豆科牧草研究进展

豆科牧草的属间、属内、种间与种内均存在着巨大的遗传变异，利用这种变异，通过育种与选择，已培育出可良好地适应广泛的环境与管理条件的品种，遗传操作为此提供了更为广阔的空间，在豆科牧草固氮方面，对固氮过程、氮向伴生禾草的传送途径及残余氮对后继农作物的价值均有了进一步的理解。对包括施氮、采摘策略和影响混播草地中禾本科－豆科牧草平衡的胁迫等相互作用因素均已给予了阐明。在禾草／白三叶草草地为基础的家畜生产系统中，氮素的损失及其对环境产生的不良作用低于大量施氮的禾草草地系统。与禾草相比，豆科牧草无是用作放牧、青贮或用作干草，其物理、化学和解剖学等方面的特性均可增加家畜的嗜食性和自由采食量。由于豆科牧草的营养价值、可利用营养成分和采食特征，在单一豆科牧草或豆科牧草比重较大的禾草－豆科牧草混播草地上采食的不同种类、不同类型家畜的个体生产性能均优于在禾草草地上采食者。值得注意的是浓缩单宁在动物营养中的有益作用，这类单宁存在于诸如百脉根（Lotus corniculatus）、红豆草（Onobrychis viciifolia）和冠状岩黄芪（Hedys-crum coroharium）等植物中，其防止家畜患膨胀病，通过使较多的氨态氮到达小肠而提高氮的利用，并减轻绵羊肠道中线虫的作用。显然，培育含浓缩单宁的转基因豆科牧草是植物育种者现阶段的主要目标之一。此外，豆科牧草亦有许多其他用途，例如，在葡萄园中用作保护性植被，禾谷类作物的下层植被和为制药业提供次生化合物等。豆科牧草以其植物多态性和花朵的颜色等亦在美化景观和自然保护区中发挥着作用。可以预见，豆科牧草的作用在温带可持续农业中的作用将会增加，充分发掘现有的知识和相关研究成果，及有效的技术将是未来豆科牧草利用的主要特色。

Advances in Forage Legume Technology

Breeding and selection within the vast pool of genetic variability that exists among and within the species of different genera of forage legumes have led to cultivars that are well adapted to a wide range of environmental and management conditions; genetic manipulation techniques offer further scope. There is increased understanding of the N 2?fixation process, the routes of N transfer to associated grasses and the residual N value to subsequent arable crops. The interacting factors that include fertiliser N, defoliation strategies and stresses for example, and which govern the grass?legume balance in mixed associations, have been elucidated. Nitrogen losses with their adverse effects on the environment are lower in animal production systems based on grass/white clover than on highly N?fertilised grass swards. The physical, chemical and anatomical features of forage legumes, whether utilised as grazing, silage or hay, all contribute to enhanced acceptability and voluntary food intake compared with grasses. The net result of the legume nutritive value, nutrient availability and intake characteristics is superior individual animal performance from different types and classes of livestock fed on legume monocultures or legume?rich grass?legume mixtures relative to being fed on grass. A notable finding is the beneficial role in animal nutrition of condensed tannins, present in Lotus corniculatus, Onobrychis viciifolia and Hedysarum coronarium for instance; these tannins prevent bloat in livestock, improve N utilisation through more non?ammonia N reaching the small intestine, and alleviate the effects of intestinal nematodes in sheep. The development of transgenic legumes containing condensed tannins is clearly a major objective for plant breeders. A number of alternative uses for forage legumes has been identified that include protective vegetation in vineyards, a living understorey for cereals, and provision of secondary compounds for the pharmaceutical industry for example. With their plant diversity and palette of flower colours, forage legumes contribute to landscape beauty and to nature conservation. It is foreseen that the role of forage legumes in sustainable farming in temperate climes will increase. Exploitation of existing knowledge, relevant research and development, and effective technology transfer will all feature.