Predicting the risk of soybean rust in Minnesota based on an integrated atmospheric model.

To minimize crop loss by assisting in timely disease management and reducing fungicide use, an integrated atmospheric model was developed and tested for predicting the risk of occurrence of soybean rust in Minnesota. The model includes a long-range atmospheric spore transport and deposition module coupled to a leaf wetness module. The latter is required for spore germination and infection. Predictions are made on a daily basis for up to 7 days in advance using forecast data from the United States National Weather Service. Complementing the transport and leaf wetness modules, bulk (wet plus dry) atmospheric deposition samples from Minnesota were examined for soybean rust spores using a specific DNA test and sequence analysis. Overall, the risk prediction worked satisfactorily within the bounds of the uncertainty associated with the use of modeled 7-day weather forecasts, with more than 65% agreement between the model forecast and the DNA test results. The daily predictions are available as an advisory to the user community through the University of Minnesota Extension. However, users must take the actual decision to implement the disease management strategy.

Levels and source apportionment of volatile organic compounds in southwestern area of Mexico City.

Thirteen volatile organic compounds (VOCs) were quantified at three sites in southwestern Mexico City from July 2000 to February 2001. High concentrations of different VOCs were found at a Gasoline refueling station (GS), a Condominium area (CA), and at the University Center for Atmospheric Sciences (CAS). The most abundant VOCs at CA and CAS were propane, n-butane, toluene, acetylene and pentane. In comparison, at GS the most abundant were toluene, pentane, propane, n-butane, and acetylene. Benzene, a known carcinogenic compound had average levels of 28, 35 and 250ppbC at CAS, CA, and GS respectively. The main contributing sources of the measured VOCs at CA and CAS were the handling and management of LP (Liquid Propane) gas, vehicle exhaust, asphalt works, and use of solvents. At GS almost all of the VOCs came from vehicle exhaust and fuel evaporation, although components of LP gas were also present. Based on the overall results possible abatement strategies are discussed.

The ozone component of global change: potential effects on agricultural and horticultural plant yield, product quality and interactions with invasive species.

The productivity, product quality and competitive ability of important agricultural and horticultural plants in many regions of the world may be adversely affected by current and anticipated concentrations of ground-level ozone (O3). Exposure to elevated O3 typically results in suppressed photosynthesis, accelerated senescence, decreased growth and lower yields. Various approaches used to evaluate O3 effects generally concur that current yield losses range from 5% to 15% among sensitive plants. There is, however, considerable genetic variability in plant responses to O3. To illustrate this, we show that ambient O3 concentrations in the eastern United States cause substantially different levels of damage to otherwise similar snap bean cultivars. Largely undesirable effects of O3 can also occur in seed and fruit chemistry as well as in forage nutritive value, with consequences for animal production. Ozone may alter herbicide efficacy and foster establishment of some invasive species. We conclude that current and projected levels of O3 in many regions worldwide are toxic to sensitive plants of agricultural and horticultural significance. Plant breeding that incorporates O3 sensitivity into selection strategies will be increasingly necessary to achieve sustainable production with changing atmospheric composition, while reductions in O3 precursor emissions will likely benefit world food production and reduce atmospheric concentrations of an important greenhouse gas.

Uncertainties in the current knowledge of some atmospheric trace gases associated with U.S. agriculture: a review.

Approximately 80 different crop species are grown in the United States in widely differing geographic areas, climatic and edaphic conditions, and management practices. Although the majority of cultivated acreage in the United States is planted with only about 10 primary crops, uncertainties associated with trace gas emissions arise from: (1) limited data availability, (2) inaccurate estimates because of large temporal and spatial variability in trace gas composition and magnitude of trace gas emissions from agricultural activities, (3) differing characteristics of pollutant emissions from highly dispersed animal feed-lots, and (4) limited understanding of the emissions of semi-volatile organic compounds (SVOCs) associated with agriculture. Although emission issues are of concern, so also is atmospheric deposition to cropping systems, including wet and dry nitrogen, minerals, and organic compounds. These can have feedback effects on trace gas emissions. Overall, the many gaps in our understanding of these aspects of agricultural systems deserve serious attention.

Introduction of Asian Soybean Rust Urediniospores into the Midwestern United States-A Case Study.

In 2005, weekly rain samples collected at 124 National Atmospheric Deposition Program/National Trends Network (NADP/NTN) sites in the eastern and central United States were screened for Asian soybean rust (ASR; Phakopsora pachyrhizi) urediniospores. Application of a quantitative polymerase chain reaction method detected P. pachyrhizi DNA in the filter residue of rain samples collected during the week of 19 to 26 July 2005 in Minnesota, Missouri, and South Dakota. To determine the geographic origin of ASR urediniospores in those weekly composite samples, back air trajectories of the lifted condensation and mixed boundary layers were calculated for each rain event within the week, by sampling site. The calculations, based on the hybrid single-particle lagrangian integrated trajectory model, pointed to source areas in eastern and southern Texas. In a separate case, DNA of P. pachyrhizi was detected in a 28 June to 5 July 2005 rain sample from an eastern Texas site. Back trajectories pointed to southern Texas and the Yucatan Peninsula in Mexico as potential source areas of ASR urediniospores. Vertical motions of those back trajectories indicated a ventilation of the boundary layer in the upwind areas, suggesting the possible injection of urediniospores into the free troposphere where they can be transported for long distances before wet deposition.

Atmosphere and agriculture in the new millennium.

Effects of changing climate (CO(2), O(3), aerosols, UV-B radiation, temperature and precipitation) on crops are predominantly based on univariate studies. Limited bivariate studies suggest rising CO(2) levels would be beneficial to crops but may be offset by adverse O(3) effects. Elevated UV-B and ambient crop yields are difficult to project due also to limited research. Climate warming concerns, using average daily temperatures may be less important than the effects of rising nocturnal temperatures on crop growth. Traditional approaches of examining air pollutant-induced visible foliar injury or the effects of single air pollutants on crop productivity need to be redirected to the analysis of integrated holistic systems. In that context, present and future agriculture in India and the USA are compared.

Joint effects of elevated levels of ultraviolet-B radiation, carbon dioxide and ozone on plants.

There is growing interest regarding the joint effects of elevated levels of surface ultraviolet B (UV-B) radiation, carbon dioxide (CO2) and ozone (O3) on plants. Our current knowledge of this subject is too limited to draw any specific conclusions, although one might state that such effects are likely to be highly species dependent and may be more than additive, additive or less than additive. There are a number of uncertainties associated with the experimental protocols used and the conclusions reached in many studies. Nevertheless, in North America, there appear to be genotypes of three monocot crop species (Avena sativa L., Oryza sativa L. and Sorghum vulgare L.); six dicot crops (Cucumis sativus L., Lactuca sativa L., Lycopersicon esculentum Mill., Phaseolus vulgaris L., Pisum sativum L. and Solanum tuberosum L.) and two conifer species (Pinus ponderosa Dougl. and Pinus taeda L.) that may be considered sensitive to the joint effects of elevated levels of UV-B, CO2 and O3. However, to provide a more reliable assessment or validation of the predictions, future research must consider the concept of plant response surfaces and describe them more fully in numerical terms. Achieving that objective will require close cooperation among a number of scientists representing geographic locations with known spatial and temporal differences in UV-B, CO2 and O3 to conduct experiments under their site-specific conditions, using common plant materials and experimental protocols.

Sampling and physico-chemical analysis of precipitation: a review.

Wet deposition is one of two processes governing the transfer of beneficial and toxic chemicals from the atmosphere on to surfaces. Since the early 1970s, numerous investigators have sampled and analyzed precipitation for their chemical constituents, in the context of "acidic rain" and related atmospheric processes. Since then, significant advances have been made in our understanding of how to sample rain, cloud and fog water to preserve their physico-chemical integrity prior to analyses. Since the 1970s large-scale precipitation sampling networks have been in operation to broadly address regional and multi-regional issues. However, in examining the results from such efforts at a site-specific level, concerns have been raised about the accuracy and precision of the information gathered. There is mounting evidence to demonstrate the instability of precipitation samples (e.g. with N species) that have been subjected to prolonged ambient or field conditions. At the present time precipitation sampling procedures allow unrefrigerated or refrigerated collection of wet deposition from individual events, sequential fractions within events, in situ continuous chemical analyses in the field and even sampling of single or individual rain, cloud and fog droplets. Similarly analytical procedures of precipitation composition have advanced from time-consuming methods to rapid and simultaneous analyses of major anions and cations, from bulk samples to single droplets. For example, analytical techniques have evolved from colorimetry to ion chromatography to capillary electrophoresis. Overall, these advances allow a better understanding of heterogeneous reactions and atmospheric pollutant scavenging processes by precipitation. In addition, from an environmental perspective, these advances allow better quantification of semi-labile (e.g. NH4+, frequently its deposition values are underestimated) or labile species [e.g. S (IV)] in precipitation and measurements of toxic chemicals such as Hg and PCBs (polychlorinated biphenyls). Similarly, methods now exist for source-receptor studies, using for example, the characterization of reduced elemental states and/or the use of stable isotopes in precipitation as tracers. Future studies on the relationship between atmospheric deposition and environmental impacts must exploit these advances. This review provides a comprehensive and comparative treatment of the state of the art sampling methods of precipitation and its physico-chemical analysis.

An integrative analysis of the role of atmospheric deposition and land management practices on nitrogen in the US agricultural sector.

Additions of anthropogenic nitrogen (N) compounds constitute one of the major classes of air pollutants of significance to human health and the environment. Reliance on wet deposition measurements alone can lead to considerable underestimates (by 40-60%) of the total (wet + dry) atmospheric N deposition. In addition, wet deposition of N are about 20% of the levels that are lost due to volatilization (primarily ammonia). Nevertheless, in the agricultural sectors of the Mississippi River basins, farm management practices, and recycling of N within cropping systems clearly outweigh the contributions of atmospheric deposition. As opposed to native vegetation and forests, there are no records of the negative effects of atmospheric N deposition on crop yield. Similarly, field studies on the interactions of atmospheric N compounds with the incidence and spread of pathogens does not permit any generalizations. Nitrogen applied as fertilizer affects disease probably more by its effect on the plant growth than by its effects on pathogens. In contrast, atmospheric nitrogen dioxide appears to be a stimulant of aphid performance. Under conditions of heavy weed infestation, N fertilization stimulates weed growth and competitiveness, rather than crop yield.