基于1978年开始的陇东旱塬定位试验,分析雨养条件下麦田0~100 cm剖面土壤氮素状况.设计6种试验处理:不施肥、氮肥、氮磷肥、氮磷配施秸秆、有机肥、氮磷配施有机肥.结果表明:有机肥、氮磷配施有机肥处理改善土壤氮素肥力效果优于其他施肥措施,0~40 cm土层全氮、碱解氮、无机氮含量均显著增加,其中0~20 cm土壤全氮较36年前平均提高了26.2%;氮磷配施秸秆处理土壤全氮及碱解氮显著高于对照,全氮与试验前持平或略有提升;氮肥、氮磷肥处理的耕层土壤全氮较试验前分别降低了13.1%和6.4%.氮肥处理深层土壤硝态氮明显较高,其他各施肥处理均能减少硝态氮下移.不同施肥处理改变了土壤的无机氮构成,有机肥与秸秆的作用有较大差异.结果说明不同施肥显著影响农田土壤氮素状况,施用有机肥是培育土壤氮库、而无机氮磷肥配合及有机无机配施是减少NO3--N下移的有效手段.%The Loess Plateau of East Gansu is a typical area where rainfed farming prevails. To understand effects of long-term fertilization on soil nitrogen in soil profile is something very meaningful to farmers in doing fertilization in this area and to researchers in enriching scientific knowledge of soil nitrogen nutrition as well. From wheat fields of a long-term fertilization experiment that started in 1978 and had six treatments,i.e.,no fertilizer(CK),nitrogen only(N),nitrogen and phosphorous(NP),nitrogen and phosphorous combined with straw return(SNP),manure only(M),nitrogen and phosphorous combined with manure(MNP),soil samples were collected during the booting and summer fallow stages of wheat in 2014 for analysis of soil total nitrogen(total-N),soil available nitrogen(ava-N),soil mineral nitrogen (min-N)and composition of min-N. Results showed that treatments M and MNP obviously improved soil nitrogen nutrition and were significantly higher than the other treatments in total-N,ava-N,min-N in the 0~40 cm soil layers. No big difference in soil total-N was found between the two treatments. They both increased soil total N by 26.2% on averagely in the 0~20 cm soil layer over the original value in the year of 1978 when the experiment started. Treatment SNP was higher in total-N and ava-N than CK but significantly lower than treatments M and MNP. However,total-N in treatment SNP remained almost the same as or was just slightly higher than the original value. Though treatment NP was quite low in total-N and ava-N,it was still higher than treatments N and CK. Treatments N and NP were 13.1% and 6.4%,respectively,lower than the original value in total-N of the 0~20 cm soil layer. The treatments did not vary much in absolute value of NH4+-N concentration in the soil profiles,but treatment N stood out in NO3--N concentration throughout the 0~100 cm soil profile,while the other treatments were higher in the topsoil and sub-topsoil layers than in the 40~100 cm or 60~100 cm soil layer. All the fertilization treatments,particularly treatments M and MNP, lowered NH4+-N/NO3--N ratio in the topsoil layer. Treatment SNP tended to increase the proportion of NH4+-N in soil total N and hence NH4+-N/NO3--N ratio in the middle and lower soil layers. The phenomenon was getting more significant with soil depth in the profile during the summer fallow season. To sum up,under rainfed farming in the Loess Plateau of East Gansu,the practices of applying NP in combination with organic manures are superior to the others in building up soil fertility. The application of N or NP only fails to maintain balance of total-N in the soil. The application of chemical nitrogen alone aggravates downward leaching of NO3--N, while the practices of manure,NP and NP plus manure application are proved to be able to reduce NO3--N leaching. However,NH4+-N is not much affected by fertilization practices. Fertilization changes composition of min-N,but the effects of manure application and straw incorporation differ quite sharply. It is,therefore, suggested that more efforts should be dedicated to the study on fate and transformation of soil nitrogen under rainfed farming in future.
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