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991.
Chris Klok Jack Faber Guido Heijmans Jos Bodt Annemariet van der Hout 《Biology and Fertility of Soils》2007,43(5):549-556
In this paper we report on the influence of clay content and acidity of soil on growth and reproduction of the epigeic earthworm
species Lumbricus rubellus (Hoffm.), which is common in most temperate soils and abundant in grasslands. Growth, cocoon production and survival of L. rubellus were tested in 12 Dutch soils which differed in soil properties. A matrix model was used to assess the population-level consequences
of changes in growth and reproduction. Soil acidity had a strong negative effect on earthworm survival, and the maturation
weight decreased with clay content. Individual weight gain in L. rubellus decreased with both acidity and clay content. The acidity of soils had a larger influence on population growth rate than
the clay content. The acidity of the soil also changed the population composition towards younger age classes, whereas in
soils rich in clay, the population composition did not change. The average individual weight of L. rubellus in clayey soils, however, was lower compared with that in soils low in clay, a result that agrees with literature data. 相似文献
992.
993.
994.
Carlo Gaetan Matteo Grigoletto 《Journal of Agricultural, Biological & Environmental Statistics》2007,12(4):434-449
In this article, we propose a spatial model for analyzing extreme rainfall values over the Triveneto region (Italy). We assess
the existence of a long-term trend in the extremes. To integrate data coming from the different stations, we propose a hierarchical
model. At the first level, for each monitoring station we model data by making use of a generalized extreme value distribution;
at the second level, we combine results from the first stage by exploiting recent advances in modeling nonstationary spatial
random fields. 相似文献
995.
Spatial heteroscedasticity may arise jointly with spatial autocorrelation in lattice data collected from agricultural trials
and environmental studies. This leads to spatial clustering not only in the level but also in the variation of the data, the
latter of which may be very important, for example, in constructing prediction intervals. This article introduces a spatial
stochastic volatility (SSV) component into the widely used conditional autoregressive (CAR) model to capture the spatial clustering
in heteroscedasticity. The SSV component is a mean zero, conditionally independent Gaussian process given a latent spatial
process of the variances. The logarithm of the latent variance process is specified by an intrinsic Gaussian Markov random
field. The SSV model relaxes the traditional homoscedasticity assumption for spatial heterogeneity and brings greater flexibility
to the popular spatial statistical models. The Bayesian method is used for inference. The full conditional distribution of
the heteroscedasticity components can be shown to be log-concave, which facilitates an adaptive rejection sampling algorithm.
Application to the well-known wheat yield data illustrates that incorporating spatial stochastic volatility may reveal the
spatial heteroscedasticity hidden from existing analyses. 相似文献
996.
Assessing soil erosion and control factors by the radiometric technique in the Boussouab catchment,Eastern Rif,Morocco 总被引:1,自引:0,他引:1
In the Eastern Rif of N Morocco, soil conservation is seriously threatened by water erosion. Large areas of soil have reached an irreversible state of degradation. In this study, the 137Cs technique was used to quantify erosion rates and identify the main factors involved in the erosion process based on a representative catchment of the Eastern Rif. To estimate erosion rates in terms of the main factors affecting soil losses, samples were collected taking into account the lithology, slope and land use along six selected transects within the Boussouab catchment. The transects were representative of the main land uses and physiographic characteristics of that Rif sector. The reference inventory for the area was established at a stable, well preserved, matorral site (value of 4250 Bq m− 2). All the sampling sites were eroded and 137Cs inventories varied widely (between 245 and 3670 Bq m− 2). The effective soil losses were also highly variable (between 5.1 and 48.8 t ha− 1 yr− 1). Soil losses varied with land use. The lowest average values were on matorral and fallow land (10.5 and 15.2 t ha− 1 yr− 1, respectively) but much higher with alfa vegetation or cereal crops (31.6 and 27.3, respectively). The highest erosion rate was on a badland transect at the more eroded part of the catchment, with rates exceeding 40 t ha− 1 yr− 1 and reaching a maximum of 48.8 t ha− 1 yr− 1.The average soil losses increased by more than 100% when the slope increased from 10° (17.7 t ha− 1 yr− 1) to 25° (40. 8 t ha− 1 yr− 1). Similar results were obtained when comparing erosion rates in soils that were covered by matorral with respect to those under cultivation. Lithology was also a key factor affecting soil loss. Soils on marls were more erodible and the average erosion rates reached 29.36 t ha− 1 yr− 1, which was twice as high as soils on the glacis and old fluvial terraces (average rates of 14.98 t ha− 1 yr− 1). The radiometric approach was very useful to quantify erosion rates and to examine the pattern of soil movement. The analysis of main erosion factors can help to promote rational soil use and establish conservation strategies in the study area. 相似文献
997.
Gemechu Keneni Mussa Jarso Tezera Wolabu Getnet Dino 《Genetic Resources and Crop Evolution》2005,52(5):539-549
An experiment was conducted in 2001 at Holetta and Kulumsa, Ethiopia, to study the extent and pattern of genetic diversity
in Ethiopian field pea (Pisum sativum L.) landraces. One hundred forty-eight germplasm accessions were grown in an alpha lattice design with 2 replications. Data
on 12 traits were collected and analyzed. Differences among the accessions were significant for most of the traits (except
number of seeds/ pod) at each location even though differences pooled over location were mostly non-significant. The accessions
were grouped into five clusters of different sizes. Accessions from the southern part of the country (Arsi) distributed overall
clusters while those from the northern half (North and South Wello, North Gonder and North Shewa) fell into clusters C1 to C3. Cumulative effects of a number of characters dictated differentiation of the accessions into clusters. There was no definite
relationship between geographic diversity and genetic diversity as overlapping was encountered in clustering pattern among
accessions from different parts of the country. Accessions from different regions might have similar genetic background and
those from the same origin might also have different genetic background. Therefore, geographic diversity should not necessarily
be used as an index of genetic diversity and parental selection should be based on a systematic study of genetic diversity
in a specific population. Genetic distances among most of the clusters were significant that crosses between parents selected
out of them are expected to generate desirable genetic recombination. Selection should also consider the special advantages
of each cluster and each accession within a cluster. Future germplasm collection, conservation and breeding efforts should
focus not only on inter-regional diversity but also on intra-regional diversity. 相似文献
998.
Gemechu Keneni Mussa Jarso Tezera Wolabu Getnet Dino 《Genetic Resources and Crop Evolution》2005,52(5):551-561
A field experiment was conducted in 2001 at Holetta and Kulumsa, Ethiopia, to study genetic diversity in Ethiopian faba bean
(Vicia faba L.) landraces. One hundred sixty random germplasm accessions were grown in an alpha lattice design with two replications. Data
on 12 traits were collected and analyzed. Significant differences were observed among the accessions for most of the traits
(except number of pods/podding nodes) at each location even though differences pooled over location were mostly non-significant.
Cluster analysis distinguished seven diversity classes of different sizes. Accessions from the northern half of the country
(North and South Wello, North Gonder and North Shewa) were closely related while those from the southern part of the country
(Arsi) were highly diverse. Cumulative effects of a number of characters dictated differentiation of the accessions into clusters.
Some overlapping were encountered between accessions from the northern and those from the southern parts of the country. The
study revealed that accessions from different regions might have similar genetic background and those from the same origin
might also have different genetic background. Therefore, geographic diversity should not necessarily be used as an index of
genetic diversity and parental selection should be based on a systematic study of genetic diversity in a specific population.
Genetic distances between most of the clusters were significant that crosses between parents selected out of them are expected
to generate desirable progenies. Future germplasm collection, conservation and utilization strategies should put more focus
not only on inter-regional diversity in the country as a whole but also on intra-regional diversity in Arsi. 相似文献
999.
Hongjie Li Robert L. Conner Qin Chen Robert J. Graf André Laroche F. Ahmad A. D. Kuzyk 《Genetic Resources and Crop Evolution》2005,51(8):827-835
Wheat streak mosaic virus (WSMV), vectored by the wheat curl mite (WCM),Aceria tosichella Keifer, is one of the most destructive viral diseases of wheat found in many wheat producing areas of the world. Host resistance is the most effective method for controlling this disease and its vector. Symptomatological analysis and enzyme-linked immunosorbent assay (ELISA) were used to characterize WSMV-resistance in wheat-alien partial amphiploid lines and their derivatives. The results showed that most of partial amphiploids derived fromThinopyrum ponticum andTh. intermedium were free of systemic symptoms with very low ELISA readings that were similar to that of the non-inoculated Chinese Spring control. While the partial amphiploid lines 693 and PWM706 were identified as new genetic resources of resistance to WSMV. The present study demonstrated that both symptomatological and ELISA methods efficiently assessed WSMV-resistance in the wheat-alien hybrids and systemic symptom incidence and ELISA absorbance readings were highly correlated (r
2 = 0.8658–0.9323) over time following inoculation. The ELISA results also indicated that the virus did not buildup in the plant tissues of these virus-resistant partial amphiploids. Similar results were observed in chromosome translocation and substitution lines that have the geneWsm1 conferring WSMV resistance. However, the lines containing the geneWsm1 and all the partial amphiploid lines, except Agrotana, were susceptible to the WCM. One line derived from a cross of wheat and Agrotana, was effective in controlling the spread of WSMV and was highly resistant to the WCM. Another line and an accession ofTriticum dicoccoides (Koern.) Schweinf. were highly susceptible to WSMV and WCM. Early disease development was delayed in a new hard red winter cultivar McClintock. The partial WSMV-resistance of McClintock was demonstrated by initially low ELISA readings, and a lower percentage of infected plants than other WSMV-susceptible wheat. The use of the identified promising sources of resistance to WSMV and the WCM in wheat breeding is discussed.LRC Contribution No. 387-01061. 相似文献
1000.
Stephanie L. Meadows-Shropshire Chris Gennings W. Hans Carter 《Journal of Agricultural, Biological & Environmental Statistics》2005,10(1):104-117
In the analysis of mixtures of drugs/chemicals it is often of interest to test for the presence of interaction. If the hypothesis
of no interaction (additivity) is not rejected, then the analyst may reasonably claim additivity if and only if the study
is powered to a desired (e.g., biologically meaningful) level. The objective of this article is to address the sample size
and power issues related to testing the hypothesis of additivity at specified mixture points. The study of disinfectant by-products
(DBPs) found in drinking water, described in earlier literature, is used to illustrate the procedures for estimating power
and sample sizes for detecting interactions at specified mixtures. The four trihalomethanes used in the study are bromodichloromethane
(BDCM), chlorodibromomethane (CDBM), chloroform (CHCl3), and bromoform (CHBr3) 相似文献