Diversity Of Soil Weed Seedbank In Response To Different Tillage And Cropping Systems In Shanghai Pudong

Rice is one of the main food crops in Shanghai.Farmland productivity declines and loss of biodiversity were caused by excessive use of chemical fertilizers and pesticides and successive cropping.Therefore,rice-broadbean rotation,rice-fallow rotation and mouldboard ploughing were promoted in Shanghai instead of rice-wheat rotation these years.The above-mentioned tillage and cropping systems provide opportunities for maintaining the diversity of weeds in paddy fields while ensuring crop yields and improving land quality.The soil seedbank is a potential weed population and an important mechanism for the maintenance of weed biodiversity.Testing the effects of different tillage and cropping systems on weed species density and diversity within the soil seedbank contributes to maintain the ecological balance of farmland on the basis of high rice yield.It is beneficial to the scientific management of weeds and the sustainable development of agriculture and environment.Field studies were carried out to evaluate the effects of different tillage depths(chisel ploughing and mouldboard ploughing)and cropping systems(rice-broadbean rotation,rice-fallow rotation and rice-wheat rotation)on the characteristics of soil weed seedbank.Water washing-microscopic examination,germination experiment and community survey was done in2016 and 2017.The difference among different systems in species combination,dynamic changes,density,vertical distribution,diversity of soil seedbank and rice yields were analyzed.Below are the key findings of this research:1)The species composition of soil seedbank of Shanghai Pudong was dominated by Gramineae and Cyperaceae,with annual(84%),tussock and erect form(56%),and native(64%)weed species as the main species.The common dominant species were Beckmannia syzigachne,Eleusine indica,Eclipta prostrata and Veronica undulata in2016,and turned into Sclerochloa dura,Cardamine hirsute and Capsella bursa-pastoris in 2017.Leptochloa chinensis and Veronica peregrine are dominant species in autumn.2)There were significant differences in density of weed soil seedbank in response to different tillage depths and cropping systems.The density in MT-RB(8.17*10~4ind./m~2),which mainly concentrated in upper layers in soil,was much higher than that in MT-RW(5.33*10~4ind./m~2).There is no significant difference between MT-RB and MT-RF.More seeds in MT than in CT were found except MT-RW,and distributed evenly in CT while mostly in 0-10cm in MT.3)There were significant differences in diversity of weed soil seedbank in response to different tillage depths and cropping systems.Species richness and Shannon-Wiener index were highest in CT-RW,were 12.75 and 2.10 respectively,which were approximate in CT-RF and MT-RF.But they were 6.75 and 1.57respectively,lowest in MT-RW.Species richness,Shannon-Wiener index,Simpson index and Pielou index were higher in upper layers in all CT systems,which were contrary to Shannon-Wiener index,Simpson index and Pielou index in MT systems.Only Simpson index and Pielou index had significant differences in different depths in MT systems.4)Transient soil seedbank was obtained from germination experiment.There were no significant differences in diversity of weed soil seedbank in response to different tillage depths and cropping systems.Except that,the density in under layers is higher in CT-RW than in CT-RF and MT-RF,the Shannon-Wiener index and Simpson index in upper layers is higher in CT-RF than in MT-RF.Therefore,tillage depths and cropping systems affect persistent soil seedbank more,and tillage methods have the maximum influence.5)There were significant differences in rice yields in response to different tillage depths and cropping systems.The highest yield of rice was 10077.76kg/hm~2 in CT-RB,similar to that in CT-RF and MT-RF,much higher than the average yield-8035.10kg/hm~2 in Shanghai.And the yield was lowest in MT-RW and MT-RB,which was only 5717.25 kg/hm~2,The weed soil seedbank in Shanghai Pudong rice fields is dominated by annuals,tussock and erect form and native species.Different tillage depths and cropping systems have larger influences on persistent soil seedbank than transient soil seedbank.To improve cultivated land quality,increase rice yields and agricultural productivity,CT-RF and MT-RF are advocated to protect weed density and diversity,which is considered to be an adaption to unpredictable environment.