Abstract:Winter wheat (Triticum aestivum L.) is the major crop in the North China Plain (NCP). The monsoon climate in this region causes most rain to fall in the summer season, but during the winter-wheat growing season (October-May) the rainfall is far less than the water requirements for the crop. The efficiency of soil water use by winter wheat needs to be improved to reduce the need for irrigation. In this paper, we report the results of two seasons' work on soil water utilization, root growth and distribution, root water uptake by the crop under different irrigation treatments, and possible ways to improve soil water-use efficiency. The field experiments were carried out at Luancheng Station (37°53 0 N, 114°41 0 E) from 1996 to 1997 and 1998 to 1999, two growing seasons of winter wheat. Five treatments for each season: rain-fed and irrigated winter wheat with different irrigation numbers from 1 up to 4, were set up in a randomized plot design. Soil available water-holding capacity at the experimental site was about 454 mm for the top 2 m soil profile. Root sampling results showed that winter wheat had a prolific root system with an average maximum rooting depth of 2 m. Most of the root system was concentrated in the upper 40 cm of soil. Root length density in the top layer of soil (0-20 cm) was very high, with values over 5 cm cm 3 . The distribution of water uptake from the soil profile under high soil moisture conditions was the same as the distribution of root length density. The roots in the top layer of soil played an important role in soil water uptake. When root length density was less than 0Ð8 cm cm 3 , the root was the main factor limiting the complete utilization of soil water by crops. The scarcity of roots in the deep soil layers restricted the full utilization of soil water by the crops. Thus, at maturity, over 100 mm of available water remained in the root zone for the rain-fed treatment, although the upper layers had already entered water deficit. The crop took up 80% of the total available soil water in the treatment without irrigation in a dry season. For irrigated wheat, from 40 to 50% of crop water uptake was from the stored soil water. Available stored soil water played an important role in the higher production of wheat crops in the NCP. Effective measures to increase the utilization of stored soil water could improve crop performance under conditions of limited water supply. Results showed that deep tillage to break the soil pan improved root growth in the deeper soil layers, and sowing the crop evenly also enhanced water uptake from the top soil layer to compete with soil evaporation.

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