| Nitrogen and water are two key factors affecting crop yield. Therefore, Sustainable agriculture depends to great extent on the efficient use of the limited water and fertilizer resources. Dryland farming is adopted in the north China, where water resource is limited and irrigation is not available. In the north China where irrigation is available, over-application of water and fertilizers is very common. It induces a series of problems. Therefore, using the cultivation methods of semi-dryland farming, i.e., combination of supplemental irrigation method with water-saving methods on dryland farming, is an option for the sustainable utilization of limited water resource in the winter wheat-summer maize rotation system in the region. Dryland and semi-dryland farming has an important role in the agriculture in north China. Therefore, two field experiments conducted in Guanzhong region of Shaanxi Province were used to investigate the effects of different cultivation methods and nitrogen fertilizer rates on nitrogen mineralization and soil water storage and nitrate accumulation in the soil profile and water and nitrogen use efficiency of crop. The main results were:1. A field in-situ incubations method was conducted to investigate the effect of different cultivation patterns and N rate on the soil moisture, temperature, and nitrogen mineralization. In comparison with the conventional cultivation pattern, the plastic mulching and straw mulching patterns significantly increased soil water content in depth of 0-20cm. The plastic mulching also significantly increased soil temperature in depth of 0-10 and 10-20cm; and straw mulching patterns decreased temperature during the incubation period. The application of nitrogen fertilizer significantly increased the content of nitrate in soil, and nitrate leaching from the 0-20cmsoil column in the field. The addition of nitrogen fertilizer also significantly increased the N mineralization of the soil. Straw mulching patterns decreased the N mineralization of the soil. Although the plastic mulching significantly increased soil temperature, it did not increase the soil N mineralization in comparison with the conventional cultivation pattern. Therefore, it is suggested to continue using the in-situ incubations method to study the N mineralization in the field.2. The soil column in situ incubation experiment showed that N mineralization increased during the experiment, and applying nitrogen fertilizer significantly increased the amount and rate of nitrogen mineralization from soil. N mineralized from the soils under the different cultivation models followed the orders of conventional> straw mulching > plastic mulching, whether addition of nitrogen fertilizer or not. For the soil respiration, it followed the orders of straw mulching > conventional> plastic mulching. The N mineralized from soils with laboratory incubation method was about 4.61 to 6.83 times higher than the in-situ incubation method. This related to the favorable moisture and temperature for microbial activity under the laboratory incubation condition.3. A field experiment was conducted in Guanzhong region of Shannxi Province to investigate the effects of different cultivation methods of water saving irrigation and water conservation and nitrogen rates on residual nitrate N in soil profile under winter-summer maize cropping rotation system. Applying nitrogen fertilizer, especially the application of 240 kgN/hm~2, increased the accumulation of nitrate in the soil profile. The nitrate in the soil profile of 240 kgN/hm~2 was about four times of that of 120 kgN/hm~2. The change of nitrate accumulation in the soil profile remained smaller in the 120 kg N/hm~2 nitrogen fertilizer treatment. When the addition of nitrogen fertilizer was increased to 240 kg/hm~2, there were two accumulation peaks (60cmand 160cm) of nitrate in 0-200cmafter the 7th crop harvesting under the conventional, water saving, straw mulching models. For the furrow model, the nitrate acumulative peak was observed at 60cmin soil profile. The accumulative nitrate was found moving to the 200cmand more deep layer. In dry years, furrow, straw mulching and water saving reduced the nitrate in the soil, and followed the order of furrow> straw mulching > water-saving. In wet years, furrow, straw mulching and water saving increased in nitrate residue, and the rate of increase followed the orders of furrow> straw mulching > water saving.4. A field experiment was conducted in Guanzhong region of Shannxi Province to investigate the effects of different cultivation methods on soil water storage, crop yields, efficiency of water and nitrogen. The water storage in soil profile was closely related to the duration of crop cultivation and rainfall during crop growth. Although the furrow, straw mulching and conventional cultivation had some effects on water storage in the 0-2 meters of soil profiles, but the differences were not significant. Applying nitrogen fertilizer significantly increased in the water consumption by crops in 0-2 meters of soil profile, especially in 1-2 m. Nitrogen application significantly increased the grain yield and water use efficiency of maize. However, when the addition of nitrogen fertilizer was increased to 240 kgN/hm~2, crop yields and water use efficiency was not improved. For the different cultivation model, the furrow cultivation model had the highest maize yield and water use efficiency, followed by straw mulching; the conventional mode and the water-saving were lowest. Water use efficiency of maize in dry year (2006) was higher than that in the wet year (2007). With the increase of nitrogen fertilizer, recovery of nitrogen fertilizer, and agronomical efficiency of nitrogen fertilizer and physiological efficiency of nitrogen fertilizer were decreased. Water-saving cultivation method had higher than other cultivations on the effects of recovery of nitrogen fertilizer, and agronomical efficiency of nitrogen fertilizer and physiological efficiency of nitrogen fertilizer.
|
PDF Full Text Request