Comparative Study Of Allelopathy Of Legume Forages

Legume forages are very important in animal production owing to their high quality with abundant protein for livestock and the ability of nitrogen fixation in grassland.The application of legume forages in agriculture production in China has been expanded for recent years.However,with the allelopathy research advancing,strong allelopathic potential in many legumes was found and much attention was paid.Further research of allelopathy in legumes has great significance in optimizing planting patterns of inter cropping and rotation of legume forages with cereal crops or cash crops,controlling weeds in biological methods,breeding new cultivars with stronger allelopathy for weeds control and developing new bioherbicide and biopesticide.In this study,the allelopathy of six legume forages viz.,alfalfa(Medicago sativa L.cv. Alfaking),hairy vetch(Vicia rillosa Roth.),yellow sweet clover(Melilotus officinalis Desr.), white clover(Trifolium repens L.cv.Haifa),red clover(Trifolium pretense L.) and alsike clover(Trifolium hybridum L.),which were cultivated and utilized broadly in livestock production,was studied.The allelopathic effects of the aqueous extract of the legume forages on germination and seedling growth of Italian ryegrass(Lolium multiflorum Lam.cv. Tetragold) were evaluated.Differences in allelopathic effect of the legumes among species, growing stages and organs were discussed.The physiological mechanism of allelopathic inhibition effect of these legumes on germination and seedling growth of Italian ryegrass was studied.Nine phenolic acid compounds namely p-hydroxybenzoic,chlorogenic,caffeic,ρ-coumaric,ferulic,protocatechuic,syringic,vanillic and cinnamonic acid in aqueous extract of the legumes in different organs and growth stages were quantified by high performance liquid chromatography(HPLC).The allelopathy potential of these phenolic acids was also determined via bioassay.Pot and field experiments were conducted to verify and compare the potential of allelopathic suppression to weeds of yellow sweet clover, alfalfa and hairy vetch.The results showed that the germination and seedling growth of Italian ryegrass were all inhibited by the treatments of aqueous extracts of the legume forages with significant reductions of germination rate,shoot length,shoot dry weight,root length or root dry weight compared to control(p＜0.05).There were significant differences in mechanism and magnitude of allelopathy among the legumes(p＜0.05).Germination rate,root length and shoot dry weight of Italian ryegrass were reduced most by the aqueous extract of yellow sweet clover and alfalfa.While root dry weight and shoot length of Italian ryegrass were reduced most by the aqueous extract of red clover and alsike clover.The allelopathic effect of the aqueous extract of white clover was the weakest of the six tested legumes.The differences in allelopathy between organs of the legumes were also marked.The aqueous extracts of above ground part always showed significantly greater allelopathic effects than under ground part on germination and seedling growth of Italian ryegrass(p＜0.05).In addition,the results also indicated that the allelopathic potential of the legumes varied with growing stages.All of the tested legumes at blooming stages showed significantly stronger allelopathic effects than at branching stages(p＜0.05).The HPLC detection results showed that the nine phenolic acid compounds were all detected in the aqueous extracts of the six legume forages.Most of these phenolic acids had allelopathic effects on germination or seedling growth of Italian ryegrass,especially syringic,vanillic,protocatechuic,caffeic andρ-coumaric acid,treatments of which significantly inhibited the germination and seedling growth of Italian ryegrass(p＜0.05). The phenolic acids in the aqueous extract of legumes had some interactions in the process of exerting allelopathy to Italian ryegrass.The concentration of each phenolic acid or the total concentration of the nine phenolic acids was significantly different in the aqueous extracts of different legumes(p＜0.05).Phenolic acids concentration in the aqueous extract of yellow sweet clover was the highest,alfalfa and red clover followed,and the lowest was white clover.The phenolic acids concentrations in the aqueous extract of above ground part of the legumes were always higher than those of underground part.In addition,the phenolic acids concentrations in the aqueous extracts of all the legumes at blooming stage were significantly higher than those at branching stage(p＜0.05).It was also found that the differences in allelopathy among legumes,organs and growth stages were interrelated greatly with the concentration of the phenolic acid compounds in the aqueous extracts,the greater the concentration,the stronger the allelopathic effect.Almost every physiological index of the germination and seedling growth of Italian ryegrass was greatly affected by the allelochemicals in the aqueous extracts of the legumes.It was found that the amylase activity and seed vigor of germinating seeds of Italian ryegrass in most aqueous extracts treatments were significantly lower than those of control(p＜0.05),which resulted in the marked inhibition of seed germination rate.The concentrations of soluble sugar and chlorophyll in the leaf of Italian ryegrass seedling in most aqueous extracts treatments were also lower than those of control,which indicated that the available energy in the endosperm of Italian ryegrass was reduced and the photosynthesis was weakened.It was also found that the activities of SOD and POD were all greatly influenced by the treatments of aqueous extracts of the legumes.This indicated that the balance of activate oxygen metabolism was broken.In addition,the concentration of MDA in Italian ryegrass seedling was markedly higher in most treatments than that in control,which indicated that membranes in Italian ryegrass seedling were damaged.The pot and field experiments results showed that application of hay powder of yellow sweet clover,alfalfa and hairy vetch all greatly inhibited emergence and growth of weeds. Compared to the control,the significant reductions of weed species and weeds biomass including number and dry weight per unit area in hay powder treatments of the legumes were found(p＜0.05).It was also found that suppressive magnitude of the legumes to different weeds was species dependent.Annual bluegrass(Poa annua L.) and veronica persica(Veronica persica Poir.) were suppressed more by the hay powder of yellow sweet clover than alfalfa and hairy vetch,but barnyardgrass(Echinochloa crusgalli[L.] Beauv.) was suppressed most by the hay powder of alfalfa.In addition,the effective suppression to weeds need enough high application rate(=0.9 t/ha) of hay power of the legumes.More attention should be paid to the selection of proper legume species or varieties and the proper application rate and time when the allelopathy of these legumes was utilized in weeds control.