| Weed infestation is one of the most important limiting factors in crop production. Weed seed bank is the potential weed communities and is the real source of future weed populations in arable fields. The knowledge of weed seed bank dynamics is benefit for the integrated weed control strategy. In this research, the dynamics of weed seed bank and weed populations in wheat-rice cropping systems under different weed control managements were monitored for long-term and the seed bank of Alopecurus japonicus, the dominant weed in wheat fields were analyzed quantificationally. The dynamics of Beckmannia syzigachne seed dispersal by irrigation water were studied. All these results were useful in developing the integrated weed management strategy. In addition, the biological characteristics and seed bank dynamic of weedy rice, which is the most troublesome weed in rice field were also studied.In order to the occurrence, the harmfulness and biological characteristics of weedy rice in Jiangsu Province along the Yangtze River, the 280 direct-seeded rice fields in 28 county-level cities of 8 prefecture-level cities were selected and investigated. The biology characteristics of weedy rice were observed at the selected 6 sites along the Yangtze River where weedy rice infested seriously by means of plot sampling. The result showed the proportion of weedy rice occurrence ranged from 78% to 100%, the average density was about 2-9 individuals/m2 and the overall value of weedy rice was more than 20%, which caused 8.2%-82.3% yield loss of rice. The investigation results outlined from the selected 6 sites demonstrated that weedy rice had some differences in amaranthine of leaf ring and auricle and the brown basilar stalk from cultivated rice. The weedy rice grew flourisher, produced more tillers than cultivated rice at seedling stage, and the tiller angle of weedy rice was 20°bigger than cultivated rice which made its plant-type looser.. Weedy rice, in general, was 8-10 cm taller than cultivated rice. Though the weedy rice produced larger quantity of seeds per plant than cultivated rice, the seed fertility was only from 78% to 86% which was lower than cultivated rice. The 1000-seed-weight was only about 18.93-20.10 g. Weedy rice was about one month earlier matured and early browning compared with cultivated rice. When maturation, most of weedy rice seeds shattered onto soil. The optimum time for manual removal of weedy rice is at the beginning of tillering and the flowering when it was easy to identify from cultivated rice.The seed shattering of weedy rice were the most important input of its seed bank, and the seed bank is the key of weedy rice persistence, so the knowledge of weedy rice seed bank dynamics is very useful to its integrated weed management (1WM). For this purpose, six sites of six cities along the Yangtze River in Jiangsu Province, China were chosen for the research. In these sites, three consecutive years’dynamics of weedy rice seed bank were studied and the relationship between the seed bank and population were analyzed. The seed bank density of weedy rice in all six sites displayed an increasing trend with seasonal fluctuation. The emergenced seeds were mainly concentrated at 0-10 cm soil layer and the seedling density was linear correlative with the seed bank density. The exponential correlation curve fitted the relationship between cultivated rice yield loss and adult weedy rice density. According to the data investigated during the weedy rice life cycle, a semi-empirical mathematic model was developed with well fit of the experimental data for the prediction of the seed bank dynamics. With integrated the semi-empirical model and the exponential curve, weedy rice seed bank dynamics, occurrence and rice yield loss can be predicted, which may be useful to estimate weedy rice infestation level so that a practical control can be adopted before rice planting.In addition, we conducted a field experiment to detect the germination characteristics, overwintering depletion of weedy rice seeds at different burial density and under different burial depth in order to provide us useful information in the control of weedy rice seed in seed bank. The results showed that the weedy rice seeds in shallow soil depleted faster than in the deep soil. The germination rates of weedy rice reduced significantly with time extended seeds when buried at the soil with different depth, but the seeds buried in deep soil kept higher germination ability that buried in shallow soil. There was no significant influence of burial density on seed germination. The logistic model can describe the relationship between the germination rate and time better under different burial densities or burial at different soil depth. The information was benefit for the control of weedy rice seeds in seed bank.The imput of seed bank was main influenced by the weed seed dispersal. In the middle and lower reaches of the Yangtze River valley, rice-wheat cropping system is the most prevailing. In the growing season of paddy rice, irrigation is regularly carried out and the irrigation water was the important agent for seed dispersal. So it is of great importance for us to undersatand the seed dispersal by irrigation water flow in this region. Therefore, several dispersal experiments of Beckmannia syzigachne, the most important weed in wheat field in this region were conducted during year 2009 and 2010 at Baihu Farm, Anhui province, China,. In order to track the seed shift, a dying seed technique was developed to dye seeds using safranine T. The dyed B. syzigachne seeds can be dispersed for a long distance by irrigation water along the irrigation ditch when released at the water entance of irrifation ditch. When they were released at the center of flooded field, the dyed B. syzigachne seeds can also be dispersed by the water and influenced by wind and the dispersal range extended with time. After ploughing and harrowing, the seed dispersal area spread more widely. We tried and succeed in developing a simple model that could fit the data obtained from the release experiment in irrigation ditch well. From the model, it was clearly that the seed dispersal pattern changed and the longer time the irrigation continued the more dispersive and farther the dyed seeds dispersed. In conclusion, our study indicated that the weed seeds can be mainly dispersed by irrigation water in both ditch and field when the irrigation carried out before rice planting and the wind blowing can contribute to the dispersal process. Water dispersal may be main pathway that influences the spatial deposition and distribution of weed seed bank in the paddy fields.A field experiment under rice-wheat cropping system was conducted to evaluate the effects of five different weed management strategies:manual weeding (MA), chemical weeding (CH), weed free (WF1), weed free without water interception (WFO) and a check with water interception (CK), which is lasted for 12 years. The dynamics of weed seed bank and weed populations were investigated and analyzed. The results showed that under different weed management strategies, species richness index and Shannon-Wiener index decreased and Simpson’s dominance index increased steadily when soil seed bank managed by the above five weed management strategies, but the Pielou evenness index of weed seed bank showed no significant changes. Except for CK, The density of weed seed bank declined annually, and the sequence for the effects of weed seed depletion was WF1>WFO>CH>MA>CK. The density of weed seed bank in the treatment of WF1 decreased about 92% in 12 years. It indicated that the interception of water can stop the seed bank imput from water dispersed seeds so that the depleting of seed bank would be faster. In addition, there were evident changes in relative abundance of weed species among the potential weed communities, and differences between community similarity index within management strategies increased with the year. The density and species composition of aboveground weed commuities also showed marked changes.Another field experiment was conducted during year 2006 to 2012, continuing the work of Li (2009), to evaluate the effects of five different weed management strategies:chemical weeding without water interception (CHO), chemical weeding with water interception (CHI), mechanical blowing weed seeds (MB), net gaining weed seeds (NG) and two times chemical weeding (CH2), on the dynamics of weed seed bank under rice-wheat cropping system. The results showed that under different weed management strategies, species richness index, Shannon-Wiener index and Pielou evenness index decreased and Simpson’s dominance index increased steadily when soil seed bank managed by the above five weed management strategies. Except for CHO, The density of weed seed bank declined annually, and the sequence for the effects of weed seed depletion was CH2>NG>MB>CH1>CH0. The density of weed seed bank in the treatment of CH2 and NG decreased about 57% and 59% in 7 years, respectively. There were evident changes in relative abundance of weed species among the weed seed banks, and differences between community similarity index within management strategies increased with the year. The density and species composition of aboveground weed communities also showed marked changes. The matrix model was used for the quantificational analysis of the seed bank dynamics of Alopecurusjaponicus, a dominant weed in wheat field, and the predicted data were close to the investigated data.The research indicated that the key to control the weed populations is depleting the seed bank. The knowledge of the weed seed bank dynamics is benefit for us to developing the weed control measures. Moreover, the dynamics of weed seed bank can be simulated and predicted by models, which made the occurrence of weeds predictable. The seed rain is the most important imput way for the complement of weed seed bank, so it is important to reduce to seed rain in order to reduce the imput of seed bank. The irrigation water played an important role in weed seed dispersal and the water dispersed seeds could be a part of seed bank imput. The field study showed that the ecological weed control measures, such as net fishing weed seeds and mechanical blowing weed seeds were effective in decreasing the weed seed rain and it would be feasible ways to reduce the scale of seed bank, especially the seeds which have the high buoyancy, if integrated with water interception, so that use of chemical weed herbicides can be reduced. |
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