Characteristics of soil weed seed bank of alfalfa fields among different fore crops

To study the effects of fore crops on the characteristics of soil weed seed bank of alfalfa fields at second growing years, three different fore crops, which were Zea Mays, Lespedeza hedysaroides and Astragalus adsurgens, were designed by the inducing germination method. The results showed that, when the fore crop was Z.mays, the mainly weed of alfalfa field were Portulaca oleracea and Amaranthus retroflexus; When the fore crop was L.hedysaroides, the mainly weed were P.olerecea, Chenopodium aristatum and A.retroflexus; When the fore crop was A.adsurgens, the mainly weed were C.aristatum and A.sretroflexus. Density of soil seed bank had significant difference between L.hedysaroides and the other two fore crops (P0.05); Weed seeds of the soil seed bank mainly concentrated in 0－5 cm soil layer and the distribution of deep level was very little.