土壤学报2017，Vol.54Issue(5)：1230-1239,10.DOI:10.11766/trxb201704120060
黄土高原旱地夏季休闲期15N标记硝态氮的去向
Fate of 15N Labeled Nitrate in Dryland under Summer Fallow on the Loess Plateau
摘要
Abstract
[Objective]Summer fallow after winter wheat is harvested in dryland on the Loess Plateau is a very common practice to save rain water,and restore soil fertility for the next crop. Nowadays,the content of nitrogen(N)(mainly in nitrate form)in the soil of the dryland as residue of the fertilizer applied to winter wheat is increasing steadily. As summer is the rainy season in this region,whether or not the high rainfall would increase NO3--N leaching loss is an important issue deserving further study. The method of adding 15N labeled nitrate after winter wheat is harvested in dryland is one to quantitativelyexplore fate of the residual fertilizer N in the dryland under summer fallow in the Loess Plateau,and hence to provide a scientific basis for managing Nin dryland.[Method]The 15N labeled fertilization micro-plot(Polyvinylchloridecolumn,25 cm diameter and 25 cm long)method was used to study fate of the residual fertilizer N in the dryland under summer fallow in a field experiment,which hadfive tracts of cropland and two N treatments set up with and without N application(0 and 30 kg N hm-2). 15N labeled nitrate was mixed with the surface soil(0~15 cm)in the micro-plot at a rate equal to the content of the residual fertilizer N in the field after winter wheat was harvested. At the end of the summer fallow,soil samples throughout the soil profile(0~200 cm)were taken fromthe micro-plots,for analysis the contents of soil total nitrogen,NO3--N,and their 15N abundance.[Result]Results show that at the beginning of the summer fallow,the content of NO3--N accumulated in the 0~200 cm soil was quite high,ranging between 205 and 268 kg hm-2 and averaging 244 kg hm-2;At the end of the summer fallow,apparent NO3--N accumulation peaks were found in the soil,40~80 cm in depth,and 15N abundance ranged between 0.408% and 0.482% and averaged 0.429%,being the highest in the soil 60 cm in depth,averaged 0.372% in the soil 80 cm in depth,being higher than the background value of 15N abundance in the soil(0.36715N atom%),and was 0.369 % in the soil 100 cm in depth,more or less the same as the background value,in Treatments N30 in all the five tracts of cropland. In the five tracts of cropland,15N labeled nitrate abundance was the highest in the 40~60 cm soil layer in the soil profiles (0~100 cm),averaging 2.151%;and the lowest abundance was in the 80~100 cm soil layer,averaging 0.407%,both significantly higher than the background value. Although the rainfall during the summer fallow season was only 157 mm,making it a dry year,it still leached 15N labeled nitrate down to 80 cm in depth, through a 45~65 cm thick soil layer,and even 15N labeled nitrate was found in 100 cm depth. At the end of the fallow,the content of residual N averaged 21.6 kg hm-2 or ranged between 20.8 and 22.9 kg hm-2 in the 0~100 cm soil profile,accounting for 71.9% of the applied N fertilizer in all the five tracts of cropland. The content of residual labeled N was 4.5 kg hm-2,2.9% of which was in the form of NO3-- N in the 0~20 cm soil layer;Residual fertilizer N was mainly distributed in the 40~60 cm soil layer,and averaged 17.7 kg hm-2 in content,accounting for 52.8% of the total N fertilizer applied,in which 15N labeled nitrate content was 6.8 kg hm-2. After the summer fallow,the applied 15N labeled N fertilizer was found lost at a rate of 23.8%~30.8%(averaging 28.1%).[Conclusion]Residual fertilizer N accumulated significantly in the 0~200cm soil layer of the dryland after wheat was harvested,posing a potential risk of leaching. In 2014, though it was a dry year,the effect of rain water leaching NO3--N was still quite significant,indicating that the NO3--N leaching in the dryland during the summer fallow season should not be ignored and further studies should be done on mechanisms of its leaching loss.关键词
旱地/夏季休闲/15N标记法/残留肥料氮/硝态氮淋溶Key words
Dryland/Summer fallow/15N labeled fertilization method/Residual fertilizer N/Nitrate leaching分类
农业科技引用本文复制引用
夏梦洁,陈竹君,刘占军,周建斌..黄土高原旱地夏季休闲期15N标记硝态氮的去向[J].土壤学报,2017,54(5):1230-1239,10.基金项目
国家自然科学基金项目(31372137)资助 Supported by the National Natural Science Foundation of China(No. 31372137) （31372137）
