Study on the incorporation of rice straw to increase organic matter for paddy soil in northeastern and northern parts of Thailand   Pracha Nakapraves Preede Deerugsa Pityakorn Limthong Valvta Vasananukool Puntipa chaiyana Kirkkieat Greepjumpa   ABSTRACT         Study on the incorporation of rice straw to increase organic matter for paddy soil in northeastern and northern parts of Thailand was conducted in Farmer's area, Tambon Nongwaeng Nagbao, Amphoe Pol, Khon Kaen Province and in the area of Chiang Mai Development Station, Amphoe Maerim, Chiang Mai Province, in Roi Et series and Renu series respectively during 1989-1993. The Randomized completed block Design was used composing of 6 treatments and 4 replication which were incorporation 500 kgs/rai of burned rice straws, incorporation 500 kgs/rai of rice straw, incorporation 1,000 kgs/rai of rice straw, incorporation 1,500 kgs/rai of rice straw, incorporation 2,000 kgs/rai of rice straw and, incorporation 2,500 kgs/rai of rice straw. The results were obtained in Roi Et series that the RD 23 high, tillering and numbers of panicle/tiller were not significantly different, but the straws weight and yield of RD 23 had shown significantly different that incorporation of rice straw from 2,000 to 2,500 kgs/rai could produce highly rice straws weight and rice yield. In Renu series, there were not significantly different of rice high, tillering, number of panicle/tiller and rice straw weight also but the yield of RD 23 responsed to the incorporation of rice straws rating from 2,000 to 2,500 kgs/rai. Therefore, it could be concluded that the incorporation in high rate of rice straws from 2,000 to 2,500 kgs/rai would give highest of RD 23 rice yield.         Keywords : rice straw, panicle