Effects on animal performance and sward composition of mixed and sequential grazing of permanent pasture by cattle and sheep     

M.D. Fraser  D.A. Davies  J.E. Vale  W.M. Hirst  I.A. Wright 《Livestock Science》2007,110(3):251-266

Previous experiments have shown that mixed or conjoint grazing, when two or more animal species are grazed together, can lead to improved performance of one or more of the species and a higher total output per unit area. Sequential grazing systems, when different animal species graze an area in succession, also have the potential to improve productivity. This experiment directly compared these two approaches for integrating the grazing of cattle and sheep when pastured on improved permanent pasture. Four treatments were compared: 1) sheep only from May to October (S/S); 2) cattle only from May to July followed by sheep only from August to October (C/S); 3) cattle and sheep from May to July, sheep only for the rest of the growing season (C + S/S); and 4) cattle and sheep from May to October (C + S/C + S). Each treatment was replicated three times. From May until weaning at the end of July the plots were grazed by steers and ewes and lambs, and from weaning until October by steers and lambs. Sward heights were maintained at 6 cm using a “put and take” stocking system. Animal performance and sward composition data were collected during three growing seasons, 2001–2003. During the pre-weaning period lambs grazing plots which were grazed only by sheep had significantly poorer growth rates than those grazing plots where there was mixed grazing. Lambs grazing the sheep only plots also had lower liveweight gain during the post-weaning period, with the highest growth rates being recorded on the C + S/C + S treatment. Carrying capacity and total liveweight gain per unit area post-weaning were also consistently higher for the C + S/C + S treatment, while carrying capacity pre-weaning was highest for the C/S treatment. Measurements of clover content in the grazed horizon and botanical separation of material from quadrat cuts indicated that even under relatively controlled conditions choice of grazing system can influence sward composition. However, there was no clear link between any single sward change and the growth of the animals, indicating that the improved performance of cattle and sheep under mixed grazing is the result of a combination of factors, rather than a response to a particular sward parameter.  相似文献   

Maintaining estuary quality for shorebirds: towards simple guidelines     

Andrew D. West  John D. Goss-Custard  Richard A. Stillman 《Biological conservation》2005,123(2):211-224

It is increasingly important to be able to monitor and maintain the quality of estuaries for overwintering shorebirds. Bird numbers alone are not sufficient to indicate quality nor, as recent research shows, can it be assumed that site quality is being maintained simply because there is enough food to meet the birds’ physiological demands; i.e., the amount of food available per bird in autumn needs to be greater than the amount eaten. But how much greater? We used a simple individuals-based and behaviour-based model to explore the factors that affect the relationship between overwinter mortality and the amount of food available per bird in autumn (the food:bird ratio). The aims were to explore how the natural history characteristics of a shorebird species affected the shape of this relationship, in order to identify characteristics of the system that should be included in any monitoring programme of site quality. In all cases there was a minimum threshold food:bird ratio above which mortality did not vary and below which mortality increased steadily. The amount of food per bird required at the threshold varied from one to six times the amount actually consumed by each bird during winter, depending on the amount of realism included in the model. The minimum threshold ratio was most strongly influenced by the shape of the relationship between intake rate and prey density - the functional response - and, when interference competition occurred, by the distribution of the birds’ main food supply. Simulations with realistic spatial distributions of prey predicted that the minimum required amount of food per bird would be between two and five times the amount actually consumed. The threshold approach could provide a simple method of monitoring estuary quality based on food supply and bird numbers. It also provides a potentially clearly-defined and unambiguous measure of the carrying capacity of a site. If applied to a sufficient number of real estuaries, general guidelines for maintaining estuary quality based on estuary characteristics, food supply and bird species might be established.  相似文献   

区域水资源承载力的主成分分析法及应用——以陕西省西安市为例   总被引：3，自引：1，他引：3  

邵金花  刘贤赵 《安徽农业科学》2006,34(19):5017-5018,5021

运用主成分分析法对区域水资源承载力进行分析评价,评价结果客观地反映了西安市及各区的水资源开发利用状况。通过与模糊综合评判法的结果进行对比分析,进一步证实主成分分析法的合理性和科学性,为区域水资源承载力的综合评价提供参考依据。  相似文献   

八一农大理化楼的地基处理     

王晖  王海波 《黑龙江八一农垦大学学报》1999,11(1):48-50

本文以八一农大理化楼工程实践为例,介绍用坑探弥补钻探所取数据的不足,有效的提高了地基土的设计承载能力,从而降低了工程造价。这种方法对同类工程十分有用。  相似文献   

便携式应急移动中继通信系统的野外试验研究     

李丹丹  李存宇  张景忠  蔡志勇  孙少辉  王立峰 《林业科技》2009,34(5):32-35

利用改进后的便携式应急移动调频中继通信系统的两种组网方式,采取人员背负、嘹望台架设、车载和机载四种中继台搭载方式,开展了地面和机载应急中继组网通信试验,测试了通信效果和通信距离等综合技术参数,并对通信情况进行了分析,全面检验了该系统在山地林区进行应急移动中继通信组网的能力。  相似文献   

湛江市大气环境承载力与环境安全研究   总被引：1，自引：0，他引：1  

鲁磊  郑宇涛 《安徽农业科学》2011,39(15):9144-9146

通过建立大气环境承载力量化模型,对湛江市2007年大气环境承载状态进行了现状评价,并对湛江市2010年和2020年大气环境承载状态进行了情景预测研究。结果表明,湛江市大气环境承载现状良好,但是在经济快速增长、城市化加快的大背景下,如果湛江继续按照现有模式发展,到2020年大气环境承载将达到预警状态。  相似文献   

宁夏红寺堡区水资源承载能力分析与研究     

王志清  戴映辉 《安徽农业科学》2011,39(32):19958-19960

分析了宁夏红寺堡区当地水资源、扬黄水资源、可利用水资源的状况和用水现状。结合红寺堡区发展规划,在大力推广节水灌溉技术应用、种植结构调整、节水工程改造、节水灌溉制度应用的前提下,挖掘灌区用水潜力;设定区域用水水平,预测区域在2015年工业、农业、人畜、新增项目用水需求,分析区域水资源可利用量与用水需求的关系,评价区域水资源承载能力,为区域发展决策者提供参考。  相似文献   

基于因子分析和熵权法的赣江源流域水资源承载力研究   总被引：1，自引：1，他引：0  

刘慧  蔡定建  许宝泉  余长林 《安徽农业科学》2011,39(23):14264-14267,14277

以赣江源流域地区为例,运用因子分析法,从经济社会、生态环境、自然水资源和人口现状等16个指标中筛选出影响该区水资源承载力变化的4个主因子C1、C2、C3、C4,并通过熵权法对4个因子的得分赋权重,综合评价出2001～2009年该源流域水资源承载力的状况。结果表明,近10年来,该区域水资源承载力总体走向一个相对健康的方向。通过对赣江源流域水资源利用现状的分析,从水量分配、水权归属及产业结构优化等方面提出提高水资源承载能力的措施,以期为该区域经济社会发展规划和生态环境保护战略的制定,寻求可持续发展模式提供水资源承载信息的参考和保障。  相似文献   

山西省不同资源型地区生态足迹及可持续发展评价          下载免费PDF全文

杜娟 《农学学报》2011,(3)

通过聚类分析,将山西的119个县区按照资源的属性,分成矿产资源型地区、农业资源型地区、综合资源型地区、资源匮乏型地区、特色资源型地区等5类不同资源型地区,选取有代表性的县市区作为研究对象,应用生态足迹模型分析其生态经济系统可持续发展状况。结果表明,可持续性石楼县(资源匮乏型地区)>河津市(特色资源型地区)>太谷县(农业资源型地区)>榆次区(综合资源型地区)>盂县(矿产资源型地区),并针对各区域的特点提出相应的转型对策。  相似文献   

内陆水域负载量研究     

陈朋 《安徽农业科学》2010,38(33):18955-18956,18978

综述了内陆水域水产养殖负载量的研究概况,并对各种研究方法的优点和局限性进行了评价,最后对负载量的研究前景进行了展望。  相似文献