| In north China, dry land covers a large area in the north of Kunlun Mountain, Qinling Mountain and Huaihe River, including 966 counties of 17 provinces, about 56% of area of national territory. The area of cultivated land in this region is approximately 55.4% of national total arable land, and dry land is 73 % of dry land in our country. Considered as one of the most-potential area, It has been an important base of foodstuff production in China with over 85% of the quantity and quality of unused land.However, most part of the aid region's rain fall is 300～500 mm, water resource is no more than 20% of the whole country ,dry and short of water is becoming the main factor that limit the agriculture in these region.Conservation agriculture which using no till or less till is the main technology that could decrease the evaporation and run off, increase the water productivity and water use efficiency. So it's important to research the effect of the conservation agriculture to the soil water content and water productivity.To evaluate potential to improve land and water productivity with adoption of conservation agriculture practices, the DSSAT crop model was calibrated and applied to the dry land agriculture experiment site. We used two crop seasons 2005 and 2006 data from four treatments for calibration. The calibration results gave satisfactory agreement between observed and predicted daily soil moisture contents for all treatments with RMSE in the range of 0.025～0.063, especially in the depth 0～30 cm, the RMSE is in the range of 0.025～0.059. There was satisfactory agreement between field observed and model predicted values for crop yield with differences between observed and predicted values being in the range of 3.1～12% for 2005 and in the range of 2.8～25.2% for 2006, The result of water use efficiency simulation for 2005 is in the range of 1.52～1.78 kg·m-3,NTSM is the highest 1.78 kg·m-3,while in 2006, the range is 1.70～1.71 kg·m-3,the difference is very little. The simulated and observed change of water storage for 2005 is 144.6 mm and 151.7 mm, and for 2006 is 22.9 mm and 46.1 mm.The calibrated model was used for analyzing the long-term changes in crop yield, soil-water balance and for computing the crop water productivity for the four treatments from 1995 to 2004. By adopting conservation agriculture practices, the crop yield be improved by 36%, soil-water storage be increased by 220%, runoff be reduced by 93% and water productivity be improved by 27.7%. Where soil-water storage improvements were low to none, they were compensated for by larger improvements in crop yields and non-beneficial evaporative losses were converted into beneficial transpiration losses. Further, the treatment with residue retention in the range of 0～100% residue cover generated similar increase in crop yield and water productivity compared to the CT treatment.The RRT conservation agriculture treatment was less effective in improving land and water productivities. Thus, adopting NTSM and ASRT treatments are recommended for improving land and water productivity and for reducing soil erosion in dryland regions.
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