Study On The Floating Characteristics Of Weeds And Its Application In Ecological Weed Control In Rice-Wheat(Rape) Cropping Area

Rice-wheat(rape)continuous cropping is the most important planting model in the middle-lower Yangtze area in China.The diversity of weeds in this planting model is high,the structure of weeds is complex,and the crops are seriously damaged.In recent years,due to the excessive application of chemical herbicides,many problems such as environmental pollution,pesticide residues,herbicide resistance,and farmland biodiversity reduction have emerged.China puts forward the main development direction of agriculture in the future:to ensure zero growth of pesticide use and return the motherland to green water and green mountains.To achieve this strategic goal,ecological and sustainable weed management measures should be developed to replace traditional chemical weeding.In order to achieve the sustainable management of weeds,the morphological indicators of common weed fruits and seeds in the continuous cropping area of rice and wheat(rapeseed)in the middle-lower Yangtze area,as well as the microstructure adapted to the spread of irrigation water flow were examined.The mechanism of weed seed adaptation to water flow was also clarified.From an ecological point of view,how to cut off the propagation of weeds and carry out comprehensive weed control measures were studied aiming at depleting the soil weed seed bank,which provides an important theoretical basis for the sustainable management of weeds.The specific research results are as follows:1 The physical form and floating ability of common weed seeds in rice-wheat(rapeseed)continuous cropping areaA total of morphological basic indexes of 110 weeds species from 35 families in rice and wheat(rapeseed)were measured,and the floating time in actual paddy fields was counted.The results showed that the morphological indexes of weed seeds were significant different.Among them,the relative volume was mainly concentrated in 1.00-10.00 mm3.The hundred-seed weight of weed seeds was mainly concentrated in 9.00-100.00 mg.The shape of the weed seeds was diverse,including ellipse,flat,triangular and quadrangular,etc.Among which the elliptical weed seeds had the largest number with 16 species,accounting for 14.55%.Weeds are mainly spread by seed dispersal and fruit dispersal.The weeds dispersal through fruits were most the achenes.Some weed seed actually contains accessory structures such as awn,crown hair,wings and perianth.According to the weed seed floating test,90.91%of the weed seeds could float for more than 12h in the irrigation water of farmland,there were 47 weeds species with a floating time of 48-120 h.Weed seeds from Gramineae,Compositae,Polygonaceae,Umbelliferae and Ranunculaceae had a strong floating ability with a continuous floating time of over 400 h,while those from Pontederiaceae,Malvaceae,Labiatae,Caryophyllaceae,Convolvulaceae,and Commelinaceae had weak floating ability.The weed seeds in continuous cropping area of rice and wheat(rape)are mostly floating and can dispersal with irrigation water.lt provides an important basis for preventing weeds.2 Microstructure of common weed seeds in rice-wheat(rapeseed)continuous cropping area adapted to floatingWeed seeds in rice-wheat(rape)continuous cropping area dispersal via flowing water during irrigation of the rice crop.However,the ability of these weed seeds to utilize water dispersal and their structural mechanisms remain unclear.To clarify the micro structural basis of the ability of weeds to spread by water,seeds from 110 species of weeds from 35 families were selected for this study.Using frozen sectioning technology,weed seed slices were made to observe and the proportions of parenchyma,stomata,and lignified tissues were assessed,and morphological indicators,such as relative size,appendages,100-seed weight,and seed type,were used for integrated analysis.Multivariate statistical analysis showed that the floating time of weed seeds was significantly positively correlated with the shape,cavity and parenchyma of the weed seed and negatively correlated with lignification.Cluster analysis divided all the tested seeds into four categories.The first category was super strong floating weeds,which had a large area of parenchyma tissues or air cavity structures and floated on water surfaces for more than 400 hours;the second category was strong floating weeds,which had a flat shape,containing parenchyma or air cavity structures with a floating time of 120-400 h;the third category was floating weeds,which were usually dense in structure with a floating time of<120 h;the fourth category showed no floating ability,seeds of which with a large size and mass,and dense structures.Most of the main weeds of farmland had strong floating ability,and the floating ability of weeds was closely related to the adaptability of their anatomical structures.This study provides a theoretical basis for understanding ecological adaptation and sustainable ecological control of weeds.3 The grass control effect of the integrated weed control technology in rice-wheat(rapeseed)continuous cropping fieldEcological weeds control measure is a ecological measure to cut off the dispersal of weeds and deplete the weed prevention and control measure in the field soils seed bank.In order to explore the effect of weeds control and its scope of application,continuous integrated grass control in Kunshan in southern Jiangsu,Huaian in northern Jiangsu and Suqian have been conducted since June 2016.Survey showed that 10137.99 ind/m2,8378.89 ind/m2 and 6703.26 ind/m2of the seeds could be averagely removed in Kunshan,Huaian and Suqian sites through net fishing operations.The soil weed seed bank density in the three places rice season decreased by 42.28%,32.05%,47.37%,wheat(rape)season decreased by 47.51%,48.08%,47.56%.The decrease rate of wheat weeds,grass weeds and sedge weeds was slightly faster than that of rice weeds and broadleaf weeds.The seed bank succeeded in the direction of decreasing number,increasing diversity,and stable community structure.The total occurrence of weeds on the ground in the three places decreased by 52.39%,44.14%and 42.21%at the seedling stage in the rice season respectively,and decreased by 44.30%,51.52%and 36.35%at the mature stage respectively;which decreased by 65.61%,64.82%and 63.96%at the seedling stage,and decreased by 49.59%,43.00%and 66.17%at the mature stage in wheat(rape)season.The occurrence of major weeds in the field had decreased significantly.After four years of ecological weeds control measure,the number of chemical herbicides used in Huaian and Kunshan has been reduced by 2-4 times.Compared with traditional chemical weed control,ecological weeds control measure can also increase crop yield.It is a green,efficient and sustainable ecological weed control measure.