共查询到20条相似文献，搜索用时 31 毫秒
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Evaluation of sampling methods and assessment of the sample size to estimate the weed seedbank in soil, taking into account spatial variability 总被引：1，自引：0，他引：1
As field sampling is time consuming, it is necessary to develop efficient sampling techniques to obtain accurate estimates of the weed seedbank in soil. The relative efficiency between sampling schemes depends on the spatial variability in weed seed density across agricultural fields. Spatial variability of the weed seed density was characterized by theoretical correlograms. A systematic sampling (square grill) scheme was considered and it was found that, taking into account spatial variability, this sampling scheme was more efficient than simple random sampling. As a result, the sample size can be reduced in comparison with that given in previous studies, where spatial correlation was ignored. The reduction depends on the correlation structure defined as a function of the ratio, τ, between the nugget effect and the sill of the variogram. The maximum reduction of the sample size, without loss of either precision or confidence level corresponds to the case where there is no nugget effect, τ = 0. The opposite extreme case, where the reduction is nil, corresponds to the case of a pure nugget effect τ = 1. The abaci based on given expressions are provided to determine the sample size in species whose spatial pattern can be fitted either to a Poisson or to a negative binomial distribution. 相似文献
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S. A. Ward R. Rabbinge W. P. Mantel 《European journal of plant pathology / European Foundation for Plant Pathology》1985,91(2):93-99
In attempts to reduce the time required for monitoring cereal aphid populations, it has been suggested that direct counting be replaced by the use of incidence counts: estimation of aphid density from the proportion of wheat tillers infested. It is important, however, that the use of this simpler and more rapid method does not result in a loss of accuracy. This paper calculates the minimum sample size (number of tillers to be inspected) required to yield a given accuracy, using the two alternative sampling methods. Over the range of aphid densities close to the economic thresholds for pesticide application, the use of incidence counts does not require a much greater sample size than that needed for direct counting.Samenvatting Teneinde de bemonsteringstijd voor graanluizen te reduceren en een eenvoudige betrouwbare bemonsteringsmethode te ontwikkelen wordt telling van het aantal individuen per halm vaak vervangen door bepaling van het bezettingspercetage. Deze eenvoudige methode mag evenwel niet leiden tot een onaanvaardbaar verlies in nauwkeurigheid. Daarom wordt voor de directe telmethode en de methode met infectiepercentages de minimale monstergrootte bepaald bij een van te voren vastgestelde nauwkeurigheid. Het blijkt dat bij bladluizendichtheden, die dicht bij de economische schadedrempel liggen, de monsters bij de twee methoden niet in groote behoeven te verschillen. 相似文献
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A. G. Carson 《国际虫害防治杂志》2013,59(4):420-424
Abstract In field experiments conducted at the Nyankpala Agricultural Station, Ghana, during 1976–77, soil moisture conditions appeared to be the deciding factor in determining the frequency of handweeding needed to obtain maximum seed cotton yields. In 1976, when planting was early and the late, heavy rains in October prolonged weed growth, two handweedings at 4 and 8 weeks after seeding (w.a.s.) gave comparable yields to continuous weeding and significantly better yields than an alachlor + fluometuron herbicide mixture. Supplementary weeding did not enhance the mixture's performance. In 1977, planting was relatively late and in the peak of the rainy season and so late weed growth was reduced. A single handweeding at 4 w.a.s. gave as good a yield as repeated handweeding treatments under these conditions. The alachlor + fluometuron mixture also gave adequate weed control and again supplementary weeding did not improve it significantly. In herbicide evaluation experiments, the safety and performance of pendimethalin and dinitramine herbicides were much influenced by the rainfall pattern immediately following application. With a relatively drier period following application in 1976, the higher rate of these herbicides depressed yields. This rate produced optimum yields in 1977, however, when a very wet period followed application. Prodiamine and the alachlor + fluometuron mixture were the herbicides least affected by soil moisture and they consistently produced good yields. 相似文献
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荔枝龟背天牛幼虫空间分布型研究 总被引：3，自引：0，他引：3
对荔龟背天牛幼虫于荔枝园中的空间分状况调查和分析，表明该虫的空间分布为负二项分布；空间图式是聚集型；分布的基本成分为疏松的个体群。聚集行为受环境因素（主要是荔枝品种）的影响，此外，利用分布型参数确定了龟背天牛的理论抽样数并建立了序贯抽样检定表。 相似文献
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S. A. Ward R. Rabbinge W. P. Mantel 《European journal of plant pathology / European Foundation for Plant Pathology》1985,91(2):100-104
Two approaches have been used in the monitoring of local populations of cereal aphids: direct counting of aphids on a number of tillers, and the less time-consuming assessment of incidence levels (the proportion of tillers infested). This paper compares the accuracy of these two methods, using a fixed sample size, as is desirable in a practical monitoring system. It is shown that the two methods are equally reliable over a range of incidence levels, but that the confidence intervals for the population density are very broad. Reduction of these sampling error requires a considerable increase in sample size, so they should instead be taken into account in the management decision-making process.Samenvatting Er worden doorgaans twee methoden gebruikt om de dichtheid van graanluizen vast te stellen: directe telling en bepaling van het bezettingsperentage. De nauwkeurigheid van deze twee methoden wordt hier vergeleken bij een constante monstergrootte, die gewenst is bij praktische waarnemingssystemen. De beide methoden zijn even betrouwbaar over een reeks van bezettingspercentages, maar de betrouwbaarheids-intervallen zijn erg ruim. Verkleining van deze bemonsteringsfouten vereist een aanzienlijke toename van de monstergrootte, zodat het waarschijnlijk beter is deze fouten in het beslissingsproces voor de bestrijding te betrekken. 相似文献
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不同取样尺度农田土壤速效养分空间变异特征初步研究 总被引：14，自引：1，他引：13
以3种取样间距(100m、50m、25m)进行网格取样,对土壤速效养分的空间变异性进行研究。结果表明:取样间距对土壤速效养分的含量水平、变异系数影响不显著;取样间距对合理取样数目具有一定的影响,合理取样数目分别为:碱解氮(71)、速效磷(36)、速效钾(18)。土壤速效养分的空间变异性主要受结构因素影响,但碱解氮与速效磷受随机因素影响强于速效钾。利用Kriging内插法绘制了不同取样间距土壤速效养分的等值线图。 相似文献
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Densities of aphids (Aphis gossypii and A. spiraecola) and mummified aphids at different phenological stages of a blueberry crop were estimated for the purpose of developing sampling plans. Our data set comprised 99 samples taken during the period 2006–2008 in four fields in Buenos Aires Province, Argentina. Estimation of population density based on the proportion of sample units infested by individuals was investigated. We also calculated the minimum number of sample units to estimate the density of individuals on buds and buds + flowers using enumerative sampling. The relative precision of both methods was compared. Moreover, an enumerative sequential sampling protocol was developed. The presence–absence sampling plan gave density estimates with large variances (as measured by confidence intervals and large standard errors). The aggregation of mummies was similar on buds and buds + flowers, so the required number of sample units for density estimates was the same. Relative precision of estimates was much lower for the presence–absence sampling than the enumerative sampling, even at intermediate densities. An enumerative sequential plan would be the most appropriate and useful method in management plans for aphids and mummified aphids in blueberries. 相似文献
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通过调查研究，建立了香蕉园和粉蕉园节肢动物类群物种数与抽样数的关系模型，给出了进行物种数调查时最佳抽样数为31株，不同抽样方式调查的节肢动物类群物种类的比较结果表明除单行聚样外的各种取样方式均可采用。 相似文献
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县域土壤养分离群样点检测及其合理采样数研究 总被引：6，自引：0，他引：6
为进一步研究县域耕地土壤养分质量评价,增加采样数据的准确性和减少采样分析成本,本试验以白水县为研究区域,对2226个采样点的土壤样品中有效磷、碱解氮和速效钾采用四分位数法和局部Moran’s I方法进行全局和局部离群样点的去除,并对去除后的采样点进行空间特征分析。然后采用经典统计学(Cochran公式)方法和地统计学(普通克里金)方法对县域土壤养分合理采样数目进行讨论,比较两种方法各自的优越性。结果表明:碱解氮和速效钾均检测出3个全局离散样点,有效磷全局离群样点数目为7,三种养分局部离群样点检测数目分别为89、90和92;三种土壤养分均表现出很强的空间相关性,变异系数随着离群样点去除而降低;对于土壤养分大体概况研究,Cochran方法确定样本较为适合,而由克里金插值法确定的合理采样数目更能精确地反映局部土壤养分空间状况。 相似文献
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C. H. Bock P. J. Cotty 《European journal of plant pathology / European Foundation for Plant Pathology》2006,114(4):357-362
Three techniques (cyclone samplers, filter samplers and rotorods) were evaluated for sampling airborne propagules of Aspergillus flavus in a cultivated region of southwest Arizona. Analysis of variance indicated no significant difference between cyclone and
filter samplers in quantity of colony forming units caught, but there was a positive correlation between catches of the three
separate impaction samplers (r = 0.84–0.99, P>0.05). There was no detectable correlation between impaction sampler catches and cyclone catches (r=0.12–0.33; P>0.05). Cyclone samplers collected a dry sample that was easy to process for quantification of fungal propagules. Size of
conidia of A. flavus (combined with filter retention studies) suggests that the predominant propagules caught by the cyclone sampler were conidia,
rather than sclerotia or infected vegetative matter. Using a water-soluble coating, rotorods collected viable conidia of A. flavus under controlled environment conditions, but not in the field, although viable propagules of other fungi were caught, including
other Aspergilli. In the desert environment the rotorods became overloaded with particles of dust if operated for more than 2 h. Where isolate
culture is required, cyclone samplers are ideal for collecting airborne A. flavus propagules in dry climates. 相似文献
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甘肃狭啮卵在花椒园中的空间分布型及抽样技术 总被引：1，自引：0，他引：1
应用6种分布型指数法分析判定了甘肃狭啮Stenopsocus gansuensis卵在花椒园中的空间分布型,利用Taylor幂法则和Iwao回归方程分析聚集原因,结果表明,田间甘肃狭啮卵呈聚集分布,kc值为2.7934,符合负二项分布;其种群聚集原因是由本身行为习性所致。在此基础上,应用Iwao的理论抽样数模型建立了甘肃狭啮卵的田间理论抽样数公式：N=（t/D）2（1.7673）/m＋0.19887;根据Kuno新的序贯抽样法通式建立了该种群序贯抽样公式：Tn=1.7673/（D20-0.19887/n）。 相似文献
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本文研究了葛藤天敌紫茎甲Sagra femorata Lichtenstein的空间水平分布和垂直分布，结果表明：(1)紫茎甲幼虫在水平呈聚集分布，基本成分是个体群，且具聚集度对密度的依赖性，幼虫田间理论抽样公式N=(3．3401／M^ 0．5147])／D^2；(2)紫茎甲幼虫垂直分布符合负二项分布和核心分布。 相似文献
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为明确茶网蝽Stephanitis chinensis Drake的空间分布格局及其抽样技术,应用6种聚集度指标、Taylor幂法则及Iwao的回归模型分析了茶网蝽成虫、若虫的空间分布型,利用聚集均数分析其聚集原因,使用空间格局参数确定了其理论抽样数和若虫序贯抽样模型。结果表明,成虫、若虫空间分布型均呈密度依赖性负二项聚集分布,基本成分为个体群,个体间相互吸引。成虫聚集是由环境因素所引起,若虫密度低于2.624 9头/叶时聚集是由环境因素引起,若虫密度高于2.624 9头/叶时由环境因素与昆虫自身聚集习性共同引起。对若虫进行序贯抽样,当防治阈值为4头/叶、分布临界值为1.96时,防治上、下限方程分别为：■和■,百叶若虫量达到471头以上时需要进行防治。 相似文献
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介绍六点始叶螨(Eotetranychus sexmaculatus Riley)Iwao序贯抽样方案的设计和在田间调查中的应用。六点始叶螨的Iwao序贯抽样公式的上限T1=5n+1.64(5×[(0.135+1)×5+(1.375-1)×52])(1/2)、下限T0=5n-1.64(5×[(0.135+1)×5+(1.375-1)×52])(1/2)。在相同的置信水准下,序贯抽取的样本含量明显比常规抽样的少。 相似文献