排序方式: 共有189条查询结果,搜索用时 62 毫秒
91.
Simone Peletto Matteo Perucchini Cristina Ac��n Mark P. Dalgleish Hugh W. Reid Roberto Rasero Paola Sacchi Paula Stewart Maria Caramelli Ezio Ferroglio Elena Bozzetta Daniela Meloni Riccardo Orusa Serena Robetto Silvia Gennero Wilfred Goldmann Pier Luigi Acutis 《Journal of veterinary science (Suw?n-si, Korea)》2009,10(2):115-120
The genetics of the prion protein gene (PRNP) play a crucial role in determining the relative susceptibility to transmissible spongiform encephalopathies (TSEs) in several mammalian species. To determine the PRNP gene variability in European red deer (Cervus elaphus), roe deer (Capreolus capreolus) and chamois (Rupicapra rupicapra), the PRNP open reading frame from 715 samples was analysed to reveal a total of ten single nucleotide polymorphisms (SNPs). In red deer, SNPs were found in codons 15, 21, 59, 78, 79, 98, 136, 168 and 226. These polymorphisms give rise to 12 haplotypes, and one of which is identical to the PRNP of American wapiti (Rocky Mountain elk, Cervus elaphus nelsoni). One silent mutation at codon 119 was detected in chamois and no SNPs were found in roe deer. This analysis confirmed that European wild ruminants have a PRNP genetic background that is compatible with TSE susceptibility, including chronic wasting disease. 相似文献
92.
Ariel E. Lugo Oscar J. Abelleira Alexander Collado Christian A. Viera Cynthia Santiago Diego O. V��lez Emilio Soto Giovanni Amaro Graciela Char��n H��ctor Col��n Jr. Jennifer Santana Jos�� L. Morales Katherine Rivera Luis Ortiz Luis Rivera Mianel Maldonado Natalia Rivera Norelis J. V��zquez 《New Forests》2011,42(3):267-283
The African tulip tree, Spathodea campanulata, the most common tree in Puerto Rico, forms novel forest types with mixtures of native and other introduced tree species. Novel forests increase in area in response to human activity and there is no information about their biomass accumulation and nutrient cycling. We established allometric relationships and chemically analyzed plant parts of African tulip trees to determine the concentration and standing stock of chemical elements (C, N, P, K, Ca, Mg, S, Mn, Al, Fe, Na), and ash. Trees ranged in diameter at breast height from 8 to 85 cm and in height from 8.8 to 28 m. The concentrations of N, P, K, and Ca in leaves of the African tulip tree were similar to those of the native pioneer Cecropia schreberiana and higher than those of mature forest tree species in Puerto Rico. The over bark wood volume of African tulip trees in nine forest stands where it was dominant ranged from 163 to 849 m3/ha. Aboveground biomass ranged from 60 to 296 Mg/ha, and N and P stocks ranged from 190 to 988 and 32 to 137 kg/ha, respectively. Novel forests on abandoned agricultural lands can store more biomass and elements than native and plantation forest stands of similar age. 相似文献
93.
Mercedes Garc��a-Sancho ��ngel Sainz Alejandra Villaescusa Antonio Rodr��guez Fernando Rodr��guez-Franco 《Journal of veterinary science (Suw?n-si, Korea)》2011,12(2):165-169
Distended lacteals, described as expanded white villi in duodenum, are strongly indicative of primary intestinal lymphangiectasia. In the present study, we evaluated the significance of white spots present in the duodenal mucosa of dogs with lymphocytic plasmacytic enteritis (LPE). Fifty dogs with LPE were included in this study, and white spots were detected in the duodenal mucosa in 22 dogs during endoscopy. Hypoproteinemia was more frequent in dogs with white spots than in dogs without spots (p = 0.02). Serum protein and albumin concentration were significantly lower in LPE dogs with white spots (p = 0.038) compared to LPE dogs without white spots (p = 0.039). There was a significant correlation between white spots density and lymphatic dilatation histological scores (p = 0.023; ρ = 0.481). These results suggest that the presence of white spots in the duodenal mucosa of dogs is not a finding exclusive for intestinal lymphangiectasia. Low serum protein and albumin concentrations together with lymphatic dilatation seem to be related to the presence of white spots in the duodenal mucosa of LPE dogs. 相似文献
94.
Agroforestry Tree Seed Production and Supply Systems in Malawi 总被引:1,自引:1,他引:0
Betserai I. Nyoka Simon A. Mng��omba Festus K. Akinnifesi Oluyede C. Ajayi Gudeta Sileshi Ramni Jamnadass 《Small-Scale Forestry》2011,10(4):419-434
A sustainable agroforestry tree germplasm supply system is vital to resource-constrained smallholder farmers who depend on
agroforestry to improve the productivity of their farm enterprises. Successful adoption of agroforestry hinges on the development
of a sustainable agroforestry tree germplasm supply system. This paper reviews the agroforestry tree seed supply system in
Malawi, with a view to determining its sustainability and quality. Currently, more than 90% of the documented agroforestry
tree seed distributed to farmers is produced by smallholder farmers collected mainly from scattered farmland trees, the remainder
being produced from seed orchards and seed stands owned or controlled by research organizations. Three organizations—namely
the Land Resources Centre (LRC), National Tree Seed Centre (NTSC) of the Forestry Research Institute of Malawi (FRIM) and
the World Agroforestry Centre (ICRAF)—were identified as major procurers of agroforestry tree seed produced by smallholder
farmers. Agroforestry germplasm is distributed to farmers by non-governmental organizations (NGOs) and government agricultural
and forestry extension departments. The procurement and distribution of germplasm to farmers is in general effective. The
major challenge to sustainability of agroforestry tree germplasm distribution in Malawi is dependence on donor funding. The
agroforestry tree seed system is, to some extent, sustainable with regards to production, although the genetic quality of
the germplasm is low. Germplasm storage facilities at national level are available and possibly adequate, but knowledge and
information on effective low-cost tree germplasm storage systems at household level are limited. Sustainability could be enhanced
by strengthening of grass-root organizations involved in tree seed production to institutionalize the distribution through
farmer–farmer exchange. There is also a need to support the development, promotion and adoption of low-cost tree germplasm
storage facilities by smallholder farmers. 相似文献
95.
David Janik Du?an Adam Tom��? Vr?ka Libor Hort Pavel Unar Kamil Kr��l Pavel ?amonil David Horal 《European Journal of Forest Research》2011,130(2):197-208
Tree species composition of Central European alluvial hardwood forests has changed with the arrival of flood-intolerant and mesic species. Within this group of tree species, a dominant role is played by field maple (Acer campestre) and European hornbeam (Carpinus betulus). This study was performed in the Lanzhot natural forests at the confluence of the Morava and the Dyje Rivers, which are considered to be one of the most natural alluvial hardwood forests in Central Europe and where the absence of the direct influence by humans for 75 years has allowed spontaneous development. Our basic research questions were as follows: (1) does the mutual proportion and structure of field maple and hornbeam populations change along an elevation gradient of 4 m in an alluvial forest and (2) does the tree spatial pattern of field maple and hornbeam change along this gradient? The study found significant differences in the development of hornbeam and field maple populations with increasing elevation in an alluvial hardwood forest. While the strength of the hornbeam population clearly increases with increasing elevation, the field maple population does not. Compared to hornbeam, field maple is closer to the r-strategy side of the K-r continuum on alluvial sites. Our study reveals that field maple and hornbeam are mainly distributed in clusters on alluvial sites. Both species are concentrated at places with lower flooding intensity, i.e. to higher elevation sites. The study shows that tree spatial patterns could change dynamically along a short elevation gradient in alluvial hardwood forest. 相似文献
96.
Irrigation scheduling services (ISS) provide farmers with recommendations on timing and amount of irrigation, thus contributing
to improving on-farm water management. There are wide variations in the level of services, from providing regional water use
guidelines to local, on-farm advisory services. An ISS (ISS-ITAP) was created in 1988 in Albacete, Central Spain, a province
encompassing 100,000 ha which are irrigated mostly with groundwater. The ISS-ITAP first offered general information on crop
water requirements (ET), and after 1994 field-specific scheduling services were provided to growers. By 2005 the ISS-ITAP
had expanded its services to over 33,500 ha, corresponding to about 30% of the irrigable area. The evolution of irrigation
performance in a number of individual farms was followed over 10 years, and it was found that the proportion of fields which
were adequately irrigated increased from 50 to over 70% in that period. Meanwhile, the proportion of deficit-irrigated fields
declined from 20 to 10%, while the proportion of over-irrigated fields which also had initially decreased from 20 to 10%,
went back to 20% at the end of the study period. To assess the benefits and costs of the ISS-ITAP, a comparison of the yields
achieved in the scheduled farms against those obtained in the rest of the province was carried out. When the Service was evaluated
in economic terms, using information from 2003, the pay-back was 2 years and the internal rate of return was 59.1%, highlighting
the high returns on the public funds invested by ISS-ITAP to provide irrigation advisory service to growers in the Albacete
province. 相似文献
97.
Zero tillage and controlled traffic have been proposed as means for more productive and sustainable irrigated farming. Both
practices affect soil infiltration characteristics and, therefore, should have effects on sprinkler irrigation performance.
This study compared water infiltration and runoff in three sprinkler irrigation tests performed on an alluvial loam soil at
different times during a maize (Zea mays L.)–cotton (Gossypium hirstium L.) rotation under two soil managements: permanent beds with crop residue retention (PB: planting beds maintained unaltered
from year to year) and conventional beds with residues incorporated with tillage (CB: disc and chisel ploughing followed by
rotavator pass and bed forming every year). Traffic was controlled and two types of furrows were distinguished in both tillage
systems: with (+T) and without (−T) wheel traffic. The irrigation tests were performed on maize at full cover, on bare soil
just before cotton sowing and on cotton with 50% ground cover. Infiltration and runoff were affected notably by both traffic
and soil management. The soil under PB infiltrated more water than under CB, and −T furrows more than +T furrows. Considering
the combined treatments, −T furrows in the CB system infiltrated more water than +T furrows in the PB system. A sprinkler
irrigation model for simulating water application and soil infiltration and runoff was formulated. The model was used to analyse
irrigation performance under infiltration characteristic of the CB and PB systems in trafficked and non-trafficked furrows.
Five irrigation performance indicators were used to assess the various combinations of tillage and traffic: Wilkox–Swailes
coefficient of uniformity; application efficiency; deep percolation ratio; tail water ratio; and adequacy. The model was used
to develop operation diagrams and provided guidelines for making irrigation decisions in the new controlled traffic/permanent
bed system and in a standard conventional system. 相似文献
98.
Robson Andr�� Armindo Tarlei Arriel Botrel Tiago Capello Garzella 《Irrigation Science》2011,29(3):233-240
Due to the rapid depletion of water resources, water must be used more efficiently in agriculture to maintain current levels
of yield in irrigated areas. The efficiency of irrigation systems can be increased by adjusting the amount of water applied
to specific conditions of soil and crop, which may vary in a field. Taking into account spatial and temporal variability,
it is evident that an equipment capable of providing different irrigation levels is necessary to meet the water requirement
of the soil. This work aims to develop and evaluate a flow rate sprinkler to be used in center pivots or linear moving irrigation
systems, with potential for utilization in irrigation scheduling. A prototype was developed by duplicating its calibrations,
and discharge coefficient adjustment was carried out in the laboratory. To predict the flow rate, a successful model that
represented the operation of the flow rate sprinkler was established. The calibration of the flow rate sprinkler prototype
showed satisfactory statistical and technical results. Automation of the prototype was achieved by driving a step motor using
communication from the parallel port of a microcomputer, which was controlled by a software developed for this purpose. The
results were satisfactory and technically feasible. 相似文献
99.
This paper investigates the ability of linear genetic programming (LGP), which is an extension to genetic programming (GP)
technique, in daily pan evaporation modeling. The daily climatic data, air temperature, solar radiation, wind speed, pressure
and humidity of three automated weather stations, Fresno, Los Angeles and San Diego in California, are used as inputs to the
LGP to estimate pan evaporation. The LGP estimates are compared with those of the Gene-expression programming (GEP), which
is another branch of GP, multilayer perceptrons (MLP), radial basis neural networks (RBNN), generalized regression neural
networks (GRNN) and Stephens–Stewart (SS) models. The performances of the models are evaluated using root mean square errors
(RMSE), mean absolute error (MAE) and determination coefficient (R
2) statistics. Based on the comparisons, it was found that the LGP technique could be employed successfully in modeling evaporation
process from the available climatic data. 相似文献
100.
Agricultural production has forced researchers to focus on increasing water use efficiency by improving either new drought-tolerant
plant varieties or water management for arid and semi-arid areas under water shortage conditions. A field study was conducted
to determine effects of seasonal deficit irrigation on plant root yield, quality and water use efficiency (WUE) of sugar beet
for a 2-year period in the semi-arid region. Irrigations were applied when approximately 50–55% of the usable soil moisture
was consumed in the effective rooting depth at the full irrigation (FI) treatment. In deficit irrigation treatments, irrigations
were applied at the rates of 75, 50 and 25% of full irrigation treatment on the same day. Irrigation water was applied by
a drip irrigation system. Increasing water deficits resulted in a relatively lower root and white sugar yields. The linear
relationship between evapotranspiration and root yield was obtained. Similarly, WUE was the highest in DI25 irrigation conditions
and the lowest in full irrigation conditions. According to the averaged values of 2 years, yield response factor (k
y
) was 0.93 for sugar beet. Sugar beet root quality parameters were influenced by drip irrigation levels in both years. The
results revealed that irrigation of sugar beet with drip irrigation method at 75% level (DI25) had significant benefits in
terms of saved irrigation water and large WUE, indicating a definitive advantage of deficit irrigation under limited water
supply conditions. In an economic viewpoint, 25% saving of irrigation water (DI25) caused 6.1% reduction in the net income. 相似文献