study on effect of humidity stress on phisiological indices of 3 rice vareties by( direct planting) in condition of minimum tillage in ahvaz agricultural research center

in order reaching to occurate water regime in the condition of minimum tillage and its effect on the yield and yield component physiological index of rice varieties, a experiment had carried out the agronomey year of 2006-2007 in the research field of shavour station. the experiment had carried out in split-plot design some randomized complete block with three replication that contains three water regimes with one day or check, two (i2) and three days (i3) interaction for the main factor level and three rice varieties: red anborie (v1) and champa (v2) and ld183 (v3) or danial as main factor level. results of experiment show that in 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.