Abstract: A study comparing water use efficiency and root biomass/shoot biomass ratio of Alfalfa and Astragalus adsurgens at seedling stage in growth chambers with two levels of soil water content treatment shows that the instantaneous leaf WUE of Aa is higher than that of Alfalfa at each growing stage with accorded soil water content.The root biomass/shoot biomass and root length/plant height of Aa are also much fuller than those of Alfalfa,more particularly,even a low level soil water treatment,alfalfa yields larger biomass with a higher per unit water consumption rate and decreases biomass growth with the decrease of soil water content.Consequently,Alfalfa exhibits a high transpiration rate as well as a high rate of root extension,resulting in quick soil water consumption.Generally,high soil water content effects the productive efficiency of Alfalfa.As for Aa,however,the variable soil water content does not affect its growth significantly.Based on the year-on-year research data and the undulating land condition of the Loess Platea,we propose to cultivate grassland in the area by planting Aa on the mountainous slopes and Alfalfa on the more or less level land with relatively more water supply.

Key words: Alfalfa, Astragalus adsurgens, Water use efficiency, Root biomass/shoot biomass ratio

摘要： 研究苜蓿和沙打旺苗期水分利用与根冠比例。结果表明,沙打旺叶片对土壤水分的瞬时利用效率均高于苜蓿。沙打旺地下部与地上部生物量比和根长/株高比在不同水分条件下亦高于苜蓿,尤其在低水分时。在高水分下苜蓿单位水分消耗所形成的生物量较多,随着土壤含水量的降低而大幅度减少。苜蓿具有较高的蒸腾速率和较快的根系生长速率,因而造成土壤水分的过快消耗。总之,高水分生长条件易于苜蓿生产效率的发挥,但沙打旺对土壤水分环境变化的稳定性较强。结合多年的研究成果和黄土丘陵区的实际情况,提出在不同立地条件下,沙打旺可以种植在该地区的坡地,而苜蓿则应在水分条件相对较好的川地种植。

关键词: 苜蓿, 沙打旺, 水分利用效率, 根冠比