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404 S. Boonpradub, M. Chatasiri alld N. Senanarongused. Results indicated that the 7- days irrigation interval was 7 % greater grain yield than the 14­days irrigation interval but they were not significantly different. The yield of hand weeding at 2 and4 weeks after emergence provided a significantly 55 % higher grain yield than the unweededtreatment, however, it was not significantly different when compared to hand weeding at 2 weeks.Yield components, agronomic characters and weed dry weights were also affected by irrigation andweed control treatments (Table 5).Table 5 Grain yield at 14 % moisture content and yield components of DK 888 grownafter rice under different irrigation frequency and weed control at PSL FCES in1996.WeedGrain Plant Ear Ear Ear DWTreatment yield height length width number at 1(t ha,l) (cm) (em) (em) (ha) month(g/mI\2)Irrigation Frequency- 7 - days interval 5.15 a* 181.9a 17.8 a 4.0 a 49,266 a 74.4- 14 - days interval 4.68 b 161.2 b 17.5 a 4.0 a 47,866 b 69.6Weed Control- Unweeded 3.78 c 160.1 d 17.3 b 3.9 b 41,733c 123.6 a- Pre-emergence herbicide 4.50 b 171.0 c 17.6ab 3.9 b 45,600 b b- Hand weeding at 2 wks 5.83 a 182.4 a 17.5 b 4.1 a 54,933 a c- Hand weeding at 4 wks 4.52 b 167.7 c 18.0 a 3.9 b 46,933 b ab- Hand weeding at 2,4 wks 5.89 a 178.4 b J7.7 ab 4.1 ab 54,000 a 20.8 c- Pre-emerg. + handweeding at 4 wks 4.96 ab 169.7 c 17.7 ab 4.0 a 48,066 b 93.6 abC.V.(%) 11.1 2.3 1.6 1.7 6.8 38.6* Values within a column followed by the same letter are not significantly different at the 5 % levelof probability using DMRTTillage System and Water DeficitTillage improves soil aeration and provides a good physical seedbed condition for plantgermination and growth. However, it accelerates soil moisture loss and also increases costs and time(Sanchez.1976). On the other hand, no-tillage cultivation is one of the conservation tillage which canbe effective not only for increasing soil and water conservation but also for reducing laborrequirement and time (Unger and McCalla,1981). Higher yields of maize when grown under notillagesystem in rainfed areas have also been reported in Thailand (Na Nagara et af.,1984; Tongyaiet af., 1980).Two maize cultivars differing in maturity were planted on sandy loam texture under differenttillage system and water stress. A split - split plot design with three replication was used. Yield ofmaize as shown in Table 6 illustrated that the tillage system treatments were not significantlydifferent. The reduction of maize yield was 35 and 20 % when grown under severe stress (waterdeficit from V9 until physiological maturity) and mild stress (water deficit from R I until