-amplified partial small subunit rRNA genes and genetic profiling by single-strand conformation polymorphism (SSCP) was used to characterize the bacterial diversity inhabiting the rhizosphere of maize plants grown on an agricultural field. The community structures of two cultivars, a genetically engineered and a nonengineered variety, different herbicide regimes and soil tillage were compared with each other at two sampling dates. SSCP-profiles were generated with DNA from bacterial cell consortia with primers hybridizing to evolutionarily highly conserved rRNA gene regions. On silver-stained gels, each profile consisted of approx. 50 distinguishable bands. Similarity analyses of patterns recorded by digital image analyses could not detect any difference between cultivars or treatments that was greater than the variability between replicates. A total of 54 sequences recovered from different bands were identified and grouped into operational taxonomical units (OTUs). Surprisingly, only five of 40 OTUs contained sequences of both samplings. Three different bands from a profile were selected to test whether this small overlap was due to an incomplete recovery of sequences. From a faint band, two different OTUs were found when 12 clones were analysed, and from two strong bands 24 and 22 OTUs were detected from a total of 26 and 36 clones, respectively. The OTUs belonged to phylogenetically different groups of bacteria. Gene probes that were developed to target different bands of the profiles, however, indicated in Southern blot analyses that patterns between treatments, replicates and samplings, and even from two different growing seasons were highly conserved. Our study demonstrates that community profiles can consist of more sequences than detectable by staining and that gene probes in Southern blot can be a useful control to investigate the composition of microbial communities by genetic profiles. [source] Spatial variability in the mineralisation of the phenylurea herbicide linuron within a Danish agricultural field: multivariate correlation to simple soil parameters,PEST MANAGEMENT SCIENCE (FORMERLY: PESTICIDE SCIENCE), Issue 9 2005Jim Rasmussen Abstract The spatial variability in the mineralisation rate of linuron [N -(3,4-dichlorophenyl)- N,-methoxy- N,-methylurea] was studied within a previously treated Danish agricultural field by sampling soils from eleven different plots randomly distributed across an area of 20 × 20 m. The soils were characterised with respect to different abiotic and biotic properties including moisture content, organic matter content, pH, nutrient content, bacterial biomass, potential for mineralisation of MCPA [(4-chloro-2-methylphenoxy)acetic acid] and linuron. Five soils had a potential for mineralisation of linuron, with 5,15% of the added [ring -U- 14C]linuron metabolised to 14CO2 within 60 days at 10 °C, while no extensive mineralisation of linuron was observed in the six remaining soils within this period. A TLC analysis of the methanol-extractable residues showed no development of 14C-labelled metabolites from linuron in any of the samples. Multivariate analysis was conducted to elucidate relationships between the intrinsic properties of single soil samples and initial rate of linuron mineralisation. The analysis indicated that important soil parameters in determining the spatial heterogeneity included the Ctotal/Ntotal ratio, pH and the water-extractable potassium contents, with the first of these highly negatively correlated and the last two highly positively correlated to the initial linuron mineralisation rate. This study shows that enhanced biodegradation of linuron may develop with successive field treatments, but that considerable in-field spatial heterogeneity in the degradation rate still exists. Combined with a parallel enrichment study focused on the underlying microbial processes, the present results suggest that intrinsic soil properties affect the linuron-metabolising bacterial population and thereby determine the spatial variability in the linuron mineralisation activity. Copyright © 2005 Society of Chemical Industry [source] Vegetative Characteristics of Recently Reforested Bottomlands in the Lower Cache River Watershed, Illinois, U.S.A.RESTORATION ECOLOGY, Issue 3 2003Brian S. Kruse Abstract Interest in restoring native ecosystems is resulting in conversion of marginal agricultural lands to bottomland hardwood-dominated forests in the midwestern and midsouthern United States. Growing stock for these efforts typically consists of planted oak (Quercus spp.) and volunteer vegetation. Reports of mixed reforestation success and the lack of post-establishment tree growth data prompted this evaluation of vegetation characteristics of 5- to 7-year-old operational restorations in the Lower Cache River Watershed in southernmost Illinois, U.S.A. Fraxinus pennsylvanica (green ash), Acer negundo (box-elder), and Liquidambar styraciflua (sweetgum) together comprised 77% of all tree stems observed. Full stocking of overstory tree species can be expected to produce a closed canopy stand within 160 m of a forested edge, due primarily to the abundance of rapidly growing volunteer-origin trees. Planted oaks contributed minimally to total tree stocking but were present in sufficient numbers to eventually improve wildlife habitat, and therefore satisfied restoration objectives. Oak height was 23% greater when in the presence of a non-oak tree species. Herbaceous cover was dominated by Solidago gigantea (late goldenrod) and Juncus spp. (rushes). Solidago gigantea was associated with poor growth and low density of non-oak stems, whereas Juncus dudleyi (Dudley's rush) was associated with taller non-oak stems. These results suggest that the presence of volunteer-origin trees is crucial for the creation of full stand stocking that will result in rapid development of a closed canopy forest. Improved success of future reforestation efforts will require more intensive methods to establish adequate stocking beyond 160 m of a forest edge. Methods described here could be adapted for agricultural field to forest restorations in other regions to predict critical distances from volunteer seed sources within which supplemental planting would be unnecessary to meet tree stocking objectives. [source] Traits, neighbors, and species performance in prairie restorationAPPLIED VEGETATION SCIENCE, Issue 3 2010R.E. Roberts Abstract Questions: Are traits related to the performance of plant species in restoration? Are the relationships between traits and performance consistent across the functional groups of annual forbs, perennial forbs and grasses? Do the relationships between traits and performance depend on neighboring functional groups? Location: A former agricultural field, being restored to native upland prairie, in the Willamette Valley of western Oregon, USA. Methods: Twenty-eight native species, representing three functional groups, were sown in seven different combinations. Eleven functional traits were measured from plants in the laboratory and in the field. Correlations between individual traits and performance variables were measured and regression techniques used to determine which sets of traits were most strongly related to performance. Results: Sets of traits explained up to 56% of variation in cover, and up to 48% of variation in establishment frequency. The relationships between traits and performance were influenced by functional group identity; the functional group identity of neighboring species also influenced species' cover and the relationships between traits and cover. Species' establishment rate in monoculture was the trait most strongly correlated to both establishment and cover in mixtures. In multi-trait models, annual forb functional group identity was strongly related to establishment in mixtures, and height, leaf weight ratio at 7 d and seed mass were strongly related to cover. Conclusions: Multiple-trait models should be a useful way of predicting the performance of species prior to sowing in restoration. The functional group identity of each species and the other species being sown may need to be taken into account when making predictions. [source] The measurement and modelling of rill erosion at angle of repose slopes in mine spoilEARTH SURFACE PROCESSES AND LANDFORMS, Issue 7 2008G. R. Hancock Abstract The process of rill erosion causes significant amounts of sediment to be moved in both undisturbed and disturbed environments and can be a significant issue for agriculture as well as mining lands. Rills also often develop very quickly (from a single rainfall event to a season) and can develop into gullies if sufficient runoff is available to continue their development. This study examines the ability of a terrestrial laser scanner to quantify rills that have developed on fresh and homogeneous mine spoil on an angle of repose slope. It also examines the ability of the SIBERIA erosion model to simulate the rill's spatial and temporal behaviour. While there has been considerable work done examining rill erosion on rehabilitated mine sites and agricultural fields, little work has been done to examine rill development at angle of repose sites. Results show that while the overall hillslope morphology was captured by the laser scanner, with the morphology of the rills being broadly captured, the characteristics of the rills were not well defined. The digital elevation model created by the laser scanner failed to capture the rill thalwegs and tops of the banks, therefore delineating a series of ill defined longitudinal downslope depressions. These results demonstrate that an even greater density of points is needed to capture sufficient rill morphology. Nevertheless, SIBERIA simulations of the hillslope demonstrated that the model was able to capture rill behaviour in both space and time when correct model parameters were used. This result provides confidence in the SIBERIA model and its parameterization. The results demonstrate the sensitivity of the model to changes in parameters and the importance of the calibration process. Copyright © 2007 John Wiley & Sons, Ltd. [source] Starling foraging success in relation to agricultural land-useECOGRAPHY, Issue 3 2002Ola Olsson Changes in agricultural land-use have been suggested to contribute to the decline of several bird species through negative effects on their food supply during breeding. One important change in land-use has been loss of pastures, especially permanent pastures. In this study we investigated how different forms of agricultural land-use affected foraging success of a declining bird species, the European starling Sturnus vulgaris. We let caged starlings forage in different forms of agricultural fields and determined time spent foraging and foraging success. The starlings' activity level (time spent actively foraging) as well as the number of prey caught per time unit was strongly related to the abundance of prey in soil samples. Also the body mass change during the experiment was positively related to activity level and prey capture rate. We found consistent differences in foraging variables between habitats. In spring sown grain starlings were least active and found fewer prey items at a lower rate than in any other habitat. The other three habitats differed less, but in general mowed hay fields appeared slightly more valuable than the cultivated and natural pastures. We did not find any differences between natural and cultivated pastures in foraging variables. Thus, starling foraging success is higher in grass-covered fields than in cultivated fields, but the management of the grass-covered fields mattered less. The results are consistent with starlings having higher population densities and breeding success in areas with higher availability of pasture. We suggest that the physical structure of the habitat (sward height) and moisture may be additional variables that need to be taken into account to explain starling breeding density and success in the agricultural landscape. [source] A cross-ecosystem comparison of the strength of trophic cascadesECOLOGY LETTERS, Issue 6 2002Jonathan B. Shurin Abstract Although trophic cascades (indirect effects of predators on plants via herbivores) occur in a wide variety of food webs, the magnitudes of their effects are often quite variable. We compared the responses of herbivore and plant communities to predator manipulations in 102 field experiments in six different ecosystems: lentic (lake and pond), marine, and stream benthos, lentic and marine plankton, and terrestrial (grasslands and agricultural fields). Predator effects varied considerably among systems and were strongest in lentic and marine benthos and weakest in marine plankton and terrestrial food webs. Predator effects on herbivores were generally larger and more variable than on plants, suggesting that cascades often become attenuated at the plant,herbivore interface. Top-down control of plant biomass was stronger in water than on land; however, the differences among the five aquatic food webs were as great as those between wet and dry systems. [source] Emission of legacy chlorinated pesticides from agricultural and orchard soils in British Columbia, CanadaENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 6 2006Terry F. Bidleman Abstract Air samples were collected above agricultural fields in the Fraser Valley and orchards in the Okanagan Valley, British Columbia, Canada, to investigate volatilization of organochlorine pesticides used in the past. Concentrations of pesticides in air were elevated over soils that contained higher residues. Soil/air fugacity ratios at sites with the higher soil residues were calculated relative to air sampled at 40 cm height and background air. The fugacity ratios in the first case indicated net volatilization or soil-air equilibrium for most compounds and occasional net deposition for p,p, -dichlorodiphenyldichloroethene (p,p, -DDE), whereas those in the second case showed a strong potential for net volatilization of all compounds. The enantiomer fraction (EF) of chiral compounds ,-hexachlorocyclohexane (,-HCH), trans -chlordane, cis -chlordane, and o,p, -DDT were determined in overlying air samples and soils. Enantiomer fractions in air corresponded to those in soils at fields in which soil concentrations were high but were decoupled from soil signatures at fields with low soil residues. Mean EFs in air sampled over soils were significantly (p < 0.001) nonracemic for ,-HCH and the chlordanes and agreed with published EFs in regional ambient air. The mean EF of o,p, -DDT for all air samples did not show a significant deviation from racemic EFs (p > 0.2), but EFs of individual samples reflected the ambivalent nature of o,p, -DDT degradation, sometimes preferring the (+) enantiomer and other times the (,) enantiomer. The study indicates that soils are continuing to emit "legacy" pesticides into the regional atmosphere. [source] Estimating the probability of bird mortality from pesticide sprays on the basis of the field study recordENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 7 2002Pierre Mineau Abstract The outcome of avian field studies was examined to model the likelihood of mortality. The data were divided into clusters reflecting the type of pesticide application and bird guilds present on site. Logistic regression was used to model the probability of a bird kill. Four independent variables were tested for their explanatory power: a variable reflecting acute oral toxicity and application rate; a variable reflecting the relative oral to dermal toxicity of the pesticides; Henry's law constant; and a variable reflecting possible avoidance of contaminated food items, the hazard factor (HF). All variables except for HF significantly improved model prediction. The relative dermal to oral toxicity, especially, was shown to have a major influence on field outcome and clearly must be incorporated into future avian risk assessments. The probability of avian mortality could be calculated from a number of current pesticide applications and the conclusion was made that avian mortality occurs regularly and frequently in agricultural fields. [source] Microbial degradation of isoproturon and related phenylurea herbicides in and below agricultural fieldsFEMS MICROBIOLOGY ECOLOGY, Issue 1 2003Sebastian R Sørensen Abstract The phenylurea herbicides are an important group of pesticides used extensively for pre- or post-emergence weed control in cotton, fruit and cereal crops worldwide. The detection of phenylurea herbicides and their metabolites in surface and ground waters has raised the awareness of the important role played by agricultural soils in determining water quality. The degradation of phenylurea herbicides following application to agricultural fields is predominantly microbial. However, evidence suggests a slow degradation of the phenyl ring, and substantial spatial heterogeneity in the distribution of active degradative populations, which is a key factor determining patterns of leaching losses from agricultural fields. This review summarises current knowledge on the microbial metabolism of isoproturon and related phenylurea herbicides in and below agricultural soils. It addresses topics such as microbial degradation of phenylurea herbicides in soil and subsurface environments, characteristics of known phenylurea-degrading soil micro-organisms, and similarities between metabolic pathways for different phenylurea herbicides. Finally, recent studies in which molecular and microbiological techniques have been used to provide insight into the in situ microbial metabolism of isoproturon within an agricultural field will be discussed. [source] Quantifying carbon sequestration as a result of soil erosion and deposition: retrospective assessment using caesium-137 and carbon inventoriesGLOBAL CHANGE BIOLOGY, Issue 12 2007TIMOTHY ANDREW QUINE Abstract The role of soil erosion in the global carbon cycle remains a contested subject. A new approach to the retrospective derivation of erosion-induced quantitative fluxes of carbon between soil and atmosphere is presented and applied. The approach is based on the premise that soil redistribution perturbs the carbon cycle by driving disequilibrium between soil carbon content and input. This perturbation is examined by establishing the difference between measured carbon inventories and the inventories that would be found if input and content were in dynamic equilibrium. The carbon inventory of a profile in dynamic equilibrium is simulated by allowing lateral and vertical redistribution of carbon but treating all other profile inputs as equal to outputs. Caesium-137 is used to derive rates of vertical and lateral soil redistribution. Both point and field-scale estimates of carbon exchange with the atmosphere are derived using the approach for a field subject to mechanized agricultural in the United Kingdom. Sensitivity analysis is undertaken and demonstrates that the approach is robust. The results indicate that, despite a 15% decline in the carbon content of the cultivation layer of the eroded part of the field, this area has acted as a net sink of 11 ± 2 g C m,2 yr,1 over the last half century and that in the field as a whole, soil redistribution has driven a sink of 7 ± 2 g C m,2 yr,1 (6 ± 2 g C m,2 yr,1 if all eroded carbon transported beyond the field boundary is lost to the atmosphere) over the same period. This is the first empirical evidence for, and quantification of, dynamic replacement of eroded carbon. The relatively modest field-scale net sink is more consistent with the identification of erosion and deposition as a carbon sink than a carbon source. There is a clear need to assemble larger databases with which to evaluate critically the carbon sequestration potential of erosion and deposition in a variety of conditions of agricultural management, climate, relief, and soil type. In any case, this study demonstrated that the operation of erosion and deposition processes within the boundaries of agricultural fields must be understood as a key driver of the net carbon cycle consequences of cultivating land. [source] Dynamics of suspended sediment transport at field-scale drain channels of irrigation-dominated watersheds in the Sonoran Desert, southeastern CaliforniaHYDROLOGICAL PROCESSES, Issue 16 2007Peng Gao Abstract Suspended sediment is a major source of pollution in irrigation-dominated watersheds. However, little is known about the process and mechanisms of suspended sediment transport in drain channels directly connected to agricultural fields. This paper explains sediment dynamics using averaged 5 min flow discharge Q (m3 s,1) and suspended sediment concentration C (mg l,1) collected during one crop season in a small catchment containing a first-order drain channel and its connected six agricultural fields within the Salton Sea watershed. The statistical properties and average trends of Q and C were investigated for both early (i.e. November) and late (i.e. January) stages of a crop season. Further in-depth analysis on sediment dynamics was performed by selecting two typical single-field irrigation events and two multiple-field irrigation events. For each set of irrigation events, the process of suspended sediment transport was revealed by examining hydrograph and sediment graph responses. The mechanisms underlying suspended sediment transport were investigated by analysing the types of corresponding hysteresis loop. Finally, sediment rating curves for both hourly and daily data at early and late stages and for the entire crop season were established to seek possible sediment-transport predictive model(s). The study suggests that the complicated processes of suspended sediment transport in irrigation-dominated watersheds require stochastic rather than deterministic forecasting. Copyright © 2007 John Wiley & Sons, Ltd. [source] Development of the herbivore Pieris rapae and its endoparasitoid Cotesia rubecula on crucifers of field edgesJOURNAL OF APPLIED ENTOMOLOGY, Issue 9-10 2006J. A. Harvey Abstract:, Several studies have reported that flowering herbs, which grow naturally or are sown adjacent to agricultural fields, may be an important source of nutrients for natural enemies. Many parasitoids readily feed on plant exudates such as floral nectar, which contain different types of sugars that enable the insects to optimize their longevity, mobility and reproductive success. However, leaf tissues of plants grown in the margins of agricultural fields may also provide food for immature stages of insect herbivores, such as caterpillars, that are in turn attacked by parasitoids. Herbivores and their parasitoids may later disperse into the crop, so the nutritional quality of surrounding plants, as this affects herbivore and parasitoid fitness, may also influence the success of biological control programmes, especially later in the season. Here, we compare the suitability of three species of cruciferous plants (Brassicaceae) on the development of Pieris rapae L. (Lep., Pieridae) and its solitary endoparasitoid, Cotesia rubecula Marshall (Hym., Bracondiae). Insects were reared on a feral population of cabbage, Brassica oleracea, on radish Raphanus sativus, which is widely sown in agricultural margins, and on hedge mustard, Sisymbrium officinale, a wild crucifer which often grows in medium to large stands along road verges and field edges. Development time in both the herbivore and parasitoid were extended on R. sativus, compared with the other two species, whereas C. rubecula completed its development most rapidly on B. oleracea. Moreover, adult butterflies and parasitoids were significantly smaller when reared on R. sativus plants. Our results reveal that differences in the quality of plants growing adjacent to agricultural fields can affect the development of key herbivores and their parasitoids. This should be borne in mind when establishing criteria for the selection of floral biodiversity. [source] How did common ragweed (Ambrosia artemisiifolia L.) spread in Québec?JOURNAL OF BIOGEOGRAPHY, Issue 10 2007A historical analysis using herbarium records Abstract Aim, To reconstruct the spread of common ragweed (Ambrosia artemisiifolia L.; Asteraceae) using herbarium specimens to document whether the habitat preferences of this plant have shifted through time. Location, Southern Québec. Methods, Herbarium specimens stored in the main herbaria of southern Québec were used to reconstruct the spread of common ragweed. All data (sampling location, year of sampling, habitat characteristics, etc.) were incorporated into a geographical information system. Maps indicating the spatial distribution of common ragweed were produced for four time periods. The cumulative number of locations was plotted against time to construct invasion curves. The sequence of habitats where herbarium specimens were collected was also reconstructed. Results, A data base incorporating 707 common ragweed herbarium specimens was constructed for this study. The spread of common ragweed in most regions of southern Québec was initiated at the beginning of the 20th century. Herbarium specimens suggest that common ragweed first spread along river corridors. Specimens of common ragweed were not collected in agricultural fields before the mid-1920s, nor along roads and railways before the mid-1930s. The colonization of a large number of agricultural fields by common ragweed probably began with seed-contaminated crops, but was certainly accelerated by the dispersal of seeds from populations growing along nearby roads. Main conclusions, Herbarium specimens suggest that common ragweed has been present in southern Québec for at least 200 years, but the species was probably restricted to the Montréal area during the 19th century. It is likely that the development of the road network in Québec since the mid-1930s significantly contributed to the spread of common ragweed. Controlling common ragweed solely in agricultural fields would not prevent the re-infestation of crops, because roadsides would act as refuges for the weed. [source] Scattered trees as modifiers of agricultural landscapes: the role of waddeessa (Cordia africana Lam.) trees in Bako area, Oromia, EthiopiaAFRICAN JOURNAL OF ECOLOGY, Issue 2009Abebe Yadessa Abstract Scattered trees in general and scattered waddeessa (Cordia africana Lam.) trees in particular are very common across the agricultural landscapes in Oromia, Ethiopia. A study on this scattered waddeessa trees commonly growing on farmers' agricultural fields was conducted at Bako in western Oromia, Ethiopia with the objective of assessing their role in modifying the soil properties in the agricultural landscape. Soil samples from surface layers (0,10 cm) were taken at three concentric transects (0.5, 2 and 4 m) around the tree and compared with soil samples from the adjacent open areas (15 m distance from the tree), and then analysed following the standard procedures. Results showed that scattered waddeessa trees significantly modified the overall properties of the soil in the agricultural landscape of Bako area. But soil texture was not affected, indicating that it is more related to parent material than the tree influence. Hence, the soil patches observed under these waddeessa trees can be important local nutrient reserves that may influence the rural agricultural landscape. They also play an important role in generating local household income from the sale of products and conserving biodiversity by providing habitats and resources that are otherwise absent or scarce in agricultural landscape. [source] Homogenization of forest plant communities and weakening of species,environment relationships via agricultural land useJOURNAL OF ECOLOGY, Issue 3 2007MARK VELLEND Summary 1Disturbance may cause community composition across sites to become more or less homogenous, depending on the importance of different processes involved in community assembly. In north-eastern North America and Europe local (alpha) diversity of forest plants is lower in forests growing on former agricultural fields (recent forests) than in older (ancient) forests, but little is known about the influence of land-use history on the degree of compositional differentiation among sites (beta diversity). 2Here we analyse data from 1446 sites in ancient and recent forests across 11 different landscapes in north-eastern North America and Europe to demonstrate decreases in beta diversity and in the strength of species,environment relationships in recent vs. ancient forests. 3The magnitude of environmental variability among sites did not differ between the two forest types. This suggests the difference in beta diversity between ancient and recent forests was not due to different degrees of environmental heterogeneity, but rather to dispersal filters that constrain the pool of species initially colonizing recent forests. 4The observed effects of community homogenization and weakened relationships between species distributions and environmental gradients appear to persist for decades or longer. The legacy of human land-use history in spatial patterns of biodiversity may endure, both within individual sites and across sites, for decades if not centuries. [source] Ectomycorrhizal fungal communities at forest edgesJOURNAL OF ECOLOGY, Issue 2 2005IAN A. DICKIE Summary 1Ectomycorrhizal fungi are spatially associated with established ectomycorrhizal vegetation, but the influence of distance from established vegetation on the presence, abundance, diversity and community composition of fungi is not well understood. 2We examined mycorrhizal communities in two abandoned agricultural fields in Minnesota, USA, using Quercus macrocarpa seedlings as an in situ bioassay for ectomycorrhizal fungi from 0 to 20 m distance from the forest edge. 3There were marked effects of distance on all aspects of fungal communities. The abundance of mycorrhiza was uniformly high near trees, declined rapidly around 15 m from the base of trees and was uniformly low at 20 m. All seedlings between 0 and 8 m distance from forest edges were ectomycorrhizal, but many seedlings at 16,20 m were uninfected in one of the two years of the study. Species richness of fungi also declined with distance from trees. 4Different species of fungi were found at different distances from the edge. ,Rare' species (found only once or twice) dominated the community at 0 m, Russula spp. were dominants from 4 to 12 m, and Astraeus sp. and a Pezizalean fungus were abundant at 12 m to 20 m. Cenococcum geophilum, the most dominant species found, was abundant both near trees and distant from trees, with lowest relative abundance at intermediate distances. 5Our data suggest that seedlings germinating at some distance from established ectomycorrhizal vegetation (15.5 m in the present study) have low levels of infection, at least in the first year of growth. Distance from established vegetation represents an important gradient for ectomycorrhizal fungi, with different species occupying distinct niches along this gradient. This provides support for niche differentiation as a factor contributing to ectomycorrhizal fungal diversity. 6Ectomycorrhizal infection of seedlings is spatially complex, with high infection and high fungal diversity near trees, high infection but lower diversity at intermediate distances, and low infection and low fungal diversity distant from trees. This spatial complexity should be considered as a factor potentially influencing the establishment of ectomycorrhizal vegetation. [source] Coverage path planning algorithms for agricultural field machinesJOURNAL OF FIELD ROBOTICS (FORMERLY JOURNAL OF ROBOTIC SYSTEMS), Issue 8 2009Timo Oksanen In this article, a coverage path planning problem is discussed in the case of agricultural fields and agricultural machines. Methods and algorithms to solve this problem are developed. These algorithms are applicable to both robots and human-driven machines. The necessary condition is to cover the whole field, and the goal is to find as efficient a route as possible. As yet, there is no universal algorithm or method capable of solving the problem in all cases. Two new approaches to solve the coverage path planning problem in the case of agricultural fields and agricultural machines are presented for consideration. Both of them are greedy algorithms. In the first algorithm the view is from on top of the field, and the goal is to split a single field plot into subfields that are simple to drive or operate. This algorithm utilizes a trapezoidal decomposition algorithm, and a search is developed of the best driving direction and selection of subfields. This article also presents other practical aspects that are taken into account, such as underdrainage and laying headlands. The second algorithm is also an incremental algorithm, but the path is planned on the basis of the machine's current state and the search is on the next swath instead of the next subfield. There are advantages and disadvantages with both algorithms, neither of them solving the problem of coverage path planning problem optimally. Nevertheless, the developed algorithms are remarkable steps toward finding a way to solve the coverage path planning problem with nonomnidirectional vehicles and taking into consideration agricultural aspects. © 2009 Wiley Periodicals, Inc. [source] Glutamate Fermentation By-product Activates Plant Defence Responses and Confers Resistance Against Pathogen InfectionJOURNAL OF PHYTOPATHOLOGY, Issue 10 2010Daisuke Igarashi Abstract In the food industry, glutamate fermentation by-product (GFB) is generated by purifying glutamate products from microbial fermentation. The potential applications of GFB for upgrading agricultural soil, for foliar fertility, and as plant plankton for shrimp have been studied. We examined the efficacy of GFB foliar application and determined that GFB treatment increased the resistance of Arabidopsis leaves to infection by bacterial pathogens. Microarray gene expression analysis of Arabidopsis leaves after treatment with GFB indicated that the expression of plant defence-related genes increased. In Corynebacterium fermentation, the active substances for induction of the defence response were extracted or solubilized after treatment with heating under acidic conditions. This extract was also effective in strawberry and grape leaves for the induction of hydrogen peroxide production. These findings suggest that foliar application of GFB that contains elicitor molecules derived from fermentation bacteria is useful for plant protection in agricultural fields. [source] | ||||||||||||||||||||||||||||||||||