| The sustainable development of dryland farming is important for food, ecological and resource security in the world. The production of dry farming is to great extent depdendent on the precipitation and its use technical measures. In the agro-ecosystems, applying nitrogen fertilizer is a key tool to increase the crop yield. However, many problems, for example, limited funds and resources waste and environmental pollution, limit the application of nitrogen; as a result, it affects the sustainable agricultural development. In this study, field experiment was used to study the effects of the different cultivation methods used on the dryland, including the conventional cultivation method (without any mulching methods), plastic mulching and straw mulching patterns, on the spatial-temporal variation of water and mineral nitrogen in soil; and three methods of laboratory incubation, field in-situ incubation and field nitrogen balance were used for measuring soil nitrogen mineralization under different cultivation patterns in dryland. The main results were as follows: 1. During the growth period of March to May, water content of 0~20 cm soil layer significantly fluctuated. The order of water content was: 0~5 cm>5~10 cm>10~20 cm.Compared to the conventional cultivation method, plastic mulching and straw mulching significantly increased the water content in soil depth of 0~5, 5~10 and 10~20 cm; However, the application of nitrogen fertilizer decreased the water contents in the above soil depth. The effects of different cultivating methods on the water contents in 0~100 cm soil depth varied with the growth period of winter wheat. The water contents in 0~100 cm soil depth under plastic mulching and straw mulching cultivation was significantly higher than that of the conventional cultivation method at reviving stage; at the shooting stage, the water contents in 0~100 cm soil depth under straw mulching cultivation was significantly higher than that of the plastic mulching cultivation method; and there were not significant differences on the water content in 0~100 cm soil profile among the different cultivating methods at the grain-filling stage. The level of NH4+-N in soil of different treatments remained at a very low level during the whole growing period of winter wheat, while the variations of NO3--N content in soil was very high. The spatial-temporal variations of soil NO3--N had close relationships with N application level, cultivation methods and growth stage. The content of NO3--N and the accumulation of mineral nitrogen in 0~20 cm soil increased with the increase of N rate added, and decreased as the growing of winter wheat. The accumulation of NO3--N in 0~100 cm soil were in the following order, straw mulching >normal cultivation >plastic mulching.2. In-situ soil column incubation showed that the content of NO3--N, mineralized nitrogen and mineralization rate of the different treatments had an increased trend during the incubation. Compared to different cultivating patterns, the order was plastic mulching > straw mulching> conventional cultivation. Different mulching, layers and nitrogen rate had little effect on NH4+-N. The amount of mineralization and mineralization rate in April were higher than that in March. Plastic mulching significant increased water content and accumulated temperature in 0~20 cm soil. Straw mulching can stabilize soil temperature in each day. Soil moisture and accumulated temperature in soil at 14:00 reduced with the deeper of soil layer; but it was controversy at 8:00. Coefficients analysis showed that there was no significant correlation between soil net N mineralization, NO3--N, NH4+-N, soil moisture and soil accumulated temperature, which is perhaps related with the great variation of soil characteristics in the field.3. Laboratory incubation experiment showed the amount of mineralization with the no nitrogen treatment was in the following order, straw mulching > conventional cultivation > plastic mulching. There was significant difference in different soil layers of different cultivating patterns with nitrogen treatments. With soil depth deeper, NO3--N, nitrogen mineralization and mineralization rate tended to reduce. The content of NO3--N, amount of mineralization and mineralization rate of conventional cultivation and plastic mulching patterns in the day of 14 to day 28 were lower than that in the incubation of day 0 to day 14, and an opposition trend was found in straw mulching pattern.4. After harvesting one season of winter wheat, water contents in 0～200 cm soil depth reduced significantly. The highest water consumption was found in plastic mulching, but the least in straw mulching. Application of nitrogen fertilizer increased the water consumption. Wheat yield, biomass, plant N uptake and water use efficiency were increased in the mulching and application of nitrogen fertilizer. Soil net N mineralization was different in the different cultivation patterns. Mulching was favorite for soil nitrogen mineralization; average nitrogen mineralization rate was 4.55 kg hm-2 per month, and the order was plastic mulching > straw mulching > conventional. Coefficients analyses showed the significantly positive correlation of soil net N mineralization bewteen wheat biomass was existed.5. For the three soil nitrogen mineralization methods, the nitrogen mineralization rate was in the following order, laboratory incubation > field nitrogen balance > in-situ incubation. The average mineralization rate of laboratory incubation was as 3.55 times as that in-situ incubation, which is related with the laboratory incubation methods could provide feasible moisture and temperature for the mineralization. Under field conditions, the greatly spatial variability of soil nitrogen mineralization was an important factor which affects the accuracy results in-situ incubation.
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