Abstract: Alfalfa(Medicago sativa L.) is recognized as a high yield and good quality forage and playing a key role in both forage supply and food security.The autotoxicity has been reported as one of the most important factors causing low yield of succeeding alfalfa crop.A germination bioassay was conducted to determine the toxic effect of soil aqueous extracts from different aged alfalfa standings in Qingyang and Dingxi,Gansu Province on seed germination rate of alfalfa,radish(Raphanus sativus L.),and wheat(Triticum aestivum L.) using paper germination test.The results indicate that an inhibition effect of soil aqueous extracts from different aged alfalfa standings in Qingyang on alfalfa seed germination was detected,the toxicity form high to low was as 5-year > 3-year > 9-year,and the relative germination rate of alfalfa treated by soil aqueous extracts from 5-y alfalfa standing declined 18% in comparison with that in control,meanwhile the reduction of relative plumule length and radicle length reached 69% and 80%,respectively.Alfalfa age below 4 years at Dingxi did not show significant autotoxicity effect due to low aboveground biomass accumulation under condition of annual average rainfall 391mm.Fallow and ploughing in fall was an effective method to breakdown the soil toxicity of above 5-year old alfalfa standing on three species′ seed germination.In alfalfa-wheat rotational system,alfalfa retained weak toxicity effect on the following wheat establishment.

Key words: Alfalfa, Soil aqueous extract, Autotoxicity, Seed germination

摘要： 采用自甘肃庆阳和定西地区不同年龄紫花苜蓿(Medicago sativa L.)土壤制备浸提液,应用纸上发芽法检测其对苜蓿、萝卜(Raphanus sativus L.)和小麦(Triticum aestivum L.)种子萌发的影响.结果表明:不同生长年龄苜蓿土壤浸提液对苜蓿种子萌发以及胚根和胚芽的抑制程度为年>3年>9年,在庆阳龄苜蓿土壤浸提液(00 g干土/L)中苜蓿发芽率下降18%,其胚芽和胚根显著受抑(P<0.0),比对照分别降低69%和80%.在平均降水391mm的定西,4年以下苜蓿土壤无明显自毒性;苜蓿秋季翻耕休闲有利于3个供试种的萌发及胚根和胚芽的生长,有效解除了年龄以上苜蓿土壤的自毒效应,苜蓿-小麦轮作系统中,苜蓿后茬小麦建植不受苜蓿毒性的影响.

关键词: 紫花苜蓿, 土壤浸提液, 自毒作用, 种子萌发