| Water and nutrient are two key factors that affect the crop yields on agricultrue. Sustainable development of agriculture depends to great extent on the efficient use of the limited water and fertilizer resources. Winter wheat-summer maize rotation system is one of major crop rotation system in the north part of our country. This is a very extensive crop rotation system. Farmers usually add more water and fertilizer into their land. The limited agricultural resource (for examples water, fertilizer, heat) is competed between different crops, and leads to the unstable crop yield. Therefore, using the cultivation methods of semi-dryland farming, i.e., combination of supplemental irrigation method with water-saving methods on dryland farming, is a option for the sustainable utilization of limited water resource in the winter wheat-summer maize rotation system in the northern China. Therefore, a field experiment was conducted in Guanzhong region of Shaanxi Province to investigate the effects of different cultivation methods and nitrogen fertilizer rates on biological and grain yields of winter wheat and summer maize in different growth stages; nitrogen accumulation, distribution of winter wheat in different growth stages; water storage and water use efficiency and residual nitrate N in soil profiles. The main conclusions include:1. Application of nitrogen fertilizer increased the biological and grain yield of winter wheat significantly. However, while the nitrogen application was increased from 120 kg/hm2 to 240 kg/hm2, the biological and grain yield of winter wheat didn't keep increasing. Compared to the application of nitrogen fertilizer, the effects of different cultivation methods on the biological yield in winter wheat at the different stages was not significant, and the effect was different with different wheat growth stages. Compared with four cultivation methods, from jointing stage to filling stage, the biological yield of furrow planting was the highest; the biological yield of straw mulching was the highest from filling stage to mature stage. Application of nitrogen fertilizer can increase the biological and grain yield of summer maize, but not reach significant level. The biological yields of both furrow planting and straw mulching was higher than that of conventional and water-saving cultivation methods. With the maize growth prolonging, this trend became smaller and smaller. 2. In comparison with the application of nitrogen fertilizer, the effects of different cultivation methods on nitrogen accumulation and distribution in winter wheat at the different stages were not significant. Compared to other three cultivation methods, the nitrogen residue in the leaf and stem of wheat after harvesting and the rate of residue N to total N accumulation were lower in supplementary irrigation pattern; however, the ratio of the nitrogen residue in the grain to the nitrogen accumulated in shoot was increased. As the increasing of the application rates of nitrogen fertilizer, nitrogen accumulation in the leaf, stem, glume and rachis and grain of wheat was significantly increased. When the nitrogen application was increased from 120 kg/hm2 to 240 kg/hm2, nitrogen accumulation in wheat leaf, stem and glume & rachis was increased after harvesting respectively; however, there was significantly increase in wheat grain. The application of nitrogen fertilizer had no significant effect on the distribution of N in different organs of wheat. As the increasing of the application rates of nitrogen fertilizer, there was a decreased trend on nitrogen recovery, agronomic efficiency and physiological efficiency. Compared with other different cultivation methods, N recovery, N agronomic efficiency and N physiological efficiency of supplementary irrigation pattern were higher during the two continuous years; the changes of these nitrogen efficiency indices of the other three cultivation methods were various in different years.3. With the winter wheat growth prolonging, there was a decreased trend on the water storage in 0-100 cm depth of soil under different cultivation methods. In addition, different cultivation methods had different effects on water storage and conservation, the order was furrow planting>straw mulching>conventional and water-saving cultivation methods. However, the difference of water storage was not significant in 0-100 cm depth of soil under different cultivation methods during summer maize growth, because the stage of summer maize growth was the rainy season of this region. With the planting stage prolonging, the water storage had significant trend in 0-200 cm depth of soil under different cultivation methods, the order was furrow planting>straw mulching>conventional and water-saving cultivation methods. As the increasing of the application rates of nitrogen fertilizer, the water storage became fewer and fewer, and the water storage was significant decreased in 100-200 cm of soil after winter wheat harvesting. In some extent, with the increasing of the application rates of nitrogen fertilizer, the grain yield and water use efficiency of winter wheat and summer maize were increased. Grain yield and water use efficiency of winter wheat was the highest under straw mulching, the next was furrow planting, and the conventional and water-saving cultivation methods were the smallest. However, Grain yield and water use efficiency of summer maize was the highest under furrow planting, the next was straw mulching, and the conventional and water-saving cultivation methods were the smallest.4. After the fifth crop harvesting stages, the mean residual nitrate N of 0-200 cm depth of soil under different cultivation methods was from 218 kg/hm2 to 329 kg/hm2, most of them was found in 100-200 cm depth of soil. Compared to other different cultivation methods, the residual nitrate N in 0-200 cm depth of soil under the furrow planting system was the highest. With the increase of cultivating seasons and the increasing application rates of nitrogen fertilizer, the rate of residual nitrate N in soil was significant increased. The residual nitrate N in 0-200 cm depth of soil was about 477 kg/ hm2 at the fifth crop harvesting with the nitrogen rate was 240 kg N/hm2. The ratio of increased residual nitrate N to the application rate of nitrogen fertilizer was 51.6% from the third harvesting to the fifth harvesting. After the fifth crop harvesting, the amount of nitrate accumulation in 0-80 cm soil profiles under conventional, water-saving and straw mulching cultivating methods was lower. However, the amount of nitrate accumulation under 80 cm depth of soil increased significantly when the application rate of nitrogen fertilizer was increased. The amount of nitrate accumulation in 0-200 cm soils was increased significantly with the application rate of nitrogen fertilizer increased under the furrow planting cultivating method, and it was higher in 0-120 cm soil profiles than other cultivating methods.
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