Cover crop evapotranspiration under semi-arid conditions using FAO dual crop coefficient method with water stress compensation     

G. Bodner  W. Loiskandl 《Agricultural Water Management》2007,93(3):85-98

Cover cropping is a common agro-environmental tool for soil and groundwater protection. In water limited environments, knowledge about additional water extraction by cover crop plants compared to a bare soil is required for a sustainable management strategy. Estimates obtained by the FAO dual crop coefficient method, compared to water balance-based data of actual evapotranspiration, were used to assess the risk of soil water depletion by four cover crop species (phacelia, hairy vetch, rye, mustard) compared to a fallow control. A water stress compensation function was developed for this model to account for additional water uptake from deeper soil layers under dry conditions. The average deviation of modelled cumulative evapotranspiration from the measured values was 1.4% under wet conditions in 2004 and 6.7% under dry conditions in 2005. Water stress compensation was suggested for rye and mustard, improving substantially the model estimates. Dry conditions during full cover crop growth resulted in water losses exceeding fallow by a maximum of +15.8% for rye, while no substantially higher water losses to the atmosphere were found in case of evenly distributed rainfall during the plant vegetation period with evaporation and transpiration concentrated in the upper soil layer. Generally the potential of cover crop induced water storage depletion was limited due to the low evaporative demand when plants achieved maximum growth. These results in a transpiration efficiency being highest for phacelia (5.1 g m⁻² mm⁻¹) and vetch (5.4 g m⁻² mm⁻¹) and substantially lower for rye (2.9 g m⁻² mm⁻¹) and mustard (2.8 g m⁻² mm⁻¹). Taking into account total evapotranspiration losses, mustard performed substantially better. The integration of stress compensation into the FAO crop coefficient approach provided reliable estimates of water losses under dry conditions. Cover crop species reducing the high evaporation potential from a bare soil surface in late summer by a fast canopy coverage during early development stages were considered most suitable in a sustainable cover crop management for water limited environments.  相似文献   

Measuring versus estimating net radiation and soil heat flux: Impact on Penman–Monteith reference ET estimates in semiarid regions     

Pedro Gavilán  Joaquín Berengena  Richard G. Allen 《Agricultural Water Management》2007

The standardized ASCE Penman–Monteith and FAO-56 equations were used to estimate reference evapotranspiration (ET₀) using estimated and measured net radiation (R_n) and soil heat flux (G), based on hourly and daily meteorological data. The estimates were evaluated against lysimeter measurements. The results indicate that using measured or estimated values of R_n and G can have significant effect on the accuracy of the ET₀ estimations, especially when calculations were made on an hourly basis. The FAO-56 version performed very well during the irrigation season on a daily basis. The use of measured R_n and G did not improve ET₀ estimation on a daily basis, therefore, the use of estimated R_n and G appears to be dependable when calculations are based on 24-h weather data. When daily ET₀ was calculated from hourly estimations, the results were different depending on the version used. The ASCE version was more accurate, especially when R_n and G were measured. Therefore, measurement of R_n and G may have potential to improve estimation only when daily ET₀ is calculated from hourly estimations. The PM FAO-56 version was always a little less accurate than the ASCE version. For hourly calculations, using a constant surface resistance (as in FAO-56 version), the PM method underpredicted for high evaporative demand and vice versa. The ASCE version performed better than PM FAO-56 version when R_n and G were measured and estimated. Therefore, ASCE version tended to provide quite accurate values of hourly ET₀, even using estimated values of R_n and G. As conclusion, the methods proposed by FAO-56 for estimating R_n and G tended to produce accurate estimates for daily and hourly ET₀ under semiarid conditions and can be used with some degree of confidence for estimating ET₀. In addition, results suggest that the ASCE standardized equation on an hourly basis improved the accuracy of ET₀ estimation with respect to the FAO-56 version.  相似文献   

Simple method for synthesizing phenolicβ-O-4 dilignols     

Shingo Kawai  Kyoko Okita  Kazuhiro Sugishita  Ai Tanaka  Hideo Ohash 《Journal of Wood Science》1999,45(5):440-443

A modified synthetic method for phenolic-O-4 lignin substructure model dimers was developed involving protection of the phenolic hydroxyl group of acetophenons with benzoyl chloride, bromination with 4-dimethylaminopyridiniumbromide perbromide, condensation with phenols in the presence of 18-crown-6-ether, condensation with paraformaldehyde, reduction with NaBH₄ and debenzoylation. This method results in shorter reaction times and increasing yields without the application of strict anhydrous and drastic conditions or chloric solvents. This alternative route could be applied to the-O-4 dilignol syntheses of four combinations of guaiacyl and syringyl derivatives.  相似文献   

Exotic species,fisheries and conservation of freshwater biodiversity in tropical Asia: the case of the Sepik River,Papua New Guinea     

David Dudgeon  Ross E. W. Smith 《水产资源保护:海洋与淡水生态系统》2006,16(2):203-215

1. Development of effective conservation strategies for freshwater biodiversity must take account of the trade‐off between species preservation and human use of ecosystem goods and services. The latter cannot be prevented, and attempts to manage ecosystems that focus solely on maximizing biodiversity will fail. 2. A compromise position of management for ecosystem functioning and human livelihoods — rather than preservation of every species — will provide a better basis for biodiversity conservation. This has implications for the management of exotic species. 3. There are some situations, in lentic habitats in Sri Lanka, for example, where the establishment of exotics has increased fishery yields without apparent detriment to native biodiversity. The Sepik River in Papua New Guinea provides another illustration of potential compromises between human livelihoods and biodiversity conservation. 4. The Sepik supports a relatively unproductive fishery. Two fish stocking projects (in 1987–93 and 1993–97), representing a partnership between the Papua New Guinea Government and the United Nations (UNDP/FAO), led to the introduction of a suite of exotic fish into the Sepik. Species were selected on the basis of their potential to occupy niches not filled by native fish. Unfortunately, the outcomes of these introductions are poorly documented, although there is preliminary evidence both of increased human use of exotic fish as well as declines of some native species associated with the spread of exotics. 5. Better understanding of the results of the Sepik fish introductions is important, because the pressures of burgeoning human populations in most of tropical Asia make it impossible to preserve near‐pristine environments such as the Sepik. While attempts to conserve natural or near‐natural systems must remain a priority, there is a need to develop strategies for the management of damaged or degraded ecosystems, which may contain exotics, with the aim of maintaining ecosystem functioning and, if possible, maximizing the persistence of native biodiversity. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

利用不亲和野生种育成花生新品种花育56号     

王传堂  高华援  王秀贞  唐月异  吴琪  孙全喜  杨珍  胡东青  徐建芝  刘海龙 《花生学报》2014,(2):62-64

花育56号,原代号09-测S8,系采用花生不亲和野生种Arachis glabrata Benth作父本、栽培种四粒红为母本杂交,通过果针离体培养获得可育杂种,选取F2优良单株与栽培品种花37回交,经系谱法选育而成的珍珠豆型花生新品种。2013年通过安徽省品种鉴定(皖品鉴登字第1205004),2014年通过吉林省品种登记(吉登花生2014002)。  相似文献   

Accessing genetic resources: international law establishes multilateral system     

Cary Fowler 《Genetic Resources and Crop Evolution》2004,51(6):609-620

The International Treaty on Plant Genetic Resources for Food and Agriculture is rapidly gathering sufficient ratifications to become international law. Once it enters into force, it will define the rules for access and benefit-sharing associated with most genetic resources of major food crops. This paper explains how the new Multilateral System established by the Treaty will work, and points out a number of ambiguities and problems in the text. Despite these shortcomings, the Treaty provides the international community of researchers, plant breeders, and farmers with an opportunity to foster cooperation and further the conservation and use of plant genetic resources.  相似文献   

FAO可持续土地资源管理综合规划指南及启示     

温占军  晏晓红  耿冯康  殷少美 《农业工程学报》2005,21(13):142-145

土地资源可持续利用是基于可持续发展的核心内容——资源的可持续利用而形成的，指对人类生存所依赖的物质资源，在追求经济效益最大的同时，维持和改善土地资源的生产条件和环境基础。在当前社会主义市场经济体制下,可持续土地资源管理的任务主要依靠政府严格的土地利用规划事先调节和控制，引导、限制或鼓励人们的土地利用行为，保证土地资源的合理配置和可持续利用。该文试图在分析FAO的土地规划的概念、内容、体系、成功的关键因素、及编制的步骤和方法基础上，展开探讨并对完善我国土地利用规划提出了借鉴意义。  相似文献   

联合国粮食及农业组织网上资源简介     

杨玉花 《农业图书情报学刊》2007,19(3):93-94

在经济全球化和信息化的背景下,世界农业的信息资源日益电子化和网络化。本文拟就联合国粮农组织网上资源的主要内容和检索作一分析。  相似文献   

东北丘陵半干旱区参考作物蒸散量计算方法比较     

张和喜  迟道才  尹光华  刘作新  王晓瑜 《安徽农业科学》2007,35(3):636-638,640

利用FAO Penman-Monteith公式、FAO Penman修正式和Priestley-Taylor公式对东北丘陵半干旱区观测到的气象数据进行了逐日参考作物蒸散量计算.结果显示,FAO Penman修正式的计算值比FAO Penman-Monteith公式的计算值平均偏大约16%,2种比较方法具有很好的相关性;而Priestley-Taylor公式的计算值与FAO Penman-Monteith公式的计算值相比,差异比较显著,是由于Priestley-Taylor公式没有考虑空气动力项对参考作物蒸散量的影响.因此,在东北丘陵半干旱区使用Priestley-Taylor公式计算参考作物蒸散量,必须根据不同月份对公式中的常数项重新进行修正.  相似文献   

内蒙古河套灌区主要粮油作物系数的确定   总被引：4，自引：0，他引：4  

戴佳信  史海滨  田德龙  夏玉红  李茂华 《灌溉排水学报》2011,30(3)

根据FAO-56作物需水量指南推荐的作物系数计算方法,分别计算内蒙古河套灌区磴口试验站小麦、玉米(覆膜与未覆膜)、油料向日葵3种作物的单、双值作物系数。结果表明,磴口试验站单值作物系数较双值作物系数值计算的ET值偏低,双值作物系数计算的ET值与实测结果更为接近,验证了双值作物系数在河套灌区的适用性。  相似文献