In order to seek the optimal soil moisture index during the
coexistent period,the study was carried out from Oct 2003 to
Jun 2005.The main physiological characteristics of wheat and the growth potential of cotton were determined and the soil water
consumption of wheat and cotton were estimated during the
coexistent period of wheat and cotton.The results showed that,with the proceeding of coexistent period,the flag leaf water potential,stomatal conductance,apparent quantum yield,net photosynthetic rate and transpiration rate of wheat were all declined,but rose with the increase of soil moisture with the obvious differences among treatments.The differences of transpiration rates among different treatments were rapidly minified along with the growth proceeding and the senescence of wheat.With the soil moisture increased,the whole soil water consumption of crops,and that of wheat or cotton rose obviously.The soil water consumption during coexistent period accounted for 28.8%-30% of that of wheat whole growing period.The wheat soil water consumption was(67.9%)-72% of that of crops during the coexistent period.The wheat water use efficiency of the treatment of 60% relative soil moisture(the water-holding capacity of the experiment field was 24%) was the highest up to 1.63 kg/m~3 with no obvious decline of wheat yield and the highest sturdy index of cotton seedlings,while wheat yield slightly increased under the condition of 70% soil moisture treatment with the lower water use efficiency of 1.45 kg/m~3 and the lower sturdy index of cotton seedlings.The study confirmed that during the coexistent period of wheat and cotton in huanghuaihai plain,the optimal soil moisture should be 60%-70%.