Abstract

Abstract:
The seed banks are the sole source of future weed populations of the weed species both annuals and perennials that reproduce only by seeds as well as enhance the survival of a species by buffering against harsh environmental conditions or highly effective control methods and allowing them to germinate over a period of many years. But farmers of Bangladesh have little knowledge about the weed seed bank. So the experiment was undertaken with a view to evaluating the weed seed distribution pattern in different soil depths in order to estimate the potential weed population in the crop field. The experiment was conducted at the net house of the Department of Agronomy, Bangladesh Agricultural University, Mymensingh during April to September 2014. Soil samples were collected from 12 plots in three different depths viz., 0-5, 5-10 and 10-15 cm of Durba Chara Village in Vangamari union under Mymensingh district. A total of 33 weed species belonging to 17 families were found of which 23 species were broadleaved, 6 grasses and 5 sedges. Thirty weed species from19 annuals and 11 perennials belonging to the 15 families, 23 weed species from15 annuals and 8 perennials belonging to 10 families andonly 19 weed species from13 annuals and 6 perennials belonging to 11 familieswere identified at 0-5, 5-10 and10-15 cm soil depth, respectively. The seven dominant weed species i.e., Fimbristylis miliacea L., Lindernia antipoda L., Lindernia hyssopifolia L., Cyperu sdifformis L., Eleusine indica L., Hedyotis corimbosa L. and Eclipta alba L. were found atdifferent soil depths. The result revealed that weed density decreased with increase of the soil depth. The higher number of weed species and density were observed in 0-5 cm depth of soil followed by 5-10 cm and 10-15 cm depth of soil, respectively. All weed types viz. grasses, sedges and broadleaves were found in abundance at 0-5 cm depth than 5-10 cm and 10-15 cm depth. Annual and perennial weeds were also higher in 0-5 cm depth and annual weeds were dominant over perennial weeds at each of the three soil depths. Out of the total number of weed seedlings emerged from three soil depths, about 65% of seedlings emerged within two months (April-May) of commencement of germination trial and rest 35% seedlings emerged within last 4 months (June-September). Based on Sorenson’s Index of Similarity, the diversity of occurring weed species between 5-10 cm and 10-15 cm depths was lower as Sorenson’s Index of Similarity was the highest (81%) as well as between 0-5 cm and 10-15 cm depths was higher as Sorenson’s Index of Similarity was the lowest (69%).

Key words: floristic diversity, seed bank, crop field, Sorenson’s Index of Similarity