排序方式: 共有27条查询结果,搜索用时 364 毫秒
1.
Andrei Canarache Iuliu Colibas Maria Colibas Ion Horobeanu Viorica Patru Horia Simota Theodor Trandafirescu 《Soil & Tillage Research》1984,4(2):199-213
Results of field experiments with soil compaction induced by wheel traffic applied uniformly to cover the entire surface of the experimental plots are reported. Compaction was done immediately before sowing, and each year, in each location, the same treatments were repeated on the same plots. The number of tractor passes varied between 0 and 30. The experiments were conducted during the 1978–1981 period in four locations with different soil and climatic conditions.Changes in soil physical properties, as well as in the yield of maize grain, were shown to be related to the number of tractor passes according to regression formulae of the type: Y = aXb. Most of the changes were recorded between 0 and 8–10 passes, while with more than 15–20 passes changes became negligible. The average maximum increase in bulk density was 20–25% as compared with the non-compacted control plot, and the average maximum decrease in yield was 46%. Moisture content in the compacted control plot, and the was 2–3% (w/w) lower than in the control plot, except for the soils with poor drainage where the lower part of the compacted topsoil showed an increase in moisture content. Air content in the compacted plots often dropped below 10, and occasionally to nearly 0% (v/v). For three of the four locations, grain yield of maize linearly decreased by 13 kg ha?1 (or 0.18% of the control plot yield) for each 1 kg m?3 increase in bulk density. 相似文献
2.
Bita I Yang JK Jung YS Ross CA Thomas EL Berggren KK 《Science (New York, N.Y.)》2008,321(5891):939-943
Self-assembling materials are the building blocks of bottom-up nanofabrication processes, but they need to be templated to impose long-range order and eliminate defects. In this work, the self-assembly of a thin film of a spherical-morphology block copolymer is templated using an array of nanoscale topographical elements that act as surrogates for the minority domains of the block copolymer. The orientation and periodicity of the resulting array of spherical microdomains are governed by the commensurability between the block copolymer period and the template period and is accurately described by a free-energy model. This method, which forms high-spatial-frequency arrays using a lower-spatial-frequency template, will be useful in nanolithography applications such as the formation of high-density microelectronic structures. 相似文献
3.
Gully development in the Moldavian Plateau of Romania 总被引:1,自引:0,他引:1
Gully erosion has been recognized as an important environmental threat in the Moldavian Plateau of Eastern Romania. The main objective of this study was to define the process-based gully development by providing quantitative information from long-term field measurements in small catchments.Three main areas of monitoring gullies were explored: aerial photographs of flights in 1960 and 1970, classical leveling and repeated survey through a particular close stakes grid after 1980. The Caesium-137 technique has been used effectively in the areas of deposition of gully sediments to obtain reliable information on dating specific levels of sediments and to provide chronological measures of gully development.Most of the discontinuous gullies exhibit both proper gullying, mainly if not exclusively by gully head advance, and aggradation of the gully basin floor. Results indicated that the mean gully head retreat was 0.92 m year− 1 and the mean areal gully growth was 17.0 m2 year− 1. Both values indicate a slow erosion rate for this area. The average annual regime of gullying is pulsatory, one that is best described by great fluctuations. Conventional measurements on sedimentation over the period 1987–1997 indicate a higher rate of aggradation in the upper half of the gully floor. Information on the Caesium-137 depth profile was used to provide estimates of a mean sedimentation rate of 4.4 cm year− 1 over the period 1963–1996 and 2.5 cm year− 1 after 1986 for the short successive discontinuous gullies. A new classification of the discontinuous gullies based on two criteria, respectively, the field patterns and the rate of aggradation within the gully basin floor was established.For continuous gullies, linear gully head retreat, areal gully growth and eroded material rates were quantified for three periods (1961–1970, 1971–1980 and 1981–1990). Results indicate that gully erosion has decreased since 1960. This gullying decline is due to the rainfall distribution, and the increased influence of soil conservation practices. The mean gully head retreat of 12.5 m year− 1 between 1961–1990 was accompanied by a mean areal gully growth of 366.8 m2 year− 1 and a mean erosion rate of 4168 t year− 1. As with discontinuous gullies, continuous gullies showed pulsatory development.The critical period for gullying over 1981–1996 covers 4 months from Mid March to Mid July in an area with mean annual precipitation around 500 mm. Another main finding of this 16-year stationary monitoring was that 57% of the total gullying occurred during the cold season, with the remainder during the warm season. Of the total gully growth, 66% results from only four years (1981, 1988, 1991 and 1996), when a greater amount of precipitation fell. 相似文献
4.
The socio-economic structure of the breeding farms of Franches-Montagnes horses (FM) in Switzerland is evaluated on the basis of an investigation carried out in 2002 by the Swiss FM breeding federation. Questionnaires were sent to 3500 of its members and the results include data from 968 breeding enterprises, housing a total of 3965 FM. The quality of the husbandry of FM varies according to factors such as the altitude and the geographical situation of the farms and studs. Socio-economic parameters, such as the role of FM in the business, their use (breeding, driving, riding) and the age and level of professional education of the owners may also have an effect on standards of husbandry. The results show that the owners for whom FM represent a source of income more frequently keep their horses in standing stalls, but give them more time to exercise at liberty than the horses belonging to amateur breeders. Younger and better educated breeders are more likely to house their animals in groups. 相似文献
5.
6.
Winfried Schröder Stefan Nickel Simon Schönrock Roman Schmalfuß Werner Wosniok Michaela Meyer Harry Harmens Marina V. Frontasyeva Renate Alber Julia Aleksiayenak Lambe Barandovski Oleg Blum Alejo Carballeira Maria Dam Helena Danielsson Ludwig De Temmermann Anatoly M. Dunaev Barbara Godzik Katrin Hoydal Zvonka Jeran Gunilla Pihl Karlsson Pranvera Lazo Sebastien Leblond Jussi Lindroos Siiri Liiv Sigurður H. Magnússon Blanka Mankovska Encarnación Núñez-Olivera Juha Piispanen Jarmo Poikolainen Ion V. Popescu Flora Qarri Jesus Miguel Santamaria Mitja Skudnik Zdravko Špirić Trajce Stafilov Eiliv Steinnes Claudia Stihi Ivan Suchara Lotti Thöni Hilde Thelle Uggerud Harald G. Zechmeister 《Annals of Forest Science》2017,74(2):31
Key message
Moss surveys provide spatially dense data on environmental concentrations of heavy metals and nitrogen which, together with other biomonitoring and modelling data, can be used for indicating deposition to terrestrial ecosystems and related effects across time and areas of different spatial extension.Context
For enhancing the spatial resolution of measuring and mapping atmospheric deposition by technical devices and by modelling, moss is used complementarily as bio-monitor.Aims
This paper investigated whether nitrogen and heavy metal concentrations derived by biomonitoring of atmospheric deposition are statistically meaningful in terms of compliance with minimum sample size across several spatial levels (objective 1), whether this is also true in terms of geostatistical criteria such as spatial auto-correlation and, by this, estimated values for unsampled locations (objective 2) and whether moss indicates atmospheric deposition in a similar way as modelled deposition, tree foliage and natural surface soil at the European and country level, and whether they indicate site-specific variance due to canopy drip (objective 3).Methods
Data from modelling and biomonitoring atmospheric deposition were statistically analysed by means of minimum sample size calculation, by geostatistics as well as by bivariate correlation analyses and by multivariate correlation analyses using the Classification and Regression Tree approach and the Random Forests method.Results
It was found that the compliance of measurements with the minimum sample size varies by spatial scale and element measured. For unsampled locations, estimation could be derived. Statistically significant correlations between concentrations of heavy metals and nitrogen in moss and modelled atmospheric deposition, and concentrations in leaves, needles and soil were found. Significant influence of canopy drip on nitrogen concentration in moss was proven.Conclusion
Moss surveys should complement modelled atmospheric deposition data as well as other biomonitoring approaches and offer a great potential for various terrestrial monitoring programmes dealing with exposure and effects.7.
– |
• Construction cost (g glucose g−1), chemical composition and morphology of leaves of beech (Fagus sylvatica L.) and two co-occurring valuable broadleaved species (sycamore maple — Acer pseudoplatanus L. — and ash — Fraxinus excelsior L.) were investigated along a horizontal light gradient (3–60% of above canopy radiation) and from top to bottom within the
crowns in a fairly even-aged mixed-species thicket established by natural regeneration beneath a patchy shelterwood canopy. 相似文献
8.
The quality of husbandry of Franches-Montagnes horses (FM) in Switzerland is evaluated on the basis of an investigation carried out in 2002 by the Swiss FM breeding federation. Questionnaires were sent to 3500 of its members and the results include data from 968 breeding enterprises, housing a total of 3965 FM: 46.1% were breeding mares (61.0% with foal at foot), 26.5% young stock, 1.3% stallions and 26.0% non breeding stock (74.6% of which were pleasure horses and 25.4% working horses). 57.6% of the FM were housed in individual boxes with or without permanent outdoor access, 25.4% were hold in groups with or without permanent outdoor access, the remaining 17.0% were kept in standing stalls. 95.0% of the FM had at least visual contact with other equines and 99.2% had sufficient light in their stable. 88.1% were stabled on long stalk straw, while only 4.3% were bedded on other materials other than straw. The average time spent at pasture per horse and per week ranged from 96.5 +/- 51.6 hours in summer to 27.2 +/- 26.7 hours in winter. On average, a FM is used for 8.3 +/- 6.5 hours per week. Horses with an paddock at their disposal spend an average of 39.8 +/- 45.9 hours there per week. 相似文献
9.
Ion Catalin Petri?an Burghard von Lüpke Any Mary Petri?an 《Journal of Forest Research》2012,17(2):164-174
The reaction of young beech (Fagus sylvatica L.) and Douglas fir (Pseudotsuga
menziesii (Mirb.) Franco) saplings on competition of two types of vegetation—(1) gramineous with mainly Agrostis capillaries, Calamagrostis epigejos, Deschampsia flexuosa, and (2) small shrubs with mainly Rubus fruticosus and R. idaeus—on clear cuts on two sites was studied for 2 years. Half the sample saplings were released from competing vegetation by repeated
herbicide applications. This treatment significantly raised the diameter increment in both species at the site with higher
competition intensity, and more strongly after the removal of small shrubs than after the removal of grasses. Sapling length
increment was not significantly affected. After being released from small shrubs, saplings of both species developed a smaller
specific fine root length (cm g−1 fine root biomass) than unreleased saplings during the second year which was characterized by low rainfall. Root nitrogen
concentration significantly increased after weed control in both vegetation types. Sapling foliar content of main nutritional
elements was negatively related to dry mass and total chemical content of surrounding ground vegetation. Based on these results,
a release from ground vegetation could be a useful tool to improve growth of planted beech and Douglas-fir saplings on sites
with well-developed small shrubs competition (mainly by Rubus fruticosus and R. idaeus), or under fairly dry conditions. 相似文献
10.
Plum pox virus (PPV) belongs to the genus Potyvirus that contains the largest number of virus species infecting plants. Its virus genome has been extensively characterised and sequenced. However, few data are available on its interactions with woody host plants. We therefore focused, in the past 4 years, both on the cellular and molecular aspects of the compatible and incompatible Prunus /PPV interactions. GFP (Green fluorescent protein)-tagged PPV and in situ hybridisation were used to compare the localization of viral particles in stems and leaves of susceptible and resistant apricot cultivars. In parallel, molecular tools were developed through the cloning and characterization of polymorphic, homologous resistance genes and of candidate genes involved in the expression of Prunus /PPV interactions. Candidate genes are currently used to target genomic regions involved in resistance or susceptibility and to identify molecular markers indispensable for further marker assisted selection for resistance to sharka disease. 相似文献
|