| For effectively utilizing nitrogen fertilizer and reducing the accumulation of residualNO-3-N in soil profile, the accumulation of residual NO-3-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 NO-3-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 NO-3-N. The NO-3-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 NO-3-N was less than 50 kg N/hm2occupied 20%, the 86 profiles whose accumulative quantity of residualNO-3-N was more than 70 kg/Nhm2occupied 66.7%, the 47 profiles that its accumulative quantity of residual NO-3-N was more than 100 kgN/hm2occupied 36% and the 13 profiles whose accumulative quantity of residual NO-3-N was more than 140 kg/Nhm2occupied 10%, the nitrogen uptake of crops of every growing season was about 70 kg/Nhm2. These results indicated that the content of residual NO-3-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 NO-3-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 NO-3-N in calcareous soil profiles of semiarid agro-ecological systems were available nitrogen pool not to be ignored. So residual NO-3-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 NO-3-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 NO-3-N accumulation in 0～1 000 cm soil layers was respectively 1 295.6 kgN/hm2and 710.4 kgN/hm2, that in 0～600 cm soil layers was respectively 706.1 kgN/hm2and 435.0 kgN/hm2, a large amount of NO-3-N was accumulated under 200 cm soil layers in two observed soil profiles, the amount of NO-3-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 NO-3-N accumulation in 0～200 cm soil layers. This indicated that the added NO-3-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 NO-3-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 NO-3-N in soil profiles and the plot of no nitrogen fertilizer application was bigger when nitrogen fertilizer was successively applied, especially applying the high rate of nitrogen fertilizer; In the long-term experiment of Yangling in 25 years, the amount of residual NO-3-N accumulation of 0～120 cm layer in the treatment of N+P was 163.4 kgN/hm2increased by 111.6 kgN/hm2compared with CK of no fertilization 51.8 kgN/hm2, If combining N+P treatment with fallow, the effect of increasing of residual NO-3-N was more significantly and increased by 156.5 kgN/hm2compared with the CK. The experiment also showed that the amount of residual NO-3-N accumulation could be reduced to some extent if combined N+P treatment with corn straws, and the amount of NO-3-N accumulation decreased with increasing of the amount of corn straws, compared with CK of no nitrogen fertilizer application, the residual NO-3-N couldn't accumulate when the rate of nitrogen fertilizer application in every season was low through successive nitrogen fertilizer application for crops in 4 慳捥捡畳浯畮汳愠瑩敮搠?楨湥?瑧档敨?獮潧椠汣?灵牮潴晹椻氠敢獵???晨瑥攠牣?睮桴敥慮瑴?桯慦爠癲敥獳瑩??牡慬椠湎晏愼汳汵?椾猭?愯汳獵潰￣瘼敳牵祢￣爳椼振桳??猾漭?爠敡獣楣摵畭慵汬?乴佥?猠畩灮????猲田瀠??猠畳扯????獡畹扥??丠?睮慣獲?敡慳獥楤氠祳?汧潮獩獦敩摣?瑮桴牬潹甠杷桨?汮攠慴捨桥椠湲条?慥渠摯?搠敮湩楴瑲牯楧晥楮挠慦瑥楲潴湩??智牥潲洠?瑰桰楬獩?灡潴楩湯瑮?潷晡?瘠楧敨睥??灴汨慡獮琠椱挱′昮椵氠浫?济甯汨捭格楳湵杰￣昲漼爯?瑵桰放?睔桨潥氠整?杯爠潦睩楥湬杤?灥數牰楥潲摩?獥桮潴畳氠摩湮?瑙?扮敧?慩摮癧漠捳慨瑯敷摥?椠湴?瑡桴攬?捩畮氠瑴畨牥攠?潥晡?睳栠敥慩瑴?er of enough rainfall or arid, fallow can significantly increase the quantity of residual NO-3-N in soil profiles, and the content of NO-3-N in 100～200 cm layers of fallow plot was higher than that in multiple corn plots, so multiple corn could reduce the content of residual NO-3-N accumulation in soil profile. Film mulching must relate to the soil nitrogen transformation processes which have significant relationship with soil biological process, thus it also affected the accumulation of residual NO-3-N in soil profile. The results of 2-year experiment in which spring wheat was used as indicating crop showed that plastic film mulching for the whole growing period after harvest could significantly increase accumulation of residual NO-3-N in soil profiles after harvest; it increased by 9.4 kgN/hm2in 1999 and 17.9 kgN/hm2in 2000 under no nitrogen fertilizer application condition; it also increased by 88.9 kgN/hm2in 1999 and 39.9 kgN/hm2in 2 000 under nitrogen fertilizer application condition; but plastic film mulching at the former growth stage and no mulching at the latter growth stage had advantage to reduce the accumulation of residual NO-3-N in soil profiles. At the latter growth stage, soil water condition in tilth layers was better and temperature was higher, so it also was beneficial to the mineralization of soil organic nitrogen, but at this stage, the uptake power of wheat to NO-3-N became weak and the requirement of NO-3-N became low, therefore, the amount of residual NO-3-N was |