brown rice varieties compared to white rice except in the inhibition of seed germination (Table 4) and these results indicate that brown rice varieties have higher allelopathic potential than white rice varieties. There is a belief that varieties with coloured pericarps have higher nutraceutucal properties than white rice. Some experimental evidences also show that brown rice contains more nutrients and antioxidents than white rice (Wathugala, 2014). Jung et al. (2004) showed that rice residues of varieties with coloured hull have higher allelopathic potential on barnyard grass compared to varieties with colourless hull.
Four rice varieties showed stimulatory effects on shoot length and inhibitory effects on all other measured parameters, and one variety (At306) showed stimulatory effects on dry weight (Table 1). Rice (1984) reported that stimulatory effects may happen at low concentrations of allelopathic substances but inhibitory effects at higher concentrations. Therefore these varieties may have released very low amounts of allelochemicals during decomposition and the residues may decompose quickly and release plant nutrients to enhance barnyard grass growth. Out of the 40 varieties tested in this experiment all varieties except two (Bg304 and At306) showed more than 20 % average inhibition on barnyard grass growth, indicating the importance of residue incorporation to paddy soil. In this experiment 1 % of rice residue was incorporated to prepare the soil mixture. Therefore, 4714 kg ha-1 of rice residue (3 × 7 × 4 × 108 / 22 × 81 × 103 kg ha-1 for 10 cm deep of soil) would be theoretically required for allelopathy to occur in the field. However many factors other than the amount of residue may also be involved in allelopathic activity such as soil conditions, climatic conditions and management conditions. Also, allelochemicals released from decomposing straw may not remain active for long under field conditions due to further microbial activity. Therefore, different results would be expected in field conditions. However, according to the results obtained in this study, the more rice residues remaining in the paddy soil, the greater the concentration of allelopathic substances released during decomposition and higher degree of weed control. Some Sri Lankan farmers leave all the residues (straw) in the field but some farmers still burn rice residues (straw) before field preparation for the next season. Weeds can be better controlled by incorporating plant residues that release a greater fraction of allelochemicals in the soil (Elijarrat & Barcelo, 2001). Therefore, improving the allelopathic properties of commonly cultivated rice varieties can be used as an eco-friendly approach to combat paddy weed problem by reducing herbicide usage.
In Sri Lanka, the farmers mainly cultivate improved rice varieties but information on allelopathic potential of these rice varieties are lacking. This study provides information to develop rice varieties with higher allelopathic activity and also suggests that the allelopathic compounds released when rice residues (straw) decompose can act as a natural herbicide to control weeds. Therefore, incorporating rice residues (straw) to paddy soil can be used to reduce the cost of weed control in direct seeded rice ecosystems. However, further studies need to be conducted to evaluate the suppressive effect of rice residues applied under natural conditions.
ข้าวกล้องพันธุ์เปรียบเทียบกับข้าวขาวยกเว้นในการยับยั้งการงอกของเมล็ดพืช (ตาราง 4) และผลลัพธ์เหล่านี้บ่งชี้ว่า สายพันธุ์ข้าวมีศักยภาพ allelopathic สูงกว่าข้าวขาวพันธุ์ มีความเชื่อที่ว่า สายพันธุ์ มีสี pericarps มีคุณสมบัติ nutraceutucal สูงกว่าข้าวขาว บางหลักฐานทดลองแสดงว่า ข้าวกล้องประกอบด้วยสารอาหารมากขึ้นและ antioxidents มากกว่าข้าวขาว (Wathugala, 2014) จุงและ al. (2004) แสดงให้เห็นว่า ตกข้าวพันธุ์กับฮัลล์สีมีศักยภาพสูง allelopathic บนหญ้าลานยุ้งข้าวเปรียบเทียบกับพันธุ์กับฮัลล์สีใส Four rice varieties showed stimulatory effects on shoot length and inhibitory effects on all other measured parameters, and one variety (At306) showed stimulatory effects on dry weight (Table 1). Rice (1984) reported that stimulatory effects may happen at low concentrations of allelopathic substances but inhibitory effects at higher concentrations. Therefore these varieties may have released very low amounts of allelochemicals during decomposition and the residues may decompose quickly and release plant nutrients to enhance barnyard grass growth. Out of the 40 varieties tested in this experiment all varieties except two (Bg304 and At306) showed more than 20 % average inhibition on barnyard grass growth, indicating the importance of residue incorporation to paddy soil. In this experiment 1 % of rice residue was incorporated to prepare the soil mixture. Therefore, 4714 kg ha-1 of rice residue (3 × 7 × 4 × 108 / 22 × 81 × 103 kg ha-1 for 10 cm deep of soil) would be theoretically required for allelopathy to occur in the field. However many factors other than the amount of residue may also be involved in allelopathic activity such as soil conditions, climatic conditions and management conditions. Also, allelochemicals released from decomposing straw may not remain active for long under field conditions due to further microbial activity. Therefore, different results would be expected in field conditions. However, according to the results obtained in this study, the more rice residues remaining in the paddy soil, the greater the concentration of allelopathic substances released during decomposition and higher degree of weed control. Some Sri Lankan farmers leave all the residues (straw) in the field but some farmers still burn rice residues (straw) before field preparation for the next season. Weeds can be better controlled by incorporating plant residues that release a greater fraction of allelochemicals in the soil (Elijarrat & Barcelo, 2001). Therefore, improving the allelopathic properties of commonly cultivated rice varieties can be used as an eco-friendly approach to combat paddy weed problem by reducing herbicide usage. In Sri Lanka, the farmers mainly cultivate improved rice varieties but information on allelopathic potential of these rice varieties are lacking. This study provides information to develop rice varieties with higher allelopathic activity and also suggests that the allelopathic compounds released when rice residues (straw) decompose can act as a natural herbicide to control weeds. Therefore, incorporating rice residues (straw) to paddy soil can be used to reduce the cost of weed control in direct seeded rice ecosystems. However, further studies need to be conducted to evaluate the suppressive effect of rice residues applied under natural conditions.
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