土壤阻力连续测试系统农田试验研究

土壤阻力连续测试系统可连续获取农田压实的土壤阻力信息。为研究土壤阻力连续测试系统测试土壤阻力指数(TRI)的适用性,安排了小区对比、大田对比和工作速度影响3个试验,进行了土壤阻力指数TRI值与土壤圆锥指数CI值对比分析。试验结果表明:在表征农田土壤压实程度上,TRI值与CI值具有一致性,即利用土壤阻力连续测量系统测取的TRI数据可以反应农田土壤的压实程度;土壤阻力连续测量系统采样连续、数据信息量大和采样效率高,适合于大面积农田土壤信息快速采集,有利于变耕深耕作技术的开展;在保证系统高效、安全和测试数据稳定的前提下,试验结果显示测试系统较理想的工作速度是1.0m/s。     

Response of alluvial fan systems to the late Pleistocene to Holocene climatic transition: contrasts between the margins of pluvial Lakes Lahontan and Mojave, Nevada and California, USA

Dated shorelines of late Pleistocene pluvial Lakes Lahontan (Great Basin Desert, northwest Nevada) and Mojave (Mojave Desert, eastern California) provide timelines for the assessment of alluvial fan sedimentation at the lake margins during the late Pleistocene to early Holocene. Two sets of alluvial fan systems have been mapped: the Stillwater fans, feeding Lake Lahontan; and the Zzyzx fans, feeding Lake Mojave. Their contrasting morphologies suggest different responses of the two fan systems to late Pleistocene to early Holocene climatic change. At the time the Stillwater fan systems underwent minimal sedimentation, with the catchment hillslopes apparently stable. The Zzyzx fans experienced major changes in water and sediment supply from the catchment hillslopes. There was a major phase of hillslope debris-flow activity, followed by fanhead trenching and distal fan progradation. Both areas were wetter and colder in the late Pleistocene than they are today, but during the transition to the Holocene the Zzyzx area was more likely to experience intense rains associated with the monsoonal penetration of warm moist tropical air into the Southwest. Vegetation reconstructions for the late Pleistocene to the early Holocene suggest that catchment hillslopes in the Mojave supported a desert shrub vegetation, but those in the Stillwaters supported juniper woodland and grasses at low elevations and pine at higher elevations. Contrasts in hillslope vegetation cover together with storm activity may account for the different responses of the alluvial fans to climatic change during the Pleistocene to Holocene climatic transition. After the falls in lake levels of Lakes Lahontan and Mojave in the early Holocene, both areas underwent aridification, resulting in reductions in hillslope vegetation cover. Increased storm runoff led to fanhead trenching and distal progradation of the alluvial fans. Variations in fan style at that time may relate primarily to base-level conditions resulting from different gradients on the exposed lake shores.     

Products from the sensitised photo-oxidation of 2-dimethylamino-5,6-dimethylpyrimidin-4-ol

The products from the methylene blue sensitised photo-oxidation of 2-dimethylamino-5,6-dimethylpyrimidin-4-ol (I) in deuterochloroform/deuteroacetone have been investigated. A zwitterion and a hydroperoxide are formed initially, with the zwitterion predominating. The zwitterion compound degrades or reacts in the solid state on silica gel to give further products.     

Vapour pressure of permethrin

The vapour pressures of the separate isomers of permethrin have been determined over a range of temperatures by two laboratories using different versions of the gas saturation method. A statistical analysis of the sets of data from the two laboratories shows no significant differences for the cis isomers but a small difference in the 20°C extrapolated values for the trans isomer exists. However, this difference is discounted as arising from experimental error and the mean values of the estimated vapour pressures at 20°C are given as 2.5 μPa (cis) and 1.5 μPa (trans).     

Variance estimation for population attributable risk in a complex cross-sectional animal health survey

Population attributable risk estimates offer a method of combining information on population exposure and disease risk factors into a single measure. Univariate and multivariable methods exist for calculating point estimates and variances under the assumption of equal sampling probabilities. National Animal Health Monitoring System national studies typically use a complex survey design (where selection probabilities vary by design strata), which makes use of these methods of calculating variance inappropriate. We suggest the use of a method called "delete-a-group" jackknife to estimate the variance of population attributable risk when a complex survey design has been implemented. We demonstrate the method using an example of Johne's disease. Advantages of the "delete-a-group" jackknife method include simplicity of implementation and flexibility to estimate variance for any point estimate of interest.     

Kinetic and thermodynaimic aspects of the dye-sensitised photo-oxidation of bioresmethrin and related compounds

The Rose Bengal sensitised photo-oxidation of bioresmethrin (I), 2-benzylfuran-4-ylmethyl acetate (II), and 2-benzylfuran-4-ylmethanol (III) has been studied in methanol and methanol + water (1 + 1 by volume) solutions by monitoring the rate or oxygen removal from the system. The results indicate that the compounds studied are oxidised via reaction with singlet oxygen. Values for the rate constants for reaction of singlet oxygen with compounds I-III have been determined over the temperature range 293–308 K, and the energy of activation and entropy of activation for the reactions have been determined. The data have been interpreted in terms of the site of attack of singlet oxygen on the compounds.     

A comparison of the shell strength of eggs from battery and deep‐litter units

The investigation involved 966 light‐hybrid pullets, 366 accommodated in battery cages and 600 kept on deep litter. Samples of their eggs were taken at four stages during the laying year for measurement of shell strength by the deformation technique. The results of these measurements were very similar for eggs produced under the two systems of housing.     

Evaluation of bacteriologic culture of individual and pooled fecal samples for detection of Mycobacterium paratuberculosis in dairy cattle herds

OBJECTIVES: To determine the sensitivity of bacteriologic culture of pooled fecal samples in detecting Mycobacterium paratuberculosis, compared with bacteriologic culture of individual fecal samples in dairy cattle herds. STUDY DESIGN: Cross-sectional study. ANIMALS: 24 dairy cattle herds. PROCEDURE: Individual and pooled fecal samples were submitted for bacteriologic culture, and results were compared between these groups. RESULTS: Ninety-four and 88% of pooled fecal samples that contained feces from at least 1 animal with high (mean, > or = 50 colonies/tube) and moderate (mean, 10 to 49 colonies/tube) concentrations of M paratuberculosis, respectively, were identified by use of bacteriologic culture of pooled fecal samples. Prevalences of paratuberculosis determined by bacteriologic culture of pooled and individual fecal samples were highly correlated. CONCLUSIONS AND CLINICAL RELEVANCE: Bacteriologic culture of pooled fecal samples provided a valid and cost-effective method for the detection of M paratuberculosis infection in dairy cattle herds and can be used to estimate prevalence of infection within a herd.     

Association between bovine-leukosis virus seroprevalence and herd-level productivity on US dairy farms

Bovine-leukosis virus (BLV; also termed ‘bovine-leukemia virus’) is a retrovirus that primarily affects lymphoid tissue of dairy and beef cattle. Our objective was to investigate the association between BLV infection and annual value of production (AVP) on dairy herds within the United States, as part of the USDA National Animal Health Monitoring System’s 1996 dairy study. 1006 herds (in 20 states) with at least 30 dairy cows were interviewed during 1996. The agar-gel immunodiffusion test was used to detect serum antibodies to BLV. 10–40 cows from each herd were tested and each tested cow was classified as negative or positive based on results of a single test.

A multivariable regression model was used with the 976 herds with complete data for analysis. When compared to herds with no test-positive cows, herds with test-positive cows produced 218 kg per cow (i.e. 3%) less milk. The average reduction in AVP was $ 59 per cow for test-positive herds relative to test-negative herds. For the dairy industry as a whole, BLV seropositivity was associated with loss to producers of $ 285 million and $ 240 million for consumers. Most of this $ 525 million industry loss was due to reduced milk production in test-positive herds.     

Evaluation of herd sampling for Salmonella isolation on midwest and northeast US dairy farms

Epidemiologic investigations of Salmonella infections in dairy cattle often rely on testing fecal samples from individual animals or samples from other farm sources to determine herd infection status. The objectives of this project were to evaluate the effect of sampling frequency on Salmonella isolation and to compare Salmonella isolation and serogroup classification among sample sources on 12 US dairy farms sampled weekly for 7-8 weeks. Three herds per state were enrolled from Michigan, Minnesota, New York and Wisconsin based upon predefined herd-size criteria. Weekly samples were obtained from cattle, bulk tank milk, milk filters, water and feed sources and environmental sites. Samples were submitted to a central laboratory for isolation of Salmonella using standard laboratory procedures. The herd average number of cattle fecal samples collected ranged from 26 to 58 per week. Salmonella was isolated from 9.3% of 4049 fecal samples collected from cattle and 12.9% of 811 samples from other sources. Serogroup C1 was found in more than half of the samples and multiple serogroups were identified among isolates from the same samples and farms. The percentage of herd visits with at least one Salmonella isolate from cattle fecal samples increased with overall herd prevalence of fecal shedding. Only the three herds with an average fecal shedding prevalence of more than 15% had over 85% of weekly visits with at least one positive fecal sample. The prevalence of fecal shedding from different groups of cattle varied widely among herds showing that herds with infected cattle may be classified incorrectly if only one age group is tested. Testing environmental sample sources was more efficient for identifying infected premises than using individual cattle fecal samples.