Weed seed distribution at different depths of soil in a crop field

Abstract

The seed banks are the sole source of future weed populations and enhance the survival of a species by buffering against harsh environmental condi- tions or drastic weed control measures. Seed bank allows weed species to germinate over a period of many years. This experiment was undertaken with a view to evaluating the weed seed distribution pattern at 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 during April to September 2014. Soil samples were collected from 12 plots at three depths viz. 0-5, 5-10 and 10-15 cm of Durba Chara village of 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 from 19 annuals and 11 perennials belonging to the 15 families, 23 weed species from 15 annuals and 8 perennials belonging to 10 families andonly 19 weed species from 13 annuals and 6 perennials belonging to 11 families were identified at 0-5, 5-10 and 10-15 cm soil depth, respectively. The seven dominant weed species i.e. Fimbristylis miliacea L., Lindernia antipoda L., Lindernia hyssopifolia L., Cyperus difformis L., Eleusine indica L., Hedyotis corimbosa L. and Eclipta alba L. were found at different 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 at 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 at 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 first 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%).