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Rice-weed Competitiveness as Influenced by Weed Controlling Methods and Rice Genotypes in Dry Seeded Rice Culture

S.B. Naseem
Rice Fanning Systems Division, Bangladesh Rice Research Institute, Gazipur-1701, Bangladesh.

J.K. Biswas
Rice Fanning Systems Division, Bangladesh Rice Research Institute, Gazipur-1701, Bangladesh.

Wais Kabir
Bangladesh Agricultural Research Council, Farmgate, Dhaka-1215, Bangladesh

K.T. Ingram
Georgia Agril. Expt. Station, Griffin, GA 30223-1797, USA

Mahibul Hasan
Rice Fanning Systems Division, Bangladesh Rice Research Institute, Gazipur-170 l, Bangladesh

Abstract/ Executive Summary:

The competition for limited soil moisture is often in favour of the weeds rather than rice in dry seeded culture. The diversified weeds need to be controlled by all possible means to achieve a satisfactory yield of dry seeded rice. We investigated the different mechanisms of weed suppression through differbnt weed controlling methods and rice genotypes. Four contrasting rice genotypes, Binato (Traditional, tall and low tillering), IR44349-SKN-522-3-1-3 (improved, short, high tillering), IR64 (improved, intermediate height, moderate tillering), BPI Ri-10 (improved, intermediate height, moderate to high tillering) and 4 weed controlling methods, Butachlor, Butachlor + One hand weeding at 25 days after emergence (DAE), One hand weeding at 25 DAE and two hand weeding one at 25 DAE and the other at 45 DAE were used in this study. Plant height was observed to be an effective plant trait against weed growth. Tall rice genotypes intercepted more light at upper canopy for having, long and droopy leaves that helped close the canopy earlier than the improved genotypes which allowed less light underneath the rice plant for weed growth. Tall weeds grew well with long slender rice genotypes having droopy leaves but with intermediate and erect leafed rice plants grass, sedge and broad leaf weeds equally dominated. Weed dry weight was greatest in the Butachlor treated plots and the least in 2 hand weeded plots for all genotypes. It was also ascertained that weed suppression ability of rice genotypes was negatively related to its yielding ability. To minimize yield loss through rice-weed competition more study is needed to develop a new plant architecture that would help reduce weed infestation and have increased productive ability.

Keywords: Rice-weed, Competitiveness, Infouenced, Rice genotypes

Location: Masalasa, Tarlac in the Philippines

Start Date: 00-05-1993

End Date: 00-10-1993

Program Area: Variety and Species

Commodity: Weed management, Rice

Objectives:

To determine the rice-weed competitiveness in DSR culture as influenced by weed controlling methods and rice genotypes.

Methodology:

The experiment was carried out at IRRI rainfed lowland consortium site at Masalasa, Tarlac in the Philippines from May to October 1993. A split plot design with four replications was used where four levels of main plots were weed control measures. They were: Butachlor, Butachlor+ One hand weeding at 25 days after emergence, one hand weeding at 25 DAE and two hand weeding (25 DAE and 45 DAE) Four rice genotypes with varying agronomic traits were assigned in the subplots. Butachlor was applied at @ 20 kg ai/ha and was broadcast over the treated plots. The land was ploughed by three rototilling followed by two harrowing by a tractor in order to get a well pulverized soil. Fertilization was done @ of 100-30-30 kg of N-P₂O₅-K₂O/ha. One third of N and full amount of P₂O₅ and K₂O was applied during final land preparation, the rest N was applied at equal splits at 35 and 60 DAE. Seeds were line sown in dry soil using carabao (Filipino buffalo) drown lithao (country plow). A row spacing of 25 cm and about 25-30 cm plants per linear meter was maintained. The crop was grown under rainfed condition. During heavy rainfall excess water was drained out from the field to avoid flooding. Plant height form each subplot was recorded from 20 DAE to maturity from 10 randomly selected plants, Data were taken from the same plants during every time measurement. Stratified leafarea index (LAI) of rice was determined at 20, 40, 60 and 80 DAE and at crop maturity. Each time plants from for a sample area of O.25 m² was collected. For dry weight estimation, samples were collected at 20, 40, 60, 80 DAE and at maturity. On each sampling dates, weeds were collected from two I-linear meter rows and plants from single I-meter keeping undisturbed the harvested area. At crop maturity, weed samples were separated into grasses, sedges and broad leaves. Rice plants and weeds were cut at ground level, oven dried for 72 hours at 70° C and weighed. Date of canopy closure was identified when rice plant leaves in a row met the leaves of the next row. Grain yield was measured from an area of 2.5 m X 2 m² at the middle of each plot. Daily maximum and minimum temperature, relative humidity, rainfall, pan evaporation and solar radiation were gathered from meteorological unit at the IRRI rainfed lowland consortium site at Victoria, Tarlac (Data not presented). Soil matric potential (SMP) was measured at 10,20,30,40 em depth. Data were taken 3 times a week from every sub plot.

Source of Information: Bangladesh Journal of Agriculture, Vol:24 (2), PP: 17-31, 1999, ISSN: 0253-5408

Article Link (Online Journal):

Funding Source:

Budget:

Total Budget (Tk.) :

Achievement/Findings:

Based on the above results and discussion, it became visible that the taller was the rice plant stature the better was its weed suppression ability. This probably could be attributed to increased light interception by rice plant's top canopy, long droopy leaves that helped close the canopy earlier that allowed little 'light underneath for weed growth. Lacking this trait, conventional improved genotypes were less competitive than the traditional one. However, the traditional genotype did nor respond adequately to different weed control measures but the improved genotypes did. The traditional genotypes were low in tillering ability which was closely related to yielding ability. Low tillering has been .emphasized as a desirable trait in the development of the super rice cultivars being researched at International Rice Research. But the conventional HYG's are still high in tiller number. in other words, . an antagonistic relationship seems to exist between weed competitiveness and yielding ability. Therefore, to minimize yield loss through rice-weed competitiveness more studies are needed to exploit new . plant architecture that would produce satisfactory yield under different cultural management practices.

Knowledge Management: Journal