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Critical Crop-weed Competition Period in Wet Season Transplanted Rice

J. C. Biswas
Bangladesh Rice Rice Research Institute, Gazipur-1701

SK. A. Sattar
Bangladesh Rice Rice Research Institute, Gazipur-1701

S. B. Siddique
Bangladesh Rice Rice Research Institute, Gazipur-1701

Abstract/ Executive Summary:

Rice-weed competition, dominant weed species and their impact on the yield of transplant Aman 'rice were studied in two field experiments. The critical rice-weed competition period varied from 30 to 40 days depending on weed species and their abundance. The total number of weeds removed and their dry weight increased gradually and increase in the frequency of weeding. The highest number of weed removed was 169/m² weighing 52 g/m² only. Sedges were the major weed group and Cyperus difformis was the dominant species followed by Cynodon dactylon and' Monocnorla' veginalis, respectively, in 1987. Grass was the major weed group in 1988 and the dominant species was Cynodon dactylon. The other major weeds were Fimbristylis littoralis and Cyperus difformis.

Keywords: Critical crop-weed competition, Wet season, T. Aman, Rice

Location: Bangladesh Rice Research Institute (BRRI) experimental farm, Joydebpur

Start Date: 00-00-1987

End Date: 00-00-1988

Program Area: Crop-Soil-Water Management

Commodity: Infestation

Objectives:

To determine the critical period of rice-weed competition, dominant weed species and their effect on rice yield.

Methodology:

Two field experiments were conducted in 1987 and 1988 at the Bangladesh Rice Research Institute (BRRI) experimental farm, Joydebpur to identify the critical rice-weed competition period in the wet season second rice crop. The soil of the experimental sites were clay loam with pH ranging from 6.8-7.5, and a total N content of 0.06- 0.07%. The treatments were, weeding at 0, 10, 20, 30, 40, 50 and 60 days after transplanting (DT). In 1988, one additional treatment, season-long weed-free, was included. The unit plot size was 3x3 m. The experimental plots were laid out in a randomized complete block design with three replications. Fertilizers were applied at the rate of 80, 60, 40, 25 kg N. P₂0₅, K₂0, and S per ha as urea, triple super phosphate, muriate of potash and ammonium sulfate, respectively in 1987. The amount of N from ammonium sulfate and urea were adjusted. In 1988, the applied fertilizer doses were 60, 40, 40 and 20 kg of N. P₂0₅, K₂0 and S per ha from the same sources except in case of S which was applied as gypsum. All P, K and S were applied as basal doses. Urea was applied in three equal splits : 15 DT, at the maximum tillering stage (MT) and at the panicle initiation stage. The crop was grown as an irrigated crop and no water stress occurred at any time during the growing season. Carbofuran (2, 3 Dihydro-2, 2 dimethyl 7-benzofuran methyl carbamate) as Furadan 3G at the rate of 10 kg/ha was applied at MT to control insects. Weeds were collected from the treatment plots, identified, grouped into grass, sedge and broadleaf classes, counted and their oven dry weights were recorded separately for the different treatments. Grain weights of rice form the whole plots were taken. and adjusted at 14% moisture content; plant height and panicle numbers at maturity were recorded. The data were analysed following standard statistical procedures

Source of Information: Bangladesh Rice J. 1 (1): 17-22 (1990)

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

There was a 2-29% yield reduction considering the critical competition period upto 40 day and the highest yield of 4.20 t/ha was obtained from the weed-free plot in 1988, when grasses were the dominant weeds. Similarly, considering the critical competition period upto 30 d, there was a 8-16% yield reduction in 1987 caused mainly by sedges. De Datta (1979) reported a yield reduction of 67% due to the combined effect of grass, sedge and broadleaf weeds, the dry weight of which totaled 330 g/m². The much lower magnitude of rice yield reduction observed in our experiments was due to a much lower weed dry weight (52 g/m²) and to, obviously, a much less intense rice-weed competition.

Knowledge Management: Journal