Study On Weed Community Complex And It's Control With Herbicide Mixture In Jiangsu Province

Weed community complexes of summer, autumn crop and paddy fields in Jiangsu Province were studied. Soil weed seed banks (potential weed communities) were sampled in representative continuous dry-cropping and rice-wheat rotation fields. Elutriation of sampled soil and account of weed seeds were used to study characteristics of the potential weed communities in these two kinds of farmlands, and canonical correspondence analysis (CCA) was applied to study the flora of potential weed communities associated with environmental conditions. Keeping wet, the weed seeds in soil banks were germinated in greenhouse to analyze the characteristics of potential weed communities of two different cropping systems; and also keeping submerged to compare the two methods' weed germination quantities of two kinds of cropping systems, to discuss the mechanism of weed control effect of rice-dry rotation systems. Germination and elutriation were used to study potential weed communities of continuous dry-cropping fields to compare the difference between the two methods. Real weed communities were surveyed to explain the comprehensive structure characteristics of real and potential weed community complexes integrated with the results of the potential weed community structure. Isoproturon plus DiCaoQiang and isoproturon plus metolachlor two mixture had good control effect on potential and real weed communities. The detailed results are as following: 1. The structure characteristics of potential weed communities in Jiangsu ProvinceWeed seed banks of 12 samples of continuous dry-cropping and 19 samples of rice-wheat rotation fields were studied through using elutriation. Normally, all weed seed banks include three types of weeds in two different cropping systems; and if weeds in included paddy weeds, there were more hydrophilous weeds in summer maturity crop fields, such as equal alopecurus (Alopecurus aequalis Sobol.), contrarily, more xerophilous weeds. Through counting sampled soil seedbank, 48 weeds were recorded. Among them, 43 weeds were found in seed bank of rice-wheat rotation fields, 36 in continuous dry-cropping fields, of which gramineae (Poaceae) is the most, the second sedge family (Cyperaceae).Difformed galinagle (Cyperus difformis L) and Japanese Mazus {Mazus japonicus (Thunb.) O. Kuntze) had the highest frequency and the largest amount of seed bank density in fields of two kinds of cropping systems. There were the marked differences of seed bank density in different fields, and seed density of rice-wheat rotation fields were much higher than that of continuous dry-cropping fields. 60%-90% seeds were found in 0-10 cm soil layer in fields of two kinds of cropping systems with distributing decreasingly in the lower soil layers. Seed bank structure was relatively stable in the fields with stable cultivation and cropping systems; and the vertical distribution of seeds in the fields under deep-ploughed was relatively even. The results of canonical correspondence analysis showed that cropping systems was the main factor influencing seed bank structure, and the second was soil pH. The artificial management level had very great influence too.2. The influence of cropping system and water condition to potential weed communitiesUsing induced emergence under keeping wet in greenhouse, potential weed communities of continuous dry cropping and rice-wheat rotation fields were investigated. Results indicated that compositions of the seed bank were similar to the results of elutriation, but the size of each weed species was different in which most of the weed seeds belonged to summer crop fields. The results under different water conditions in germination indicated that rice field-upland field rotation could control weeds effectively after a long time of the same cropping systems, otherwise the essential precautionary measures should be taken.3. Comparison of characteristics of potential weed communities in continuous dry-cropping systems with elutriation and induced emergenceUtilizing emergence inducement and elutriation to study weed seed banks o...