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951.
A systematic and quantitative approach to improve water use efficiency in agriculture 总被引:6,自引:2,他引:4
As the competition for the finite water resources on earth increases due to growth in population and affluence, agriculture
is faced with intensifying pressure to improve the efficiency of water used for food production. The causes for the relatively
low water use efficiency in agriculture are numerous and complex, including environmental, biological, engineering, management,
social, and economic facets. The complexity of the problem, with its myriads of local variations, requires a comprehensive
conceptual framework of the underlying physical and biological processes as the basis to analyze the existing situation and
quantify the efficiencies, and to plan and execute improvements. This paper proposes such a framework, based on the simple
fact that the overall efficiency of any process consisting of a chain of sequential step is the product of the efficiency
(i.e., output/input ratio) of its individual component steps. In most cases of water use, a number of process chains, both
branching and merging, are involved. Means to integrate the diverging and converging chains are developed and presented as
equations. Upscaling from fields to regions and beyond are discussed. This chain of efficiencies approach is general and can
be applied to any process composed of chains of sequential steps. Here the framework is used to analyze the systems of irrigated
and dryland crop production, and animal production on rangeland. Range of plausible efficiencies of each step is presented
as tables, with values separately for the poor and for the good situation of circumstances, management and technology. Causes
of the differences in efficiency of each step, going from water delivery to soil water extraction, transpiration, photosynthesis,
and conversion to crop biomass and yield, and to animal product are briefly discussed. Sample calculations are made to demonstrate
how modest differences in the efficiencies of the component steps are manifested as large to huge differences in the overall
efficiency. Based on an equation quantifying the impact of changes in efficiency of component steps on the overall efficiency,
it is concluded that generally, it is more effective to made modest improvements in several or more steps than to concentrate
efforts to improve one or two steps. Hence, improvement efforts should be systematic and not overly concentrated on one or
two components. The potential use of the same equation as the point of departure to optimize the allocation of economic resource
among the component steps to maximize the improvement in the overall water use efficiency is elaborated on. The chain of efficiencies
framework provides the means to examine the current levels of efficiency along the pathways of agricultural water use, to
analyze where inefficiencies lie by comparing with the range of known efficiency values in the tables presented, to assess
the potential improvements that may be achieved in various parts and their impact on the overall efficiency, and to aid in
the optimal allocation of resources for improvements.
相似文献
Theodore C. HsiaoEmail: |
952.
José AlvesJr Marcos V. Folegatti Larry R. Parsons Wije Bandaranayake Claudio R. da Silva Tonny J. A. da Silva Luís F. S. M. Campeche 《Irrigation Science》2007,25(4):419-428
The expansion of permanent trickle irrigation systems in Sao Paulo (Brazil) citrus has changed the focus of irrigation scheduling
from determining irrigation timing to quantifying irrigation amounts. The water requirements of citrus orchards are difficult
to estimate, since they are influenced by heterogeneous factors such as age, planting density and irrigation system. In this
study, we estimated the water requirements of young ‘Tahiti’ lime orchards, considering the independent contributions from
soil evaporation and crop transpiration by splitting the crop coefficient (Kc = ETc/ETo) into two separate coefficients; Ke,
a soil evaporation coefficient and Kcb, a crop transpiration coefficient. Hence, the water requirement in young ‘Tahiti’ lime
(ETy) is ETy = (Ke + Kcb) · ETo, where ETo is the reference crop evapotranspiration. Mature tree water requirement (ETm) is ETm = Kcb · ETo, assuming no soil water evaporation. Two lysimeters were used; one was 1.6 m in diameter and 0.7 m deep, and
the other was 2.7 m in diameter and 0.8-m deep. The first one was used to calculate evaporation and the second one was used
for transpiration. ETo was estimated by the Penman–Monteith method (FAO-56). The measurements were conducted during a period
between August 2002 and April 2005 in Piracicaba, Sao Paulo state, Brazil. The lysimeters were installed at the center of
a 1.0-ha plot planted with ‘Tahiti’ lime trees grafted on ‘Swingle’ citrumelo rootstock. The trees were 1-year old at planting,
spaced 7 × 4 m, and were irrigated by a drip irrigation system. During the study period, Kc varied between 0.6 and 1.22, and
Kcb varied between 0.4 and 1.0. The results suggested that for young lime trees, the volume of water per tree calculated by
Ke + Kcb is about 80% higher than the volume calculated using Kc. For mature trees, the volume of water per tree calculated
using just Kcb can be 10% less than using Kc. The independent influence of soil evaporation and transpiration is important to better understand the water consumption of
young lime trees during growth compared to mature lime trees. 相似文献
953.
Polycyclic aromatic hydrocarbons (PAHs) are one class of chemical compounds that (1) are present at low to trace levels in unburned cigarette filler, and (2) are predominantly generated during combustion. According to a recent report of the International Agency for Research on Cancer, 10 carcinogenic PAHs together with 53 other known carcinogens are present in cigarette smoke. Accurate quantification of these chemicals helps assess public health risk to both smokers and nonsmokers exposed to second-hand smoke. We have developed and validated a specific and sensitive method for measuring these 10 carcinogenic PAHs in the particulate phase of mainstream tobacco smoke. Cigarette smoke particulate, produced using standard machine smoking protocols, was collected on glass fiber Cambridge filter pads. The particulate matter was solvent extracted, purified by solid-phase extraction, and analyzed by liquid chromatography/atmospheric pressure photoionization tandem mass spectrometry using isotopically labeled analogues as internal standards. Our method's limits of detection ranged from 11 to 166 pg and achieved sufficient reproducibility and accuracy to provide useful information on a range of cigarettes having dramatically different machine-smoked tar and nicotine deliveries. The identity of each PAH analyte was established from chromatographic retention time, analyte-specific fragmentation patterns, and relative peak area ratios of the product/precursor ion pairs. This new method provides higher sensitivity, specificity, and throughput than did earlier methods. We found relatively consistent PAH levels among a selection of domestic full-flavor cigarettes. The PAH levels in smoke from highly ventilated light and ultralight cigarettes were low when smoked using ISO (International Organization for Standardization) conditions. However, if highly ventilated cigarettes were smoked under more intense conditions (e.g., larger or more frequent puffs, vents blocked), their PAH levels equaled or exceeded their full-flavor counterparts under ISO conditions. 相似文献
954.
Jeroen Peters Wojciech Sledz Jan H. W. Bergervoet Jan M. van der Wolf 《European journal of plant pathology / European Foundation for Plant Pathology》2007,117(2):97-107
An enrichment microsphere immunoassay (MIA) was developed, based on the Luminex xMAP® technology, for the simultaneous (duplex) detection of Pectobacterium atrosepticum (former name Erwinia carotovora subsp. atroseptica) (Pca) and Dickeya dianthicola (former name Erwinia chrysanthemi) (Dcd) in potato plant extracts. Target bacteria in the extracts were enriched for 48 h in a semi-selective broth containing polypectate under low oxygen conditions. Samples were subsequently incubated with antibody-coated colour-coded microspheres (beads) and with secondary antibodies conjugated with Alexa Fluor® 532, a reporter dye. Samples were analyzed with the Luminex analyzer, in which one laser identified each microsphere and another laser the reporter dye conjugated to the secondary antibodies. The assay required minimal sample preparation, could be completed in 1 h, was performed in 96 wells microtitreplates and required no wash steps. The limit of detection for the duplex enrichment MIA was 100–1000 cfu ml?1, which was a hundred times lower than of an enrichment-ELISA. Without enrichment, the sensitivity of MIA and ELISA was largely similar and ranged between 106 and 107 cells ml?1. No difference in sensitivity was found between a MIA in a single or duplex format. In a comparative test with non-infected potato plant extracts and extracts from plants infected with Pca or Dcd, results of the enrichment MIA correlated well with those of the enrichment ELISA and enrichment PCR. These results indicate that MIA can be reliably used for multiplex detection of soft rot Enterbacteriaceae in crude potato plant extracts. The technology is an attractive and cost-effective alternative to other detection methods, including ELISA. 相似文献
955.
In terrestrial ecosystems, gross nitrogen mineralisation is positively correlated to microbial biomass but negatively to soil
organic matter C-to-N ratios; the influence of the microbial community structure is less well known. Here, we relate rates
of gross N mineralisation to fungi-to-bacteria ratios in three natural forest types of contrasting N availability and in a
long-term N-loading experiment in a boreal forest. We report, for the first time, a strong negative correlation between gross
N mineralisation and the fungi-to-bacteria ratio ( = 0.91, P = 0.0005, N = 7). There was also a negative correlation between gross N mineralisation and the C-to-N ratio ( = 0.89, P = 0.001, N = 7), but a weaker positive correlation between gross N mineralisation and soil pH ( = 0.64, P = 0.019, N = 7). Our analysis suggests that soil fungi-to-bacteria and C-to-N ratios are interrelated and that they exert strong influences
on soil N cycling in boreal forests. 相似文献
956.
Eirini I Rigopoulou Maria Mytilinaiou Ourania Romanidou Christos Liaskos George N Dalekos 《Journal of Autoimmune Diseases》2007,4(1):2
Background
Non-organ specific autoantibodies are highly prevalent in patients with chronic hepatitis C (HCV). Among them, anti-liver kidney microsomal type 1 (LKM1) antibody – the serological marker of type 2 autoimmune hepatitis (AIH-2)- is detected in up to 11% of the HCV-infected subjects. On the other hand, anti-liver cytosol type 1 antibodies (anti-LC1) – either in association with anti-LKM1, or in isolation- and anti-soluble liver antigen antibodies (anti-SLA) have been considered as useful and specific diagnostic markers for AIH. However, their specificity for AIH has been questioned by some recent studies, which have shown the detection of anti-LC1 and anti-SLA by immunoprecipitation assays in HCV patients irrespective of their anti-LKM1 status. The aim of the present study was to test the anti-LC1 and anti-SLA presence by specific enzyme linked immunosorbent assays (ELISAs), in a large group of Greek HCV-infected patients with or without anti-LKM1 reactivity as firstly, immunoprecipitation assays are limited to few specialized laboratories worldwide and cannot be used routinely and secondly, to assess whether application of such tests has any relevance in the context of patients with viral hepatitis since antibody detection based on such ELISAs has not been described in detail in large groups of HCV patients.Methods
One hundred and thirty eight consecutive HCV patients (120 anti-LKM1 negative and 18 anti-LKM1 positive) were investigated for the presence of anti-LC1 and anti-SLA by commercial ELISAs. A similar number (120) of chronic hepatitis B virus (HBV) infected patients seronegative for anti-LKM1 was also tested as pathological controls.Results
Six out of 18 (33%) anti-LKMpos/HCVpos patients tested positive for anti-LC1 compared to 1/120 (0.83%) anti-LKMneg/HCVpos patients and 0/120 (0%) of the anti-LKM1neg/HBVpos patients (p < 0.001 for both comparisons). Anti-SLA antibodies were not present in any of the HCV (with or without anti-LKM1) or HBV-infected patients.Conclusion
We showed that anti-LC1 and anti-SLA autoantibodies are not detected by conventional assays in a large group of anti-LKM1 negative patients with chronic hepatitis B and C infections. Based on these results we cannot find any justification for the application of anti-LC1 and anti-SLA tests in the routine laboratory testing of viral hepatitis-related autoantibody serology with the only potential exception being the anti-LC1 screening in anti-LKM1pos/HCVpos patients.957.
Effect of fibers on the flow property of turbulent fiber suspensions in a contraction 总被引:1,自引:0,他引:1
In the flow of turbulent fiber suspensions flowing through a contraction with rectangular cross-section, the Reynolds averaged
Navier-Stokes equation with the term of additional stress resulting from fibers was solved with the Reynolds stress model
to get distributions of the mean velocity, mean pressure, turbulent kinetic energy and turbulent dissipation. It is found
that the mean velocities at exit are small around the center and large near the wall for higher concentration. Fibers reduce
turbulent intensity and turbulent dissipation at central line, but enhance them over the cross section at exit. Fibers have
no effect of restraint on the turbulence in the contraction flow. The additional stress resulting from fibers plays a role
in the increase of drag. 相似文献
958.
Reto M Figueira ME Filipe HM Almeida CM 《Plant foods for human nutrition (Dordrecht, Netherlands)》2007,62(4):139-144
To evaluate the potential benefits and risks associated with tea consumption it is important to identify the constituents
of this beverage. Levels of some minerals, caffeine and catechins in green tea samples commercialized in Portugal were evaluated.
Potassium is the metal present in larger amount (92–151 mg/l). The content of sodium, calcium, fluoride, aluminium, manganese
and iron were 35–69, 1.9–3.5, 0.80–2.0, 1.0–2.2, 0.52–1.9, 0.020–0.128 mg/l, respectively. Chromium and selenium were not
detected. The resulting data showed considerable variability in catechins content. The levels of epigallocatechin gallate
(EGCG) ranged from 117 to 442 mg/l, epicatechin 3-gallate (EGC) from 203 to 471 mg/l, epigallocatechin (ECG) from 16.9 to
150 mg/l, epicatechin (EC) from 25 to 81 mg/l and catechin (C) from 9.03 to 115 mg/l. Caffeine contents in the green tea infusions
studied were between 141–338 mg/l. Green tea infusions provide significant amounts of catechins and could be an important
source of some minerals. 相似文献
959.
Zheng J He J Ji B Li Y Zhang X 《Plant foods for human nutrition (Dordrecht, Netherlands)》2007,62(1):7-11
The root of Platycodon grandiflorum (Jacq.) A. DC has been reported to have a wide range of health benefits in oriental food. This study examined the hypoglycemic
effects of Platycodon grandiflorum (Jacq.) A. DC aqueous-ethanol extract (PGE) in streptozotocin (STZ) -induced diabetic ICR mice (STZ diabetic mice) for the
first time. The effects of PGE on blood glucose, plasma insulin levels and body weight were investigated. A significant decrease
in blood glucose levels was observed after single administration of PGE. Furthermore, Glibenclamide and PGE significantly
suppressed the rise in blood glucose after 30 min in the acute glucose tolerance test. Treatment with glibenclamide and PGE
resulted in a reduction in blood glucose levels from the 2nd week, and this reduction was maintained until the 4th week of
treatment. The body weight changed slightly in glibenclamide and PGE treated mice in comparison with the STZ control group.
Plasma insulin levels were increased with glibenclamide treatment in STZ diabetic mice, whereas such effect was not observed
with PGE. These results indicated that PGE could induce hypoglycemic effects without stimulating insulin secretion. 相似文献
960.
Bryszewska MA Ambroziak W Langford NJ Baxter MJ Colyer A Lewis DJ 《Plant foods for human nutrition (Dordrecht, Netherlands)》2007,62(3):121-126
The potential of selenium-enriched rye/wheat sourdough bread as a route for supplementing dietary selenium intakes is reported.
In addition to their normal diets, 24 female volunteers (24 to 25 years old) were fed either selenium-enriched bread or non-enriched
bread each day (68.02 and 0.84 μg selenium day−1 respectively) for 4 weeks. The chemical form of the selenium in the bread had been characterised using HPLC-ICP-MS, which
showed that 42% of the extractable selenium was present as selenomethionine. Plasma selenium levels and plasma platelet glutathione
peroxidase (GPx1) activity were measured in the volunteers’ blood over a 6-week period. A statistically significant difference
(p = 0.001) was observed in the mean percentage change data, calculated from the plasma selenium level measurements for the
enriched and control group, over the duration of the study. A comparable difference was not observed for the platelet GPx1
activity (p = 0.756), over the same period. Two weeks after cessation of the feeding stage, i.e., at t = 6 weeks, the mean percentage change value for the selenium plasma levels in the enriched group was still significantly
elevated, suggesting that the absorbed selenium had been incorporated into the body’s selenium reserves, and was then being
slowly released back into the volunteers’ blood. 相似文献