Investigation and analysis of weed community succession in winter wheat field of Shandong Province.
Objective: In the past 10 years, the species, quantity and occurrence area of weeds in winter wheat field of Shandong Province have changed significantly. The objective of this study is to clarify the succession law and reason of weed community, and to provide a theoretical basis for making precise control strategy of weeds in wheat field. Method: A total of 300 investigation sites were investigated in the winter wheat field of Shandong Province, and three areas were selected for each investigation site. The weed community in winter wheat field of Shandong Province for each area was investigated three times from 2009 to 2019 using inverted W-pattern sampling method, and the distribution and change rule of weed community in seven regions of winter wheat field of Shandong Province were analyzed. Result: The characteristics of weed community changes in winter wheat field of Shandong Province were: (1) Descurainia sophia and Capsella bursa-pastoris had always been the dominant weeds in winter wheat field of Shandong Province, and the relative abundance of D. sophia always ranked first in the three surveys, which was 20.68%, 22.49% and 22.24%, respectively, and C. bursa-pastoris always ranked in the top three, with the relative abundance of 15.49%, 15.77% and 14.51%, respectively. (2) There were more and more species of dominant weeds, and the degree of weed damage was more and more serious. In the 2009-2010 annual survey, there were only two species D. sophia and C. bursa-pastoris with an relative abundance of ≥10.00%. In the last two surveys, there were three species (increased Bromus japonicus) and five species (increased B. japonicus, Aegilops squarrosa and Galium aparine). (3) The occurrence and harm degree of gramineous weeds increased gradually. In 2009-2010, B. japonicus and A. squarrosa were mainly distributed in northwest plain region, north coastal region and central mountain region, in 2013-2014, they spread to the southern mountain region and plain regions of middle Shandong, and in 2018-2019, they had spread all over the province. The relative abundance of B. japonicus was 7.66%, 16.39% and 17.94% in the three surveys, and that of A. squarrosa was 3.08%, 7.61% and 11.38%, respectively. Although the total dominance of Lolium multiflorum, Alopecurus myosuroides and Avena fatua was not high, but it increased gradually. (4) The distribution of broad-leaved weeds such as Veronica persica and G. aparine was increasing. The relative abundance of G. aparine in the three surveys was 8.29%, 8.94% and 10.00%, respectively, which increasing year by year, and the distribution area was gradually expanding. Now it was widely distributed in all regions of Shandong Province, especially in the southwest plain region, the southern mountain region and central mountain region, and also in the northwest plain region. The relative abundance of V. persica in the three surveys was 1.08%, 1.18% and 2.05%, respectively, V. persica mainly distributed in the southwest plain region and southern mountain region, and had also been distributed in other regions. (5) The largest change of weed community was occurred in hill regions of eastern Shandong, and the species diversity showed a rising trend. In 2009-2010, the Shannon Wiener index, which reflected species diversity, was only higher than the north coastal region, ranking sixth. In 2013-2014, it surpassed the northwest plain region and plain regions of middle Shandong, ranking fourth. In 2018-2019, it ranked second, only was lower than that of the southern mountain region. Conclusion: The change of farming system, the spread and invasion weeds and the continuous application of single herbicide in large area obviously promote the change of weed community in winter wheat field of Shandong Province. According to the results of weed change in winter wheat field of Shandong Province, the comprehensive weed control strategies of chemical herbicide and agronomic measures, precise control technology and alternative use of herbicides with different mechanisms should be promoted.