The Accumulation Of Nitrate Nitrogen In Soil Profiles In The Semiarid And Semi Humid Area

For utilizing nitrogen fertilizer effectively and reducing the accumulation of residual NO3--N in the soil profile, soil profiles under the different experimental treatments and different soil utilities were collected in Guanzhong of Shaanxi province, Shanbei of Shaanxi province and Dingxi of Gansu province situated in semiarid and semihumid areas,the accumulation intensity of residual NO3--N and influence factor was studied systematically. By research, the results and new viewpoints are as follow: 1. Large quantities of residual NO3--N were accumulated in calcareous soil of semiarid and semihumid agro-ecological system. In all the measured soil profiles, the content and cumulative quantity of NH4+-N was not significant diffference not only in different soil layers but in the soil profile under the different ecological system and management condition, the content is less than residual NO3--N remarkably. The NO3--N accumulative quantity, on average, occupied more than 75% of that of total mineral nitrogen, and it was the principal parts of extracting mineral nitrogen. In the 129 measured soil profiles of Qishan county, there are 26 profiles(0～100cm layers)that its accumulative quantity of residual NO3--N was less than 50kgN/hm2 occupied 20%, the 86 profiles that its accumulative quantity of residual NO3--N was more than 70 kg/Nhm2 occupied 66.7%,the 47 profiles that its accumulative quantity of residual NO3--N was more than 100kgN/hm2 occupied 36% and the 13 profiles that its 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 of one growing season in 0～100cn layers of 66.7% fields at lest; in Yangling, Dingxi county and so on, the content of residual NO3--N in soil profile of most of trial plot, even that of some plots of control plots of no nitrogen application were equal about to the nitrogen uptake of crops of one growing season. These results show fully that the content of accumulative residual NO3--N in calcareous soil profiles of semiarid agro-ecological systems are available nitrogen pool not to be ignored. So residual NO3--N in soil profile must be considered at determining supply capacity of soil nitrogen, or application of nitrogen fertilizer, or the method of determination of soil supply nitrogen index in these areas.2. See from the 100 soil profile samples collected from Guanzhong region, the content and cumulative quantity of NH4+-N are similar to the 129 measured soil profiles of Qishan county, not influenced by soil depth and land utilize. The accumulation of residual NO3--N in soil profile not only in different land utilize but also in same land utilize appeared notable differentia: the residual NO3--N accumulation of 0-100cm in cropland soil profiles changed from 56kgN/hm2 to 1582kgN/hm2; the residual NO3--N accumulation of 0-100cm in orchard soil profiles changed from 93kgN/hm2 to 6791kgN/hm2; the residual NO3--N accumulation of 0-100cm in vegetable land soil profiles changed from 124kgN/hm2 to 3459kgN/hm2. The NO3--N accumulative quantity in orchard or vegetable land soil profiles, on average, occupied more than 75% of that of total mineral nitrogen, but in cropland soil profiles, the NO3--N accumulative quantity , on average, occupied 54%. Because of the applied N fertilizer in orchard or vegetable land soil profiles is much more than that in cropland soil profiles, and the residual NO3--N accumulation of 0-100cm is higher than that in cropland soil profiles, as a result, the proportion of the residual NO3--N accumulation of 0-100cm in orchard or vegetable land soil profiles is higher than that in cropland soil profiles. With the years long, the residual NO3--N accumulation of 0-100cm in orchard appeared increasing trends, the residual NO3--N accumulation of 0-100cm in orchard soil profiles about 5～6 years mostly changed from 287kgN/hm2 to 675kgN/hm2,but to the orchard more than...