Wet Spring Conditions Research Articles

Stories of a water-table: anomalous depressions, aquitard breaches and seasonal implications, Shelby County, Tennessee, USA

An extensive water level survey of the water-table aquifer (i.e., shallow aquifer) within Shelby County, Tennessee, was conducted in the dry (fall 2020) and wet (spring 2021) seasons. Water-table surfaces were generated using cokriging to observe seasonal differences to identify anomalous water-table depressions, indicative of an underlying aquitard breach. Seasonal differences were attributed to non-coincident control and timing between the surveys and when optimum dry (fall) and wet (spring) conditions existed, as observed through comparisons with continuous historical water levels from 12 shallow monitoring wells. Additionally, data from fall 2020 were compared to previous studies in 2005 and 2015 to determine decadal changes in levels and shape of the water-table surface which were mostly attributed to changes in data control and potential climate variations. A prediction error map was generated from the 2020 dataset to identify areas of the county with high-prediction error (>7.0 m) to offer guidance on where future well control would be optimal.

Management Effects on the Performance of Double Cropping Systems—Results from a Multi-Site Experiment

Traditional (silage) maize production often has negative side-effects related to unprotected soil surface. There are several possibilities to enhance system sustainability through reducing soil disturbance. However, implementation may be hindered due to reduced nitrogen availability and increased weed infestation, especially in organic agriculture. A field experiment to evaluate yield potential of 18 silage maize cropping systems under organic management was conducted at three distinct locations. Examined parameters were first crop, maize and total harvested dry matter yield (DMY), and maize dry matter content (DMC). Treatment factors included first crop (FC—winter pea, hairy vetch, and their mixtures with rye, control (SCS), management—incorporating FC use and tillage (double cropping system no-till (DCS NT), double cropping system reduced till (DCS RT), double cropped, mulched system terminated with roller-crimper (DCMS Roll), SCS control), fertilization, mechanical weed control—and row width (75 cm, 50 cm). A high variation among environments occurred, but similar patterns manifested across locations: Number of crops in the rotation had a high influence, followed by management and FC. Row width had only marginal and inconsistent effect. FC mixtures generally yielded higher than pure legumes. Maize DMY in DCS, DCMS was lower than or comparable to SCS. Maize DMC were environment-specifically below acceptable range, especially under DCMS. Total harvested DMY in DCS were similar to or greater than SCS. Results suggest differences from the optimization of farming operations for one (SCS) or two crops (DCS, DCMS) with strong effects at early maize development and on the length of season. FC use and tillage factors possibly altered the soil water, temperature, and mineralization dynamics, resulting in modified maize growth. DCS RT and DCMS Pure performed with the best maize yields, improved soil protection, and tillage reduction in the silage maize part of the rotation under organic management. However, alternative management systems, especially under DCS NT and DCMS (Mix) with studied maize maturity classes are less suited, particularly in cool and wet spring conditions, because of a potentially slower development of FC, a later establishment of maize plants and therefore, a shorter growing season for the maize crop.

Grazing winter rye cover crop in a cotton no‐till system: Soil strength and runoff

AbstractGrazing cover crops (CC) could provide an economic incentive to increase adoption rates in the southeastern United States. However, understanding grazing effects on soil properties is lacking for most soils of the region. Effects of grazing or rolling a cereal rye (Secale cereale L.) CC prior to no‐till planting cotton (Gossypium hirsutum L.) were determined in 2009 after 4 yr on Cecil soil, in the Southern Piedmont near Watkinsville, GA. The four catchments had a previous long history of no‐till cropping with CC. Wet spring conditions in 2009 resulted in visible surface roughness from cattle hooves. Average soil penetration resistance (PR) for the 0‐ to 30‐cm profile was 14% greater following rye CC grazing than rolling (1.95 vs. 1.53 MPa) and was still apparent the following February (1.86 vs. 1.58 MPa) after cotton harvest. Increases in PR at 2.5‐ to 7.5‐ and 7.5‐ to 15‐cm soil depths were observed following CC grazing but not rolling. Depth to 2 MPa resistance, considered sufficient to impede root growth, was similar for CC grazing and rolling treatments in March prior to grazing but decreased in the grazed treatment to 10.7 cm in May and 15.6 cm in February. Seasonal runoff data for 2006–2009 indicated no differences between grazed and rolled CC management. We concluded that grazing CC for short periods under wet conditions presents a risk of short‐term negative effects even for Southern Piedmont soils where a long history of conservation tillage and CC has improved soil quality.

Nitrate leaching and nitrous oxide emissions from maize after grass-clover on a coarse sandy soil: Mitigation potentials of 3,4-dimethylpyrazole phosphate (DMPP)

Cropping of maize (Zea mays L.) on sandy soil in wet climates involves a significant risk for nitrogen (N) losses, since nitrate added in fertilizers or produced from residues and manure may be lost outside the period with active crop N uptake. This one-year lysimeter experiment investigated the potential of Vizura®, a formulation for liquid manure (slurry) with the nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP), to mitigate nitrous oxide (N2O) emissions and nitrate (NO3−) leaching from a coarse sandy soil cropped with maize. Maize followed grass-clover (Lolium perenne L.-Trifolium pratense L.) with spring incorporation and was fertilised with cattle slurry. A total of 12 treatments in triplicate were included in a factorial experiment with 1 m2 large and 1.4 m deep lysimeters: 1) with or without spraying the above-ground biomass of grass-clover with DMPP before incorporation; 2) application of cattle manure with or without DMPP, or no fertilization; and 3) natural rainfall or extra rain events to represent wet spring conditions, which were simulated with an automated and programmable irrigation system. Around 20 kg N ha−1 was returned to the soil in grass-clover above-ground biomass, and 145 kg N ha−1 in cattle manure. Cumulative annual N2O emissions ranged from 0.4 to 1.3 kg N ha−1, with between 49 and 86% of emissions occurring during spring. Manure application increased N2O emissions, while extra rainfall had no effect. The mitigation of N2O emissions by DMPP ranged from 46 to 67% under natural, and from 44 to 48% under high rainfall conditions. Total annual NO3− leaching ranged from 65 to 162 kg N ha−1. The extent of NO3− leaching to 1.4 m depth during spring was low, and instead most (72–83%) of total annual NO3−-N leaching was recorded during autumn before harvest. The extra rainfall during spring increased NO3−-N leaching in the pre-harvest period, but it is not clear to what extent this was associated with the N in grass-clover residues or manure applied in spring, or from N mineralisation below the root zone. Despite evidence for a reduction of NO3− leaching in three of four scenarios, overall this effect was not significant. No DMPP was detected in leachates. In conclusion, DMPP significantly reduced N2O emissions from cattle manure on this sandy loam soil independent of rainfall, while there was no significant effect on NO3− leaching. The results indicate that N2O emissions and NO3−-N leaching were partly derived from below-ground sources of N not affected by DMPP, which should be further investigated to better predict the mitigation potential of nitrification inhibitors.

Seasonal ground ice impacts on spring ecohydrological conditions in a western boreal plains peatland

AbstractPeatlands in the Western Boreal Plains act as important water sources in the landscape. Their persistence, despite potential evapotranspiration (PET) often exceeding annual precipitation, is attributed to various water storage mechanisms. One storage element that has been understudied is seasonal ground ice (SGI). This study characterized spring SGI conditions and explored its impacts on available energy, actual evapotranspiration, water table, and near surface soil moisture in a western boreal plains peatland. The majority of SGI melt took place over May 2017. Microtopography had limited impact on melt rates due to wet conditions. SGI melt released 139mm in ice water equivalent (IWE) within the top 30cm of the peat, and weak significant relationships with water table and surface moisture suggest that SGI could be important for maintaining vegetation transpiration during dry springs. Melting SGI decreased available energy causing small reductions in PET (<10mm over the melt period) and appeared to reduce actual evapotranspiration variability but not mean rates, likely due to slow melt rates. This suggests that melting SGI supplies water, allowing evapotranspiration to occur at near potential rates, but reduces the overall rate at which evapotranspiration could occur (PET). The role of SGI may help peatlands in headwater catchments act as a conveyor of water to downstream landscapes during the spring while acting as a supply of water for the peatland. Future work should investigate SGI influences on evapotranspiration under differing peatland types, wet and dry spring conditions, and if the spatial variability of SGI melt leads to spatial variability in evapotranspiration.

The decline of Algerian Cedrus atlantica forests is driven by a climate shift towards drier conditions

Some north-African Atlas cedar (Cedrus atlantica) forests are in decline, following decades of anthropogenic pressure and repeated drought events. We investigated if the recent decline episodes of these forests are linked to precipitation and temperature shifts, leading to a reduction in tree radial growth and climate-growth uncouplings. Tree-ring width chronologies of Atlas cedar in north-western Algeria allow the identification of climate and growth shifts in these vulnerable Mediterranean forests. Such chronologies, built for six sites, showed common patterns of year-to-year variability during the period 1910-2006. The growth at north-facing sites declined from the 1980s until 2006, whereas the growth at mid-elevation sites declined from the early 20th century until the 1940s, remained stable until the 1980s and then declined until 2006. Cool and wet spring conditions enhanced cedar growth. Sites with fast-growing trees, where growth was strongly reduced by dry summer conditions, showed the most-pronounced negative trends. However, a clear climate-growth uncoupling was observed after the 1970s, when the climate rapidly warmed. We also detected a negative growth shift in the 1980s, when mortality increased. This coincided with changes in early-warning signals of the growth series, such as an increase in the first-order autocorrelation of tree-ring width. All these lines of evidence indicate that the 1980s climate shift towards warmer and drier conditions triggered a shift in cedar growth. The use of radial-growth series as early-warning signals should be further investigated in this species and in other drought-sensitive conifers, given the aridification trends expected for the Mediterranean Basin.

Basalt Milkvetch Responses to Novel Restoration Treatments in the Great Basin

The restoration of native forbs in the Great Basin and similar dryland ecosystems remains a great challenge for land managers. Variable soil water, precocious germination and emergence, and the presence of soil fungal pathogens often reduce plant establishment. Novel restoration treatments that increase soil water during early forb life stages, delay germination and emergence to coincide with favorable spring conditions, and reduce mortality from soil fungal pathogens may benefit native forb restoration. We compared the efficacy of three novel treatments—snow fencing, plant protection fabric, and seed coatings—to improve establishment of a forb species native to the Great Basin, basalt milkvetch (Astragalus filipes Torr. ex A. Gray). We replicated treatments plus a no-treatment control at three sites in the Great Basin in a randomized complete block design over 2 yr. To evaluate the efficacy of our restoration treatments, we measured germination, seedling emergence, establishment, and second-yr survival. The effects of snow fencing and plant protection fabric varied by site and life stage and were likely influenced by the wet spring conditions across sites, particularly the two northern sites. Snow fencing increased establishment and second-yr survival at one site. Plant protection fabric did not benefit any life stage at any site. Seed coatings increased seedling emergence at all sites but did not affect establishment or survival. Overall, second-yr survival remained low across all sites and treatments. Our study indicates that our treatments can positively affect basalt milkvetch emergence, establishment, and survival, but additional management actions are needed to improve long-term restoration success of native forbs.

Hydroclimatological Drivers of Extreme Floods on Lake Ontario

AbstractThis study examines the hydrologic and climatic conditions that precede major flood events on Lake Ontario, with the purpose of understanding the potential for seasonal forecasts to inform lake level management. Seven late spring/early summer flood events are identified since 1949, including the record‐breaking flood of 2017. The surface climate, atmospheric circulation, and antecedent lake levels for the preceding winter and spring seasons are examined. Results suggest that flood events are caused by different combinations of high, initial wintertime water levels across all of the Great Lakes, anomalously wet winters across the entire Great Lakes basin, and wet spring conditions, particularly in the eastern part of the basin. Wet winters that precede flood events are often associated with La Niña conditions, while wet springs are often associated with a westward shift of the North Atlantic Subtropical High. As the critical drawdown period for Lake Ontario occurs in the fall, before the onset of anomalous winter or spring/summer inputs, a generalized additive model was used to predict April–August maximum monthly average Lake Ontario water levels using November levels for all Great Lakes, a nonlinear response to the wintertime Niño 3.4 index, and scenarios of April–May overbasin precipitation. The Niño 3.4 index significantly improves lake level predictions, suggesting that an El Niño‐Southern Oscillation signal may be useful for lake level management. Future work needed to verify the use of El Niño‐Southern Oscillation for Lake Ontario flood forecasting and to link the North Atlantic Subtropical High to predictions of springtime Great Lakes climate is discussed.

Synoptic weather conditions and changing fire regimes in a Mediterranean environment

Analysis of global change effects on fire regimes requires evaluations of key processes explaining fire activity at the appropriate spatial and temporal scales. Classifications of the weather conditions prevailing at large continental scales (called “Synoptic Weather Types”, SWT) offer convenient potential proxies for integrating weather-related factors into our understanding of fire regime attributes at regional scales. Here we establish a methodology for identifying the major SWT that lead to wildfires and assessing their influence on fire regime in interaction with other global drivers such as drought events or fire suppression policies. Based on days with fires larger than 50 ha that occurred in Catalonia, a region located in the western Mediterranean Basin, we propose a clustering methodology using data of temperature at 850 hPa, sea level pressure and winds at 925 hPa from the NCEP/NCAR reanalysis dataset covering the whole of western Europe (25–70°N and 20°W–40°E). Our classification method proposes 6 SWT: three that were characterized by synoptic conditions leading to strong winds in the region, two that led to ‘hot and dry’ environments, and one that was not characterized by any strong weather determinants. Fires under ‘hot and dry’ conditions, such as the South intrusion SWT, triggered the bulk of fires and burnt area in the region. Spatial analyses of fire distribution under each SWT revealed markedly different fire-prone locations, opening the possibility for strategic planning of fire management based on local fire regimes. Fires occurring during mild years (wet spring conditions) and under ‘hot-and-dry’ SWTs have been eradicated from the region thanks to enhanced firefighting capability, and fire sizes in dry years have strongly reduced. In contrast, fires occurring under windy situations have not followed the same course of change and have not diminished in incidence over time, and seem to be more difficult to control using current fire suppression strategies. The role of SWT on determining fire regimes and its interaction with fire suppression strategies has a huge potential to help researchers and managers develop better fire analyses based on sound physical grounds and serve to understand and eventually regulate the adverse impacts of fire regime changes in a global change context.

Planting and harvest dates, and irrigation on fenugreek in the semi-arid high plains of the USA

Fenugreek can be grown for medicinal purposes, as a spice or as an annual hay. Most fenugreek production is in India; none is grown in the USA. Practices suitable for growing fenugreek in the U.S. High Plains is unknown. The objectives were to identify the irrigation need, and planting and harvest dates in western Nebraska. Fenugreek was planted from early May to early June and harvested from late Aug to early Oct. Irrigation consisted of none, 15 and 30cm. Height, flowering and fruiting, and seed and straw yields were measured. Later planting did not affect final height but delayed flowering and fruiting (late June to early Aug). Years differed due to weather variations. Seed and straw yields were greatest with later planting and with earlier harvest in 2013 and 2014. Irrigation affected yields primarily in 2013. The lowest yields were in 2015 when the agronomic parameters had the least effect probably due to the very wet spring conditions. For 2013 and 2014, maximum seed yields ranged from 1724 to 1886kgha−1, and maximum straw yields ranged from 4352 to 4981kgha−1 when planted late, irrigated and harvested in late Aug or early Sep. Recommendations are that when May is very dry, plant near 1 June, irrigate and harvest in late Aug or early Sep, when May is slightly wet, plant in late May, do not irrigate and harvest early Sep, and when May is very wet, do not plant for seed and do not irrigate.

Wood anatomy and carbon-isotope discrimination support long-term hydraulic deterioration as a major cause of drought-induced dieback.

Hydraulic impairment due to xylem embolism and carbon starvation are the two proposed mechanisms explaining drought-induced forest dieback and tree death. Here, we evaluate the relative role played by these two mechanisms in the long-term by quantifying wood-anatomical traits (tracheid size and area of parenchyma rays) and estimating the intrinsic water-use efficiency (iWUE) from carbon isotopic discrimination. We selected silver fir and Scots pine stands in NE Spain with ongoing dieback processes and compared trees showing contrasting vigour (declining vs nondeclining trees). In both species earlywood tracheids in declining trees showed smaller lumen area with thicker cell wall, inducing a lower theoretical hydraulic conductivity. Parenchyma ray area was similar between the two vigour classes. Wet spring and summer conditions promoted the formation of larger lumen areas, particularly in the case of nondeclining trees. Declining silver firs presented a lower iWUE than conspecific nondeclining trees, but the reverse pattern was observed in Scots pine. The described patterns in wood anatomical traits and iWUE are coherent with a long-lasting deterioration of the hydraulic system in declining trees prior to their dieback. Retrospective quantifications of lumen area permit to forecast dieback in declining trees 2-5 decades before growth decline started. Wood anatomical traits provide a robust tool to reconstruct the long-term capacity of trees to withstand drought-induced dieback.

Snow cover, freeze‐thaw, and the retention of nutrients in an oceanic mountain ecosystem

As the climate warms, winters with less snow and therefore more soil freeze‐thaw cycles are likely to become more frequent in oceanic mountain areas. It is a concern that this might impair the soil's ability to store carbon and nutrients, and lead to increased leaching losses of dissolved C and nutrients and subsequent changes in nutrient cycling and ecosystem productivity.Through a combination of laboratory and field experiments, we studied short‐term effects of changing winter conditions on carbon and nutrient leaching from two plant‐soil systems with contrasting snow conditions (shallow/intermittent vs. deep/persistent snow). In the laboratory we exposed cores (soil and vegetation) from sites with either intermittent or persistent winter snow cover to five different freeze‐thaw scenarios of realistic frequency and duration. Additionally, we set up a transplant experiment at our field site by reciprocally transplanting soil‐plant monoliths between sites with intermittent and persistent snow. Together, the field and laboratory experiments aimed to assess how carbon and nutrient leaching was affected by both historical snow conditions and short‐term (through freeze‐thaw scenarios and transplantation) changes in snow cover and thermal conditions.Both a greater number of freeze‐thaw cycles and longer duration of sub‐zero temperatures increased carbon and nutrient leaching from incubated soil cores. Cores from sites with persistent snow generally had lower nutrient losses under control conditions, but greater losses following induced freeze‐thaw cycles than cores from intermittent snow sites. The character of the leached dissolved organic carbon (DOC) suggested fresh organic material, such as live plant roots or microbes, as the source of carbon and nutrients. Nutrient losses from the plant‐soil systems in the field were greater at sites with persistent winter snow due to greater volumes of percolating water in spring. This suggests that increasingly severe and frequent soil freeze‐thaw events in oceanic mountain ecosystems can enhance the mobilization of C, N and P in labile forms but, in the absence of water fluxes, these nutrients would remain available for in‐situ cycling. Thus, under future warmer winter conditions, increased carbon and nutrient losses from oceanic mountain ecosystems could occur if winters with little snow coincide with wet spring conditions.

Stubble management effects on canola performance across different climatic regions of western Canada

Cardillo, M. J., Bullock, P., Gulden, R., Glenn, A. and Cutforth, H. 2015. Stubble management effects on canola performance across different climatic regions of western Canada. Can. J. Plant Sci. 95: 149–159. Previous research in the most arid region of the Canadian prairies has shown that wheat stubble cut tall the previous year can improve performance of the following canola crop. This study aimed to determine if tall stubble could benefit canola across the climatic conditions typically experienced in western Canada. Tall stubble impacts on canola were monitored over 11 site-years located throughout the prairies. At each site, tall stubble (50 cm) was compared with short stubble (20 cm). At some sites the stubble lodged allowing an unintended comparison between stubble that remained intact and stubble that was flattened. The comparison of snow water equivalent showed tall stubble caught more snow than short stubble but the benefit of additional spring soil moisture was masked by heavy spring precipitation in both 2011 and 2012. Canola biomass and yield were significantly lower in damaged versus intact stubble, either short or tall. In both years, wet spring conditions were followed by hotter and drier weather in the mid to late growing season. Soil under the damaged stubble (short or tall) likely warmed and dried more slowly in the spring, limiting early-season growth, biomass and yield. At sites where both tall and short stubble remained intact, there was a significant yield advantage with tall stubble. The intact tall stubble may have slowed evaporation and soil drying compared with intact short stubble, which reduced moisture stress later in the growing season, imparting a yield advantage.

Disentangling Fabiana imbricata (Solanaceae) regeneration: The importance of disturbance and rainfall

In Mediterranean ecosystems, fire influences plant population dynamics and changes plant community structure by affecting germination and establishment of seeder shrubs. Fabiana imbricata is a long-lived seeder shrub with a broad distribution in South America. In Northwestern Patagonia grasslands there are many records of F. imbricata recruitment after fires. We hypothesized that recruitment is promoted by: 1) soil erosion that exposes deeply buried seeds; 2) direct fire effects such as heat that could break seed dormancy; 3) indirect fire effects (i.e. increase of light availability and elimination of allelopathic substances) and 4) water availability in spring. In field conditions, we tested the effects of shading and soil disturbance on F. imbricata recruitment and seed availability and distribution in the soil profile. Under controlled conditions, we investigated the influence of leaf leachate, light, heat and water on seed germination and seedling emergence. Seed germination was inhibited by leachate, and seedling emergence was inhibited by seed heated to 80 °C and 120° for 5 min. F. imbricata seedlings only emerged in germination treatments that simulated wet and very wet spring conditions. Fire and postfire wind that favor seed exposure, combined with high precipitation early in the growing season, would be necessary for successful shrub recruitment. When F. imbricata shrubland colonizes the grassland, it strongly modifies local vegetation structure, reduces species richness and increases fuel loads. F. imbricata is a key species in the ecosystem specially related to fire regime. Information on the postfire regeneration of this species would provide valuable knowledge of the changes in biomass accumulation in a fire-prone Mediterranean ecosystem.

Understanding the effects of multiple sources of seasonality on the risk of pathogen spread to vineyards: vector pressure, natural infectivity, and host recovery

Seasonality plays an important role in the dynamics of infectious disease. For vector‐borne pathogens, the effects of seasonality may be manifested in the variability in vector abundance, vector infectiousness, and host‐infection dynamics over the year. The relative importance of multiple sources of seasonality on the spread of a plant pathogen, Xylella fastidiosa, into vineyards was explored. Observed seasonal population densities of the primary leafhopper vector, Graphocephala atropunctata, from 8 years of surveys in northern California were incorporated into a model of primary spread to estimate the risk of pathogen infection under different scenarios regarding seasonality in vector natural infectivity (i.e. constant or increasing over the season) and grapevine recovery from infection (i.e. none or seasonal recovery). The extent to which local climatic conditions affect risk estimates via differences in vector abundance was investigated. Seasonal natural infectivity, seasonal recovery, and especially the combination, reduced (up to 8‐fold on average) within‐season and cumulative yearly estimates of pathogen spread. Estimated risk of infection also differed greatly among years due to large differences in vector abundance, with wet and moderate winter and spring conditions favouring higher G. atropunctata abundance. Seasonal variation of the pathogen–vector interaction may play an important role in the dynamics of disease in vineyards, reducing the potential prevalence from what it could be in their absence. Moreover, climate, by affecting sharpshooter leafhopper abundance or activity, may influence Pierce’s disease dynamics.

Volatilização de amônia da ureia alterada por sistemas de preparo de solo e plantas de cobertura invernais no Centro-Sul do Paraná

O sistema plantio direto (PD) intensifica as perdas de N da ureia por volatilização, em comparação ao preparo convencional (PC). O objetivo deste estudo foi avaliar a magnitude desse efeito nas condições de temperatura amena e primavera chuvosa da região Centro-Sul do Paraná, bem como avaliar a influência de diferentes plantas de cobertura invernais (aveia-branca e ervilhaca comum) nas perdas de amônia (NH3) em PD. O estudo sobre o efeito dos preparos de solo foi realizado em experimento de longa duração (28 anos), e a avaliação das plantas de cobertura foi feita em experimento implantado especificamente com esse fim em área em PD por longo período (> 15 anos). Em ambos os experimentos cultivou-se milho. A ureia foi aplicada nas doses de 0, 80 e 160 kg ha-1 de N em apenas uma aplicação no experimento de preparos, e nas doses de 0, 100 e 200 kg ha-1 de N, divididas em duas aplicações, no experimento de plantas de cobertura. A volatilização de amônia foi avaliada durante 20 dias após a aplicação da ureia, utilizando coletores semiabertos estáticos. A atividade da urease no solo foi avaliada em ambos os experimentos. As maiores taxas de perda de NH3 ocorreram nos cinco dias que sucederam à aplicação de ureia. As perdas acumuladas atingiram 18 % da dose aplicada no PD e 3 % no PC, e as maiores perdas no PD podem ser parcialmente relacionadas à maior atividade da urease na camada superficial do solo. A volatilização de amônia não foi alterada pelo tipo de planta de cobertura. O parcelamento da adubação nitrogenada em cobertura por si só não garante a diminuição das perdas de N por volatilização, a qual é relacionada à ocorrência de chuva no período imediatamente posterior à aplicação da ureia.

Meteorological and Hydrological Influences on the Spatial and Temporal Prevalence of West Nile Virus in <I>Culex</I> Mosquitoes, Suffolk County, New York

The factors determining the spatial and temporal distribution of West Nile virus (family Flaviviridae, genus Flavivirus, WNV) activity are not well understood. Here, we explore the effects of hydrological and meteorological conditions on WNV infection among Culex genus mosquitoes collected during 2001-2009 in Suffolk County, Long Island, NY. We show that WNV infection rates in assayed pools of Culex mosquitoes are associated in both space and time with hydrological and meteorological variability. Specifically, wet winter, warm and wet spring conditions, and dry summer conditions are associated with the increased local prevalence of WNV among Culex mosquitoes during summer and fall. These findings indicate that within Suffolk County, and for a given year, areas at risk for heightened WNV activity may be identified in advance by using hydrology model estimates of land surface wetness and observed meteorological conditions.

Hydrologic Conditions Describe West Nile Virus Risk in Colorado

We examine the relationship between hydrologic variability and the incidence of human disease associated with West Nile virus (WNV; family Flaviviridae, genus Flavivirus) infection (hereafter termed “human WN cases”) in Colorado from 2002 to 2007. We find that local hydrologic conditions, as simulated by the Mosaic hydrology model, are associated with differences in human WN cases. In Colorado’s eastern plains, wetter spring conditions and drier summer conditions predict human WN cases. In Colorado’s western mountains, drier spring and summer conditions weakly predict human WN cases. These findings support two working hypotheses: (1) wet spring conditions increase the abundance of Culex tarsalis vectors in the plains, and (2) dry summer conditions, and respondent irrigational practices during such droughts, favor Cx. pipiens and Cx. tarsalis abundance throughout Colorado. Both of these processes potentially increase the local vector-to-host ratio, favoring WNV amplification among competent avian hosts and bridging to humans.

Frequency-dependent signals in multi-centennial oak vessel data

This work evaluates whether vessel size data contain a coherent spring precipitation signal over different frequency domains, and how this climatic information varies from the signal encoded in radial growth. The study was conducted at a forest site dominated by old oak trees ( Quercus petraea (Mattuschka) Liebl.) located in the southern part of the Swiss Alps. Measurements of earlywood vessel size of 27 cores from 12 oak trees were performed in order to build an unprecedented multi-centennial vessel size chronology. Age-independent long-term growth changes and climatic responses in the high-, mid- and low-frequency domains of differently composed chronologies are explored to test the stability of the signals. Results are compared with analyses of tree-ring width measurements from the same material to gain a deeper understanding of physiological processes. We find that mean vessel size data, in contrast to tree-ring width, carry a frequency-dependent signal. Although the signal of both parameters is similar in the low-frequency domain, the climate response in the high-frequency domain differs: vessel size responds negatively to wet spring conditions, whereas ring width mainly responds positively to water availability during the summer. We hypothesize that the processes responsible for signal registration in the specific frequencies are different. The differing high-frequency signals appear to be directly linked to dissimilar responses to weather conditions driving ring and vessel formation. In contrast, the long-term response is related to conditions that affect tree vigour and, due to a positive feedback on growth, is indirectly reflected in the vessels and ring width characteristics. Due to the change in the frequency related response observed in this pioneering study, it appears that the mean earlywood vessel size of oak is not an adequate proxy for long-term reconstruction of spring precipitation.

Soil properties and landscape factors affecting maize yield under wet spring conditions in eastern Canada

Spatial variation in soil properties is attributable in part to redistribution of moisture and topsoil and to soil compaction associated with water-logging. Digital Elevation Models (DEMs) can define topography at a fine scale where these processes may occur as related to field landscape positions such as footslope, depression, crest, and plateau. Our objective was to relate micro-relief (slope, elevation) to soil physical properties and to maize ( Zea mays L.) yield under wet spring conditions and delineate soil management units in the field. The experimental 9-ha field was located in the St-Lawrence Lowlands, Quebec, Canada. A topographical survey was conducted using an all-terrain vehicle (ATV) equipped with high-precision Global Positioning System (GPS) receivers sampling 3-D coordinates to generate a grid as fine as 3 m. The GPS sampling method was compared to a total station (TS) for land survey on a 20-m grid. Soil samples and grain yield were collected and geo-referenced on a 30-m grid. Kriging, mapping, and correlation analyses were conducted. Topographic data sampled using a GPS receiver embedded on an ATV were accurate (<10 cm) compared to TS. Soil compaction indexes (bulk density, clay and clay/OM ratio) were the most closely related to yield ( r 2 = −0.57 to −0.60). An independent dataset across the St-Lawrence Lowlands indicated that maize yield exceeding 10 t ha −1 in 1999 and 2000 was obtained with clay/OM ratios less than 12. The DEM and clay/OM ratio distribution maps were useful to locate five landscape positions of clay accumulation, water-logging, and soil compaction, forming two soil management units. In the footslope and depression management units, specific allocation of organic amendments may increase maize yield.