家庭生态农场的氮素营养生产分析

引言土地的沙漠化也许是人类文明进程所付出的最沉重代价。我国北方干旱地区是一个巨大的潜在“沙漠化温床”,巳沙化土地达3.34×     

Prospects for genetically modified crops

Genetically modified (GM) crops have been in use commercially around the world for almost a decade. This review covers the successes and failures of GM crop varieties in that time, the current status of GM crop adoption and the traits that are being used. It also describes some of the GM crops that might come on to the market in the next decade. The barriers in the way of GM crop development in Europe, including consumer hostility, the difficulty in gaining official approval and discriminatory labelling laws are discussed.     

华北平原种养一体规模化农场氮素流动特征及利用效率——以河北津龙循环农业园区为例

种养一体规模化、集约化是华北平原农业发展的必然趋势,而氮素是连接种植养殖的主要养分资源,以河北津龙循环农业园区为例,采用文献资料、实地调查方法分析农场水平氮素流动特征及利用率,并通过情景分析方法提出农场氮素管理措施,为实现农场水平氮养分资源高效利用、提高农场生产系统生产力和改善华北平原循环农业模式提供技术支撑和科学依据.结果表明: 在农场水平下,化肥和有机肥输入氮量674.6 kg·hm^-2·a^-1,占总输入氮量的88.3%,氮利用率为41.5%,种植系统氮盈余量190.7 kg·hm^-2·a^-1,施氮量过多是造成种植系统氮利用率低和氮素盈余量高的主要原因.养殖系统中外购饲料提供氮量占饲料总输入氮量的83.2%,粪尿排氮量为776.6 t·a^-1,而还田比例仅为36.3%,氮利用率19.7%.农场水平氮总利用率为40.7%.情景分析表明,农田减少化肥施氮量50%(情景1)、增加来自农场内部玉米籽粒产量(情景2)措施,可分别使种植系统氮利用率提高34.6%和15.6%,同时农场水平氮总利用率分别提高18.7%和9.8%;另外,优化养殖系统饲料结构(情景3),可使氮总利用率提高19.1%.因此,减少化肥氮施用量、调整作物种植结构、优化饲料结构等,是提高农场氮生产力和实现环境友好双赢效果的措施和途径.     

A Comprehensive Energy and Economic Assessment of Biofuels: When “Green” Is Not Enough

Referee: Dr. Charles A. S. Hall, Department of Environmental Studies, State University of New York, College of Environmental Science and Forestry, 1 Forestry Drive, Syracuse, NY 13210 Biofuel production systems are sometimes claimed to be able to fill in for future fossil fuel shortages as well as to decrease carbon dioxide emissions and global warming. As such, they are often promoted as a “green” alternative to fossil fuels. I present a comprehensive, system-based case study of biofuel production from maize or corn (Zea mays L.) and evaluate it critically in this review. The case study is taken as an example of the comprehensive approach that I suggest for any energy crop. I conclude that the biofuel option on a large scale is not a viable alternative based on economic, energy and eMergy (amount of available energy [exergy] of one form [usually solar] that is directly or indirectly required to provide a given flow or storage of exergy or matter) analyses of the case study data and estimated possible improvement of yield and efficiency. This is true for developed countries due to their huge energy demand compared with what biofuel options are able to supply as well as for developing countries due to the low yield of their agriculture and competition for land and water for food production. However, biofuels may contribute to optimizing the energy and resource balance of agricultural, livestock, or industrial production systems at an appropriate scale. I present a proposal to integrate ethanol production with industrial activities within a “zero emission framework” as a suggestion for optimization strategies capable of making the biofuel option more sustainable and profitable in those cases where it is appropriate.     

Emission Estimates of Particulate PAHs from Biomass Fuels Used in Delhi,India

The emission factors for particulate-phase polycyclic aromatic hydrocarbons (PAHs) were evaluated for various biomass fuels (fuelwood, dung cakes, and agricultural residue) that are being commonly used in Delhi as a source of energy. Emission factors of total particulate PAHs varied from 35.9 ± 1.9 to 59.7 ± 4.4 mg/kg. Higher levels of total PAHs and particulate matter (PM) were found from dung cakes as compared to fuelwood and agricultural residue. The emission factors for PM from dung cake, fuelwood, and agricultural residue are 25 ± 8, 15 ± 3.2, and 12.1 ± 9.4 g/kg, respectively. The total PAH emissions showed an increase with high particulate matter emission rates and lower combustion efficiency. Fluoranthene, pyrene, benzo[a]anthracene, chrysene, benzo[b]fluoranthene, and benzo[a]pyrene constituted the major fraction of PAH emissions from all biomass fuels. The annual budget estimates (total emissions per year) for PAHs and PM from biomass fuels used in Delhi are 30.5 ± 2.3 Mg (Megagrams) and 11.6 ± 4.4 Gg (Gigagrams), respectively. An attempt has also been made to evaluate the preliminary budget estimates of PAHs and PM emitted from the use of biomass fuels as a source of energy in India by using the emission factors obtained in the present study.     

Managing the transition from purebred to rotational crossbred dairy cattle herds: three technical pathways from a retrospective case-study analysis

The growing interest in rotational crossbreeding in Western countries is due to its potential to improve reproductive and health performances of cows. Although a large amount of research focuses on assessing crossbred cows’ performances, how to manage the transition from purebred to rotational crossbred herds is under-explored. Based on a retrospective analysis of French dairy herd case studies, we aimed to identify and characterise technical pathways to make such a transition. In 2018, we performed semi-directive interviews on 26 commercial dairy farms. Data were collected to describe changes in breeding, replacement and culling management practices from the first crossbred mating with purebred cows to the management of a mainly crossbred herd in 2018. Based on a multivariate analysis, we identified two main guidelines structuring technical pathways to move towards rotational crossbred herds: (i) the depth and scale of change (i.e. farm v. herd) associated with the introduction of rotational crossbreeding in the whole-farm dynamics and (ii) the changes in herd replacement and breeding practices to adapt to the evolution of herd demographics induced by the evolution of the dairy crossbred mating rate over time (high from the beginning v. distributed over time). Hierarchical clustering discriminated three groups of farmers differing in their technical pathway to move towards a rotational crossbred herd. In pathway 1, farmers customised one or several rotational crossbreeding schemes to support whole-farm transition towards an organic or grass-based system. Once the scheme stabilised, they quickly implemented it and had to readjust replacement and culling practices to regulate imbalance in herd demographics induced by the improvement in cow fertility. In pathway 2, farmers also customised one or several rotational crossbreeding schemes to support whole-farm redesign but they implemented it more gradually in the herd, which induced no major imbalance in herd demographics. In pathway 3, farmers predefined a relatively well-known rotational crossbreeding scheme to correct fertility issues of purebred cows without any changes at the farm level. They implemented it quickly from the beginning and had to adapt herd replacement and culling to regulate imbalance in herd demographics induced by the improvement in cow fertility. These first empirical evidences on how dairy farmers manage the transition from a purebred to rotational crossbred herd provide original scientific and operational contributions.     

Life Cycle Assessment of Offshore Wind Farm Siting: Effects of Locational Factors,Lake Depth,and Distance from Shore

According to previous studies, the life cycle energy intensity of an offshore wind farm (OWF) varies between 0.03 and 0.13 megawatt‐hours (MWh) of primary energy for each MWh of electricity generated. The variation in these life cycle energy intensity studies, after normalizing for capacity factor and life span, is significantly affected by OWF location because of geographical properties, namely, wind speed and water depth. To improve OWF siting, this study investigates how an OWF's distance from shore and geographical location impacts its environmental benefit. A process‐based life cycle assessment is conducted to compare 20 OWF siting scenarios in Michigan's Great Lakes for their cumulative fossil energy demand, global warming potential, and acidification potential. Each scenario (four lake locations at five offshore distances) has unique foundation, transmission, installation, and operational requirements based on site characteristics. The results demonstrate that the cumulative environmental burden from an OWF is most significantly affected by (1) water depth, (2) distance from shore, and (3) distance to power grid, in descending order of importance, if all other site‐relevant variables are held constant. The results also show that when OWFs are sited further offshore, the benefit of increased wind energy generation does not necessarily outweigh the increase in negative environmental impacts. This suggests that siting OWF nearer to shore may result in a better life cycle environmental performance. Finally, we demonstrate how much an OWF's environmental burdens can be reduced if the OWF system is either recycled, transported a shorter distance, or manufactured in a region with a high degree of renewable energy on the grid.     

Cultivation of Microalgae in Dairy Farm Wastewater Without Sterilization

The present study investigated the feasibility of cultivating microalgae in dairy farm wastewater. The growth of microalgae and the removal rate of the nutrient from the wastewater were examined. The wastewater was diluted 20, 10 and 5 times before applied to cultivate microalgae. A 5 dilution yielded 0.86 g/L dry weight in 6 days with a relative growth rate of 0.28 d^?1, the 10× dilution gave 0.74 g/L and a relative growth rate of 0.26 d^?1 while the 20× dilution 0.59 g/L and a relative growth rate 0.23 d^?1. The nutrients in the wastewater could be removed effectively in different diluted dairy wastewater. The greatest dilution (20×) showed the removal rates: ammonia, 99.26%; P, 89.92%; COD, 84.18%. A 10× dilution removal% was: ammonia 93; P 91 and COD 88. The 5× dilution removal% was: ammonia 83; P 92; COD 90.