Preliminary Study On Autotoxicity Effects Of Alfalfa On The Loess Plateau

Alfalfa(Medicago sativa L.)is an important forage for developing grassland animal husbandry,improving agricultural system stability and increasing the income of the farmers.The autotoxicity effects of alfalfa affected the re-establishment of pasture which relates to the persistence and the stability of grass production.With the expansion of China's alfalfa acreage,the related research on autotoxicity of alfalfa holds certain importance.In order to study the existence of autotoxicity of alfalfa on Loess Plateau in Gansu and the autotoxicity effects of the germination of seeds,alfalfa rhizospheric soils and plants from different stands were collected form Qiangyang and Dingxi on the Loess Plateau,Gansu.The aqueous extracts from,soils and plants on seed germination were investigated by filter paper method.1)The aqueous extracts from 5-year alfalfa soil from Qingyang had no siginificant inhibition to alfalfa seed germination,but the shoot length and radicle length significantly lower than the control's 67%and 75%respectively.The aqueous extracts made the shoot and radicle Short and thick,significantly inhibited.At the same concentration,the germination rate,the shoot and the radicle length of wheat and radish,when compared with the control without a significant reduction,showed obvious effects of autotoxicity.It was found that water-soluble materials of autotoxicity by inhibiting the growth of shoot and radicle to influence the plant health.The results showed aqueous extracts from alfalfa soil in low concentration(50gDM/ml)treatment promoted the growth of alfalfa seedlings.2)There was found to be a relationship between the autotoxMty of alfalfa from Qingyang and alfalfa age.In the Qingyang region,the inhibition of the aqueous extracts from alfalfa soil could be arranged as:5-year alfalfa soil,3-year alfalfa soil and 9-year alfalfa soil.The results could be used to guide alfalfa re-establishment and wheat-alfalfa rotation,on the Loess Plateau.3)The germination,shoot length and radicle length from soil extracts under after tillage fallowing one month were higher than that samples from before tillage.This showed that tillage can dilute the level of autotoxicity,effectively reducing the autotoxicity. 4).When the concentration of aqueous extracts from alfalfa plants is greater than 20g DM/ L,It was found that the indicators at plant growth were significantly inhibited.In high concentrations,aqueous extracts caused shoot and radicle degeneration,or even the death of alfalfa seed.The aqueous extracts from different alfalfa plant parts had inhibitive effects on germination and seedling growth.Alfalfa plants contain water-soluble material of autotoxicity.Extracts from alfalfa flowers had the strongest inhibition effect on seed germination and seedling growth,followed by extracts from alfalfa leaves.For better management it is proposed that harvesting before the flowering period,to reduce the accumulation of flower litter,thereby reducing the effect of alfalfa to new seedlings.Shoot and radicle elongation of alfalfa were inhibited more than germination was by alfalfa extracted solution.Aqueous extracts from Qingyang 4-6 year stands had the most inhibitory effects to shoot length compared with the aqueous extract from Qingyang 10 year stand.For 4-6 year stand alfalfa;rotation should be adopted to overcome the autotoxicity effects.5)The effects of the aqueous from soil and plant,on germination,shoot length and radicle length showed the same trend.This indicated the materials of autotoxicity exist the sink -source relations.The autotoxicity of the aqueos extrats from the alfalfa plants performed more strongly than those from the alfalfa soil.The materials released from alfalfa plants and the accumulation of rotting toxic substances were buffered in the soil.