Abstract
This study was conducted at the research fields of Agronomy Field Laboratory and in the net house of Department of Agronomy, Bangladesh Agricultural University, Mymensingh. The objective of this study was to compare the in situ and ex situ floristic diversity of soil weed seedbank in boro rice. The soil weed seedbank status was observed through weed survey at research fields and seed germination method in the net house. Five fields were selected randomly with four replications. Soil samples were collected to a depth up to 15 cm and placed in plastic pots in the net house. Weed seedlings that emerged were identified, counted and removed at 30 day intervals throughout the four months emergence period. At the same time, weed survey was done using a 0.25 m–2 quadrate. Diversity was computed by the Shannon index (H’). Under in situ condition, 31 weed species belonging to 15 families germinated and 33 weed species belonging to 17 families germinated under ex situ condition. The family Cyperaceae had the highest species richness under both in situ and ex situ conditions. The five most dominant weed species under in situ condition based on importance value were Eleocharis atroperpurea > Cyperus difformis > Echinochloa crusgalli > Monochoria vaginalis > Lindernia antipoda whereas, under ex situ condition, two new weed species, Fimbristylis miliacea and Echinochloa colonum were observed in the dominant list instead of Monochoria vaginalis and Lindernia antipoda having slightly different rank and order. The ex situ density was 2721 plants m–2, approximately four times higher than the 700 plants m–2 observed under in situ situation and similarly ex situ condition had higher Shannon Index (H’) value (H’=2.412) indicating greater diversity than in situ (H’=2.211) condition. The information obtained from the study would help determine the infestation potential of identified species, which could lead to improved management strategies.
 J. Bangladesh Agril. Univ. 16(3): 396–402, December 2018
Highlights
Rice is the world’s single most important crop and a primary food source for half of the world’s population
Composition of weed species under in situ condition Agronomy Field Laboratory, where in situ evaluation has been done, were occupied with 31 weed species belonging to 15 families and 24 genera representing diversity in their composition (Table 1)
Eight weed species were found from Poaceae family, five weed species from Cyperaceae family, three from Amaranthaceae family, two weed species from each of the family Commelinaceae, Pontederiaceae and Polygonaceae and one weed species from each of the family from Araceae, Azollaceae, Compositae, Hydrophyllaceae, Marsileaceae, Nymphaeceae, Onagraceae, Rubiaceae and Scrophulariaceae
Summary
Rice is the world’s single most important crop and a primary food source for half of the world’s population. Chauhan and Johnson (2011) reported as high as 95% yield reduction in rice due to weed competition throughout the rice growing season. This loss is, a serious threat for the food deficit countries like Bangladesh. One of the most important, yet often neglected, weed management strategies is to reduce the number of weed seeds present in the field, and thereby limit potential weed populations during crop production. This could be accomplished by managing the weed seedbank
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