添加不同外源氮对长期秸秆还田土壤中氮素转化的影响

【目的】 秸秆还田能够改变土壤中各活性氮库的含量与比例，进而影响土壤氮素供应能力。本文研究了长期秸秆还田条件下添加不同外源氮对土壤中不同形态氮素的影响，旨在明确长期秸秆还田土壤活性氮库的含量差异。 【方法】 长期定位施肥试验点位于湖南省望城县 (112°80′ N、28°37′ E，海拔高度 100 m)。试验开始于1981年，供试土壤为第四纪红色黏土发育的水稻土，轮作制度为稻—稻—冬闲。2014年晚稻收获后，采集单施化肥和长期秸秆还田配施化肥两个处理的耕层土壤样品，开展室内培养试验。每个土壤样品设置灭菌和不灭菌两组主处理，在主处理下设:对照 (CK)、添加尿素 (N 150 kg/hm2，U)、添加秸秆 (N 150 kg/hm2，S) 和添加尿素和秸秆 (N 300 kg/hm2，U + S) 四个副处理，4次重复。在25℃下恒温培养5、10、20、30、50、90、130天时，分析土壤铵态氮、硝态氮、微生物氮和可溶性有机氮含量。 【结果】 1) U、S和U + S处理均显著提高土壤铵态氮和硝态氮含量，高低顺序为U > U + S > S > CK。非灭菌条件下，U处理的土壤铵态氮含量较其他处理高出90.8%～288%。2) 灭菌后土壤铵态氮长期维持在较高水平，其向硝态氮转化过程受阻。在培养90天内，土壤硝态氮、微生物氮和可溶性有机氮含量均处于较低水平。3) 而不灭菌条件下，各处理土壤硝态氮均在培养50 天后迅速增加，至培养结束土壤硝态氮达最大值 (117.43～243.17 mg/kg)。4) 土壤微生物氮和可溶性有机氮分别于培养20天 (106.72～244.01 mg/kg) 和30天 (95.76～140.63 mg/kg) 时达到最大值。5) 至培养结束，灭菌条件下长期NPKS土壤中U + S处理可溶性有机氮显著高于其他处理，较U和S处理分别提高51.55%和29.96%。 【结论】 添加不同外源氮有利于提高长期秸秆还田土壤中活性有机氮的含量，尤其是添加秸秆和尿素处理，能够显著提高土壤氮素的供应能力。

Effect of adding different exogenous nitrogen sources on nitrogen transformation in long-term straw incorporated soil

【Objectives】 This paper was to study the effects of adding different N resources on various N forms in soils long-term applied by NPK with or without straw incorporated, aiming at analyzing the difference in the content of active N pools affected by long-term straw returning. 【Methods】 Surface soil samples from long-term chemical fertilization (NPK) and long-term chemical fertilization with straw incorporation (NPKS) treatments were collected after late rice harvest in 2014 in Wangcheng, Hunan. Indoor incubation experiment was carried out with two main treatments: soil with sterilization and non sterilization onto above-mentioned two kinds of soil samples, respectively. Each main treatment had four subsidiary treatments: the control (CK), application of urea (N 150 kg/hm2, U), application of straw (N 150 kg/hm2, S) and application of urea and straw (N 300 kg/hm2, U + S). Each treatment had four replications. Soil ammonium N (NH₄+), nitrate N (NO₃–), microbial N (MBN) and dissolved organic N (DON) were analyzed at various incubation dates. 【Results】 1) The contents of soil NH₄+ and NO₃– were significantly increased by urea, straw and urea with straw, with a sequence as U > U + S > S > CK. Under non-sterilization condition, soil NH ₄+ of U treatment was 90.85%–288.07% more than those of the other three treatments. 2) Under sterilization condition, soil NH₄+ maintained at a high level, which would hinder the transformation process from NH₄+ to NO₃–. Soil contents of NO₃–, MBN and DON were quite low in the first 90 days of incubation. 3) Under the condition of non-sterilization, soil NO₃– increased rapidly after 50 days of incubation, reaching to the maximal value (117.43–243.17 mg/kg) at the end. 4) Soil MBN and DON reached the maximum value at 20 days (106.72–244.01 mg/kg) and 30 days (95.76–140.63 mg/kg), respectively. 5) At the end of incubation, under sterilization condition, soil DON content of U + S treatment from the long-term NPKS soil was significantly higher than those of the other treatments, with 51.55% and 29.96% more than the U and S treatments, respectively. 【Conclusions】 Adding different exogenous N sources is beneficial to increasing the content of active organic N pool in the soil with long-term straw returning especially adding straw and urea, which would improve soil N supply capacity significantly.