Abstract: Results from measurements conducted between 1995 and 1998 at Luancheng Research Station showed that leaf water potential, photosynthesis and stomatal conductance of winter wheat, sorghum, millet were maintained in a relatively steady state with soil moisture above a threshold value. Below this critical level, the physiological factors decreased with decreasing of soil water content. Level of this threshold differed in three of the crop varieties studied: in sorghum the critical value was about 42%～45% soil water capacity, millet was at 50 % and in winter wheat the threshold occurred at 60%. Summer corn was slightly different from the other three crops. While stomatal conductance and leaf water potential in this crop varied little across the range of 0.2 to 0.3 volumetric soil water content, photosynthesis increased with increasing soil water content in the same range. The results indicate that corn requires a relatively high water supply for growth and development, while sorghum had the highest drought-resistant ability because of its adaptability to a wider range of soil water contents.

Key words: Crops, Photosynthesis, Stomatal conductance, Leaf water potential, Soil water content