【摘要】 为了有效利用氮肥,减少残留NO3--N在土壤剖面中的累积,在位于半干旱半湿润地区的陕西岐更多还原

【Abstract】 For effectively utilizing nitrogen fertilizer and reducing the accumulation of residualNO₃^--N in soil profile, the accumulation of residual NO₃^--N was studied systematically in Qishan, Yangling, Chengcheng of Shaanxi province and Dingxi of Ganshu province situated in semiarid and semihumid areas. In these experiments, the soil profiles under the different experimental treatments were collected. The results showed that quantities of residual NO₃^--N were accumulated in calcareous soil of semiarid agro-ecological system. In all the measured soil profiles, the aontent and cumulative quantity of NH₄⁺-N was not significantly diffferent not only in different soil layers but in the soil profiles under different ecological systems and management conditions, its content changed from 1 to 3μgN/g and the accumulative quantity was from 14 to 42 kgN/hm², averaging 28 kgN/hm², and the accumulative quantity was significantly less than that of NO₃^--N. The NO₃^--N accumulative quantity, on average, occupied more than 75% of that of total mineral nitrogen, and it was the principal parts of extracted mineral nitrogen. In the 129 measured soil profiles of Qishan county, there were 26 profiles（0～100 cm soil）whose accumulative quantity of residual NO₃^--N was less than 50 kg N/hm² occupied 20%, the 86 profiles whose accumulative quantity of residualNO₃^--N was more than 70 kg/Nhm² occupied 66.7%, the 47 profiles that its accumulative quantity of residual NO₃^--N was more than 100 kgN/hm² occupied 36% and the 13 profiles whose accumulative quantity of residual NO₃^--N was more than 140 kg/Nhm² occupied 10%, the nitrogen uptake of crops of every growing season was about 70 kg/Nhm². These results indicated that the content of residual NO₃^--N was equal to nitrogen uptake of crops in one growing season in 0～100 cm soil of 66.7% fields at least; in Yangling, Chencheng, Dingxi county and so on, the content of residual NO₃^--N in soil profiles of most trial plots, even that of some plots in control plots of no nitrogen application were about equal to the nitrogen uptake of crops in one growing season. These results showed fully that the content of accumulative residual NO₃^--N in calcareous soil profiles of semiarid agro-ecological systems were available nitrogen pool not to be ignored. So residual NO₃^--N in soil profile must be considered in determining supply capacity of soil nitrogen, or application of nitrogen fertilizer, or the method of determination of soil supply nitrogen index in these areas. The residual NO₃^--N of soil profile gradually moved to the deep layers through convection and diffusion and so on, gotten out of root region. The determined results in the Vegetable Experimental Station and Irrigation Experimental Station showed that the content of NO₃^--N accumulation in 0～1 000 cm soil layers was respectively 1 295.6 kgN/hm² and 710.4 kgN/hm², that in 0～600 cm soil layers was respectively 706.1 kgN/hm² and 435.0 kgN/hm², a large amount of NO₃^--N was accumulated under 200 cm soil layers in two observed soil profiles, the amount of NO₃^--N accumulation in 200～400 cm, 400～600 cm, 600～800 cm and 800～1 000 cm soil layers were significantly higher than that of NO₃^--N accumulation in 0～200 cm soil layers. This indicated that the added NO₃^--N in surface soil by all the ways could completely take off root region and leach to the soil layers under 1 000 cm through long-term leaching. All the trial results in different experimental areas showed that, compared with plots of no nitrogen fertilizer application plot, the contents of accumulative residual NO₃^--N in nitrogen fertilizer application plot soil appeared increasing trends when crops were harvesting, and it increased with the rate of nitrogen fertilizer application. The long-terms experiment in Yangling and Chengcheng showed that the difference between residual NO₃^--N in soil profiles and the plot of no nitrogen fertilizer application was bigger when nitrogen fertilizer was successively applied, especially applying the high r更多还原