Using drainage systems for supplementary irrigation

The use of drainage systems for supplementary irrigation is widespread in The Netherlands. One of the operating policies is to raise the surface water level during the growing season in order to reduce drainage (water conservation) or to create subsurface irrigation. This type of operation is based on practical experience, which can be far from optimal.To obtain better founded operational water management rules a total soil water/surface water model was built. In a case study the effects of using the drainage system in a dual-purpose manner on the arable crop production were simulated with the model. Also, the operational rules for managing this type of dual-purpose drainage systems were derived.The average annual simulated increase in crop transpiration due to water conservation and water supply for subsurface irrigation are 6.0 and 5.4 mm.y^–1, respectively. This is equivalent with 520 × 10³ and 460 × 10³ Dfl.y^–1 for the pilot region (2 Dfl 1 US $). The corresponding investments and operational costs are 600 × 10³ Dfl and 9 × 10³ Dfl.y^–1 for water conservation and 3200 × 10³ Dfl and 128 × 10³ Dfl.y^–1 for subsurface irrigation. Hence, water conservation is economically very profitable, whereas subsurface irrigation is less attractive.Comparing the management according to the model with current practice in a water-board during 1983 and 1986 learned that benefits can increase with some 50 and 500 Dfl per ha per year, respectively.     

A global benchmark map of water productivity for rainfed and irrigated wheat

The growing pressure on fresh water resources demands that agriculture becomes more productive with its current water use. Increasing water productivity is an often cited solution, though the current levels of water productivity are not systematically mapped. A global map of water productivity helps to identify where water resources are productively used, and identifies places where improvements are possible. The WATPRO water productivity model for wheat, using remote sensing data products as input, was applied at a global scale with global data sets of the NDVI and surface albedo to benchmark water productivity of wheat for the beginning of this millennium. Time profiles of the NDVI were used to determine the time frame from crop establishment to harvest on a pixel basis, which was considered the modelling period. It was found that water productivity varies from approximately 0.2 to 1.8 kg of harvestable wheat per cubic metre of water consumed. From the 10 largest producers of wheat, France and Germany score the highest country average water productivity of 1.42 and 1.35 kg m⁻³, respectively. The results were compared with modelling information by Liu et al. (2007) who applied the GEPIC model at a global scale to map water productivity, and by Chapagain and Hoekstra (2004) who used FAO statistics to determine water productivity per country. A comparison with Liu et al. showed a good correlation for most countries, but the correlation with the results by Chapagain and Hoekstra was less obvious. The global patterns of the water productivity map were compared with global data sets of precipitation and reference evapotranspiration to determine the impact of climate and of water availability reflected by precipitation. It appears that the highest levels of water productivity are to be expected in temperate climates with high precipitation. Due to its non-linear relationship with precipitation, it is expected that large gains in water productivity can be made with in situ rain water harvesting or supplemental irrigation in dry areas with low seasonal precipitation. A full understanding of the spatial patterns by country or river basin will support decisions on where to invest and what measures to take to make agriculture more water productive.     

An empirical cohort model for management of Terra Firme forests in the Brazilian Amazon

A model to project forest growth in the Terra Firme forests of the eastern Amazon is described. It is based on 12–17 years measurements from experimental plots at Jarí and Tapajós. Forest stands are represented by cohorts of species group, diameter, and defect. There are 54 species groups, with a robust diameter increment function fitted to each, tables of mortality by crown and defect status, and recruit lists by disturbance level and locality. Stand level functions partition trees by crown status, and modify growth for stand density. Recruitment is a function of basal-area losses. Evaluation compares model performance with two experiments involving heavy felling in Tapajos State Forest. At one site, total bole volume growth of all species over 45 cm DBH was 2.56 m³ ha⁻¹ year⁻¹ over 17 years, whereas the model projected 3.13 m³ ha⁻¹ year⁻¹. At the other site, actual growth over 12 years was 0.39 m³ ha⁻¹ year⁻¹, with the model giving an identical result. Both felled and control plots are compared in the study and accurately simulated. Some weaknesses in the model are discussed.     

基于主题图的农业模型描述与表示方法

为了提升不同学科模型资源的共享与管理能力,提出了一种新的农业模型描述与表示方法。它以模型组件描述信息为元数据来生成不同层次主题图。首先分析农业模型特征,建立农业模型与模型组件之间的映射关系;然后,抽取农业模型组件刻面与关联描述信息,构建了农业模型组件描述模型（DM-AMC）,进一步将DM-AMC表示为主题类型、关联类型、事件类型以及关联角色;最后,通过实例化并采用匹配融合算法生成了面向农业模型组件的主题图（TM-AMC）。研究以作物生育期模型为例,生成了统一描述与可动态扩展的原子主题图XTM文档。通过对农业模型信息的统一描述,并以DM-AMC为基础生成多层次、便于统一访问的TM-AMC,可提升农业模型信息的全局共享与管理能力。     

从文献分析看我国白芨研究进展

 利用《中文科技期刊全文数据库》等检索工具,采用文献计量法,对我国1975～2008年学术刊物上发表的白芨研究文献进行统计分析,研究年发文量、合作度、合作率、期刊分布、研究单位等指标和内容,定量分析出我国白芨研究的主要人物、研究领域、研究单位及现状,明确了各年研究的重点、热点、核心人物和主要机构,以期对我国白芨研究有全面的了解,这对白芨的进一步研究和学科的发展有重要的指导作用。