As rightly pointed out by Dr.Suresh, Allelopathy is an environment friendly approach and usually root, stem+ leaves, straw of rice is being used in many of the experimental studies. However, implementation at field level is not there. Please find enclosed some of the research articles in these lines. 

This is a good question, but does rice really have allelopathic effects. Maybe the rice just outgrows and shades the weeds out. Its great success is in flooded patties where very few other plants can survive the reduced soil conditions. 

Allelopathy is an environment friendly approach for weed control but also a factor causing autotoxicity in crop production. A number of compounds, such as phenolic acids, fatty acids, phenylalkanoic acids, hydroxamic acids, terpenes, indoles, and the labdane-related diterpenoid momilactones, have been identified as potential rice allelochemicals 

For details see; http://www.tandfonline.com/doi/full/10.1080/17429145.2014.912358

As rightly pointed out by Dr.Suresh, Allelopathy is an environment friendly approach and usually root, stem+ leaves, straw of rice is being used in many of the experimental studies. However, implementation at field level is not there. Please find enclosed some of the research articles in these lines. 

i have not study allelopathic effects of rice against weed suppression

Answer

Dear Dr. Mahbub,

Many Research papers on this apect have been Published in Allelopathy Journal http//:www.allelopathyjournal.org/.

Prof. S.S. Narwal Chief Editor Allelpathy Journal # 101, Sector-14

Rohtak-124 001, Haryana, INDIA

Ph/Fax: +91 1262-274101 Mobile: +91 9315496321 http//:www.allelopathyjournal.org/

Dear Md Mostofa Mahbub

Please have a look at these useful RG links.

Article Rice allelopathy and the possibility for weed management

Article Potential allelopathic effects of rice plant aqueous extract...

Article ALLELOPATHIC INFLUENCE OF RICE EXTRACTS ON PHENOLOGY OF VARI...

Article Allelopathic effects of rice on seedling development in whea...

Good luck!