study the effect of water stress on physiological indices in 3 rice cultivars by(direct planting) under minimum tillage at ahvaz agricultural research center

in order reaching to occurate water regime under minimum tillage system and its effect on the physiological indices of 3 rice cultivars an experiment  was conducted as a split-plot design based on  randomized complete block with three replication in the year of 2006-2007 at research field of shavour station. treatment contains three water regimes with one day or check, two (i2) and three days (i3) interaction for the main factor level and three rice vareties: red anborie (v1) and champa (v2) and ld183 (v3) or danial as a sub factor level.. results of experiment showed that in related to physiological indices humidity stress increases leaf area index (lai), also lai in anburi and champa varieties was more than ld183 variety.in interaction effects between varieties and humidity stresses, combination of following treatments increased lai: anburi variety, humidity stress (, irrigating after 3 days), champa vaiety, humidity stress (irrigating afterdays), ld183, (both kind of humidity stresses). humidity stress by frequency of irrigating after 2 days makes highest crop growth rate (crg), but by increasing of time priority of humidity stress cgr decreased. champa variety has highest cgr between all. in interaction effects between local varieties and humidity stresses cgr decreases by increasing period of humidity stress. but in ld183 rising of humidity stress period, increased cgr.in general humidity stress decreased relative growth rate (rgr) in all varieties. ld183 has highest rgr between all varieties. in interaction effects between varieties and humidity stresses, local varieties show highest rgr when they got irrigated after 3 days but in ld183 humidity stress decreased rgr because of enlarging of lai and increasing of cgr in period of stress condition. net assimilation ratio (nar) decreased at first step of humidity stress condition but in continue at last step of plant growth, nar increased simultaneously by increasing of humidity stress. ld183 had highest nar between all varieties. in interaction effects between varieties and humidity stresses, local varieties show decreasing in nar because of humidity stress.  but nar increased in ld183 varity in condition of irrigating after 2 days and also by enlarging of period of humidity stress nar show falling. so the results indicate that 2 and 3 humidity stresses treatments can be used for rice irrigating.