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41.
W. Van Der Werf R. Rabbinge W. Heijbroek 《European journal of plant pathology / European Foundation for Plant Pathology》1986,92(1):33-42
A simulation model was developed for the spring invasion of the beet cyst nematode,Heterodera schachtii Schmidt, into sugarbeet roots, according to the state variable approach. This model describes the processes of egghatch, emergence of second stage larvae from cysts, migration to roots and penetration into roots quantitatively, using published data.In 1983 a field experiment was conducted to test this model.H. schachtii cysts were introduced at depths 6–29 cm in PVC-cylinders, buried in the soil. The rooting depth of sugarbeet seedlings, growing in these cylinders, was limited to 5 cm by 50 m mesh nylon gauze. Every 10 days the second stage larvae, which had penetrated into the roots of these seedlings were counted. After 50 days, about 40% of the eggs had hatched. More than 20% of the emerged larvae penetrated if the cysts had been buried undeeply, and only 4% if the cysts had been buried at 29 cm depth.The model predicted the course of penetration into the root during the first 40 days with reasonable accuracy (r2=0.79), but in the 5th period of 10 days the model made an overestimation of more than 100%. Egghatch after 50 days was correctly simulated. The differences in penetration into the root between the model and the experiment might result from an oversimplified simulation of the penetration success or the neglection of mortality of second stage larvae. Detailed experiments should be done to provide better parameters for these factors.Samenvatting Volgens de toestandsvariabele-benadering werd een simulatiemodel ontwikkeld van de voorjaarspenetratie van het bietecystenaaltje. Het model beschrijft aan de hand van literatuurgegevens het uikomen van de eieren, het verlaten van de cyst door de larven, de migratie naar en de penetratie in de wortel.In 1983 werd een veldproef uitgevoerd om het model te toetsen. Cysten vanH. schachtii werden op 5 dieptes tussen 6 en 29 cm ingegraven in PVC-cylinders, welke waren verzonken in de bodem. De bewortelingsdiepte van de suikerbiete-zaailingen die hierin groeiden werd beperkt tot 5 cm door nylon gaas van 50 m maaswijdte. Elke 10 dagen werden de larven geteld die in de wortels van deze plantjes waren gepenetreerd. Na 50 dagen was 40% van de eieren uitgekomen. Meer dan 20% van de gelokte larven penetreerden als de cysten ondiep waren ingegraven, en slechts 4% als de cysten op 29 cm diepte waren ingegraven.Gedurende de eerste 40 dagen werd het verloop van de penetratie in de wortel met redelijke nauwkeurigheid door het model voorspeld (r2=0.79). In de 5e periode van 10 dagen maakte het model echter een overschatting van meer dan 100%. Het uitkomen van de eieren werd correct gesimuleerd. De verschillen in penetratie tussen het model en de proef zouden het gevolg kunnen zijn van een oververeenvoudigde simulatie van het penetratiesucces of van het verwaarlozen van de mortaliteit van de migrerende larven. Betere gegevens hierover zullen moeten komen uit detailproeven. 相似文献
42.
43.
A general bio-economic model for beef cattle production was used to define breeding objectives for Charolais cattle to be utilized in a variety of linked production systems. Economic weights were calculated for 16 traits (some with both direct and maternal components) in three production systems (pure-breeding and terminal crossing with beef or dairy cows) and two marketing strategies (sale or fattening of weaned surplus calves). Economic weights for the total breeding objective were calculated as weighted averages, where weights were numbers of cows expected to be mated with Charolais bulls in each production system and marketing strategy. Results suggest that the direct component of calving performance and cow longevity were of primary economic importance in all systems. Conception rate of cows and weaning weight reached about 50% of the standardized economic weight of calving performance in purebred systems with sale of weaned calves, whereas in purebred systems with fattening the economic importance of the direct component of cow conception rate, losses at calving, mature weight of cows, weaning weight, and fattening traits were of equal importance (each approximately about 20% that of calving performance). In terminal crossing systems, weaning weight was important when calves were sold at weaning, and fattening traits were important for systems selling fattened animals. The bio-economic model performed well under the conditions of this demonstration and could easily be customized for other applications. 相似文献
44.
旱地保护性耕作地表径流和土壤水分平衡模型 总被引:12,自引:3,他引:12
在田间试验和对现有径流模型及土壤水分平衡模型改进的基础上,建立了适用于保护性耕作的地表径流和土壤水分平衡模型。该模型以日为步长,根据气象数据、土壤水分状况、作物生长发育及耕作管理措施,模拟不同耕作管理体系下地表径流和田间水分平衡的变化。针对保护性耕作的特点,主要对径流曲线数字(USDA—Curve Number)法进行了改进,在PERFECT模型的基础上增加了坡度和降雨强度两因素的影响,从而使模型较全面地考虑了残茬覆盖、耕作、坡度及降雨强度等多种因素对径流的影响;采用简单实用的Priestley—Taylor公式计算潜在蒸散量,并考虑作物覆盖与残茬覆盖对土壤蒸发与作物蒸腾的影响。通过田间径流试验和根层有效贮水量测定数据的验证,证明了地表径流和土壤水分的模拟值与实测值比较接近。 相似文献
45.
宜吉共建黄河壶口瀑布旅游风景名胜区的合作方案研究 总被引:2,自引:0,他引:2
黄河壶口瀑布旅游风景名胜区由于地跨晋陕两省,长期以来以行政为单元进行独立开发的模式制约了景区的发展。本文在认真分析了现行的开发模式和三种可供选择的方案之后,提出了一种可行的创新方案。 相似文献
46.
关中平原小麦产量对气候变化区域响应的评价模型研究 总被引:4,自引:0,他引:4
根据关中地区宝鸡、西安、渭南与咸阳 4地 (市 )的 1 949~ 1 999年的逐年小麦单产记录序列以及 4地 (市 )的气象观测站点自建站以来至 2 0 0 0年近 5 0年的气象记录序列 ,对关中地区小麦产量与年均温、年降水作相关分析 ;探讨了关中地区小麦单产对气候变化区域响应的评价模型。结果发现 :关中平原气候具有暖干化趋势 ;随着气温变暖 ,小麦产量增加幅度减小 ;小麦产量对降水波动的响应比对气温波动的响应显著。 相似文献
47.
Assessing the potential impacts of alternative landscape designs on amphibian population dynamics 总被引:2,自引:1,他引:2
An individual-based, spatially explicit population model was used to predict the consequences of future land-use alternatives for populations of four amphibian species in two central Iowa (midwest USA) agricultural watersheds. The model included both breeding and upland habitat and incorporated effects of climatic variation and demographic stochasticity. Data requirements of the model include life history characteristics, dispersal behavior, habitat affinities, as well as land use and landcover in geographic information systems databases. Future scenarios were ranked according to change in breeder abundance, saturation, and distribution, compared to baseline conditions. Sensitivity of simulation results to changes in model parameters was also examined. Simulated results suggest that while all four species modeled are likely to persist under present and future scenario conditions, two may be more at risk from future landscape change. Although the study species are all widespread generalists regarded as having a low conservation priority, they depend on wetlands and ponds, increasingly endangered habitats in agricultural landscapes. Broader conservation strategies in the region would ensure that these currently common organisms do not become the endangered species of the future.This revised version was published online in May 2005 with corrections to the Cover Date. 相似文献
48.
Simulating evolution of glyphosate resistance in Lolium rigidum II: past, present and future glyphosate use in Australian cropping 总被引:1,自引:0,他引:1
Glyphosate is a key component of weed control strategies in Australia and worldwide. Despite widespread and frequent use, evolved resistance to glyphosate is rare. A herbicide resistance model, parameterized for Lolium rigidum has been used to perform a number of simulations to compare predicted rates of evolution of glyphosate resistance under past, present and projected future use strategies. In a 30‐year wheat, lupin, wheat, oilseed rape crop rotation with minimum tillage (100% shallow depth soil disturbance at sowing) and annual use of glyphosate pre‐sowing, L. rigidum control was sustainable with no predicted glyphosate resistance. When the crop establishment system was changed to annual no‐tillage (15% soil disturbance at sowing), glyphosate resistance was predicted in 90% of populations, with resistance becoming apparent after between 10 and 18 years when sowing was delayed. Resistance was predicted in 20% of populations after 25–30 years with early sowing. Risks of glyphosate resistance could be reduced by rotating between no‐tillage and minimum‐tillage establishment systems, or by rotating between glyphosate and paraquat for pre‐sowing weed control. The double knockdown strategy (sequential full rate applications of glyphosate and paraquat) reduced risks of glyphosate and paraquat resistance to <2%. Introduction of glyphosate‐resistant oilseed rape significantly increased predicted risks of glyphosate resistance in no‐tillage systems even when the double knockdown was practised. These increased risks could be offset by high crop sowing rates and weed seed collection at harvest. When no selective herbicides were available in wheat crops, the introduction of glyphosate‐resistant oilseed rape necessitated a return to a minimum‐tillage crop establishment system. 相似文献
49.
N. D. Paveley † J. M. Thomas T. B. Vaughan N. D. Havis D. R. Jones 《Plant pathology》2003,52(5):638-647
A function was derived to predict fungicide efficacy when more than one application of a single active ingredient is made to a crop, given parameters describing the dose–response curves of the component single-spray applications. In the function, a second application is considered to act on that proportion of the total pathogen population which was uncontrollable at the time of the first application (represented by the lower asymptote of the dose–response curve for the first treatment), plus any additional part of the population which survived the first application as a result of a finite dose being applied. Data to estimate the single-spray dose–response curve parameters and validate predictions of two-spray programme efficacy were obtained from separate subsets of treatments in four field experiments. A systemic fungicide spray was applied to wheat at a range of doses, at one or both of two times (t1 and t2), in all dose combinations. Observed values of the area under the disease progress curve (AUDPC) for septoria leaf blotch (Mycosphaerella graminicola) were used to construct response surfaces of dose at t1 by dose at t2 for each culm leaf layer. Parameters were estimated from single-spray and zero-dose treatment data only. The model predicted a high proportion (R2 = 71–95%) of the variation in efficacy of the two-spray programmes. AUDPC isobols showed that the dose required at t2 was inversely related to the dose at t1, but the slope of the relationship varied with the relative timings of t1 and t2 in relation to culm leaf emergence. Isobols were curved, so the effective dose – the total dose required to achieve a given level of disease suppression – was lower when administered as two applications. 相似文献
50.
A. van Maanen X.-M. Xu 《European journal of plant pathology / European Foundation for Plant Pathology》2003,109(7):669-682
An epidemic is the progress of disease in time and space. Each epidemic has a structure whose temporal dynamics and spatial patterns are jointly determined by the pathosystem characteristics and environmental conditions. One of the important objectives in epidemiology is to understand such spatio-temporal dynamics via mathematical and statistical modelling. In this paper, we outline common methodologies that are used to quantify and model spatio-temporal dynamics of plant diseases, with emphasis on developing temporal forecast models and on quantifying spatial patterns. Several examples of epidemiological models in cereal crops are described, including one for Fusarium head blight. 相似文献