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Summer cover crop impacts on soil percolation and nitrogen leaching from a winter corn field 总被引:1,自引:0,他引:1
The impacts of a leguminous summer cover crop (sunn hemp; Crotalaria juncea) on nitrogen leaching from a corn (Zea mays L.) field was evaluated by direct measurements of soil water content and nitrogen balance components, complemented by direct and inverse modeling as an exploratory tool to better understand water flow and nitrogen balances in the soil. Water and nitrogen inputs and outputs were measured during winter corn production in an experimental field located in the south Miami-Dade basin in southern Florida (USA). Data from the last two seasons (2001-2002 and 2002-2003) of a 4-year study are presented. The field was divided into six 0.13 ha plots. One-half of the plots were rotated with sunn hemp (CC plots) during the summer while the remaining plots were kept fallow (NC plots). Sweet corn management was uniform on all plots and followed grower recommended practices. A numerical model (WAVE) for describing water and agrochemical movement in the soil was used to simulate water and nitrogen balances in both types of plots during the corn seasons. The hydrodynamic component of WAVE was calibrated with soil water data collected continuously at three depths, which resulted in accurate soil water content predictions (coefficients of efficiency of 0.85 and 0.91 for CC and NC plots, respectively). Measured components of the nitrogen balance (corn yields, estimated nitrogen uptake, and soil organic nitrogen) were used to positively assess the quality of the nitrogen simulation results. Results of the modeled water balance indicate that using sunn hemp as a cover crop improved the soil physical conditions (increase in soil water retention) and subsequently enhanced actual crop evapotranspiration and reduced soil drainage. However, nitrogen simulation results suggest that, although corn nitrogen uptake and yields were slightly higher in the CC plots than in the NC plots, there were net increases of soil N content that resulted in increased N leaching to the shallow aquifer. Therefore, the use of sunn hemp as cover crop should be coupled with reductions in N fertilizer applied to the winter crop to account for the net increase in soil N content. 相似文献
34.
D. E. te Beest M. W. Shaw S. Pietravalle F. van den Bosch 《European journal of plant pathology / European Foundation for Plant Pathology》2009,124(3):413-425
Disease–weather relationships influencing Septoria leaf blotch (SLB) preceding growth stage (GS) 31 were identified using
data from 12 sites in the UK covering 8 years. Based on these relationships, an early-warning predictive model for SLB on
winter wheat was formulated to predict the occurrence of a damaging epidemic (defined as disease severity of 5% or > 5% on
the top three leaf layers). The final model was based on accumulated rain > 3 mm in the 80-day period preceding GS 31 (roughly
from early-February to the end of April) and accumulated minimum temperature with a 0°C base in the 50-day period starting
from 120 days preceding GS 31 (approximately January and February). The model was validated on an independent data set on
which the prediction accuracy was influenced by cultivar resistance. Over all observations, the model had a true positive
proportion of 0.61, a true negative proportion of 0.73, a sensitivity of 0.83, and a specificity of 0.18. True negative proportion
increased to 0.85 for resistant cultivars and decreased to 0.50 for susceptible cultivars. Potential fungicide savings are
most likely to be made with resistant cultivars, but such benefits would need to be identified with an in-depth evaluation. 相似文献
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ABSTRACT Most models for the spread of fungicide resistance in plant pathogens are focused on within-field dynamics, yet regional invasion depends upon the interactions between field populations. Here, we use a spatially implicit metapopulation model to describe the dynamics of regional spread, in which subpopulations correspond to single fields. We show that the criterion for the regional invasion of pathogens between fields differs from that for invasion within fields. That is, the ability of a fungicide-resistant strain of a pathogen to invade a field population does not necessarily imply an ability to spread through many fields at the regional scale. This depends upon an interaction between the fraction of fields that is sprayed and the reproductive capacity of the pathogen. This result is of practical significance and indicates that resistance management strategies which currently target within-field processes, such as the use of mixtures and alternations of fungicides, may be more effective if between-field processes also were targeted; for example, through the restricted deployment of fungicides over large areas. We also show that the fraction of disease-free fields is maximized when the proportion of fields that is sprayed is just below the threshold for invasion of the resistant strain. 相似文献
36.
Nielsen R van den Bosch JF Plambeck T Sørensen V Nielsen JP 《Veterinary microbiology》2000,71(1-2):81-87
The reference strains of the 12 serotypes of Actinobacillus pleuropneumoniae express one or two of three different RTX exotoxins designated Apx I, Apx II and Apx III. The toxins are important virulence factors. In the present study, ELISAs with purified Apx I, Apx II and Apx III, respectively, as antigen were evaluated as candidates for serological diagnosis of Actinobacillus pleuropneumoniae infection in pigs. The pigs were inoculated with biotype 1, serotypes 1-12, and biotype 2, serotype 14, respectively. A strong humoral antibody response was seen to all the three antigens in most pigs irrespective of the serotype used for inoculation. However, titers to the exotoxins secreted by the serotype used for inoculation were generally highest. The results show that toxin proteins of Actinobacillus pleuropneumoniae are antigenically related and that a correlation between serotype and secretion of exotoxin is not revealed serologically in the ELISA test. 相似文献
37.
F. G. J. M. van den Bosch 《Euphytica》1987,36(3):783-790
Summary When mungbean landraces from East Java were intercropped with maize, genetic variation for grain yield was observed. Three cycles of selection resulted in a yield increase of 24% as compared to the original landraces. The yield of the maize component in the mixture was not affected by the increase of the mungbean yield. 相似文献
38.
Hesterberg UW Bagnall R Perrett K Bosch B Horner R Gummow B 《Journal of the South African Veterinary Association》2008,79(1):15-18
A serological survey of Brucella abortus in cattle originating from communal grazing areas of Kwa Zulu Natal was carried out between March 2001 and December 2003. The survey was designed as a 2-stage survey, considering the diptank as the primary sampling unit. In total 46 025 animals from 446 diptanks of 33 magisterial districts were sampled and tested using the Rose Bengal test and Complement Fixation Test. The apparent prevalence at district level was adjusted for clustering, diagnostic test sensitivity and specificity, and mapped using ArcView version 3.3. The prevalence of brucellosis in communal grazing areas of Kwa-Zulu Natal was found to be 1.45 % (0.84-2.21%) and varied from 0 to 15.6 % between magisterial districts. In 19 of the 33 magisterial districts no serological reactors were observed. A large variation in prevalence was found within diptank areas. Brucellosis was found to be most prevalent in the northeastern area of the province. The findings of the survey are discussed. 相似文献
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Acute polyneuromyopathy with respiratory failure secondary to monensin intoxication in a dog
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Luis Bosch LV MSc Alexa M. Bersenas DVM MSc DACVECC Shane Bateman DVM DVSc DACVECC 《Journal of Veterinary Emergency and Critical Care》2018,28(1):62-68