设施菜地水旱轮作氮素环境效应及N2O排放机制

Greenhouse soil degradation is one of the restricted factor for sustainable development of the vegetable productions in China,paddy-upland rotation is one of the effective agronomic measures to solve this problem. However,it will be brought some negative influences on the environment,while solved the problems in the vegetable production.Therefore,the research of nitrogen environmental consequences and the mechanism of N2O emission in greenhouse vegetable field under paddy-upland rotation was conducted.In this study,field experiment was carried out to investigate the nitrogen leaching,N2O emission and the characteristics of the annual dynamic changes,to evaluate the environmental negative influence degree on paddy-upland rotation.Using 15N tracing technique and a 15N tracing model,the N2O productions of which nitrogen transformation processes from waterflooding soils were investigated,which to quantify the contributions of autotrophic nitrification, heterotrophic nitrification,and denitrification to N2O production from the greenhouse vegetable fields.Soil incubation experiments were conducted to explore the mechanism of N2O production increasing,to study the relevance of the N2O production,the N2O/(N2O+N2) product ratio and soil inorganic nitrogen content (NH4-N, NO3-N and NO2-N) and soil pH,EC and Eh.Ultimately,to provide the scientific basis for the continuous extending of the paddy-upland rotation in greenhouse vegetable systems and the corresponding measures to reduce the emission was proposed.

设施土壤的退化是限制我国设施蔬菜可持续发展的重要因素，而进行水旱轮作是解决此问题的农艺措施之一。然而，水旱轮作在解决生产问题的同时会对环境造成一定的负面影响。本项目针对水旱轮作的氮素环境效应和N2O排放机制开展研究。通过田间小区试验，观测设施菜地水旱轮作下氮素淋洗和N2O排放及其周年动态变化特征，评价水旱轮作对环境的负面影响程度；采用15N培养试验，结合数值分析方法，研究设施土壤淹水后氮的不同转化过程（自养硝化、异养硝化和反硝化过程）对N2O的贡献和不同转化过程N2O的产生比率，阐明设施菜地土壤淹水后N2O主要的产生过程；通过室内培养试验，研究设施菜地土壤N2O的产生、N2O占（N2O+N2）的比例与土壤无机氮（铵态氮、硝态氮和亚硝态氮）含量以及土壤pH、EC、Eh的关系来探索其N2O产生量增加的机制。最终为设施蔬菜种植体系水旱轮作的持续推广以及相应的减排措施的提出提供科学依据。

针对设施菜地土壤氮肥利用率低、次生盐渍化严重的问题，探索传统菜菜轮作制度调整为菜稻轮作制度对提高氮肥利用率、减轻次生盐渍化的可行性及其机制，评估其环境效应，以实现设施土壤的可持续利用。本研究采用田间小区试验，设置了3个施氮水平：不施化肥氮（0%N）、农户习惯施氮量（100%N）、农户施氮量下减施N 40%（60%N），并分别采用3种轮作制度番茄--莴苣--芹菜（Rv）、水稻--莴苣--芹菜（Rr）和番茄--水芹--水芹（Rc）轮作，进行了连续2年的试验，观测设施菜地水旱轮作下N2O排放及其周年动态变化特征，评价水旱轮作对环境的负面影响程度；采用好气土壤培养试验，开展了设施菜地土壤淹水后N2O的排放规律以及N2O排放增加的机制研究。.结果表明，习惯施N量下，Rc轮作的蔬菜产量显著高于Rv轮作和Rr轮作，且其经济效益最高；减施40%的化肥N不会影响蔬菜产量。传统旱地蔬菜进行水旱轮作后可显著降低土壤EC，可降低1-2倍；土壤pH可升高16-19 %，有效改善土壤理化性状。习惯施N量下，Rc轮作对环境可造成较负面影响，显著增加N2O排放和氨挥发排放；次生盐渍化的设施土壤种植水稻，不会增加氨挥发排放，水稻种植第1年可显著增加N2O排放，第2年N2O排放不再增加；但Rr轮作的经济效益最低。轮作制度调整对土壤细菌群落结构产生了影响；与传统的旱旱蔬菜轮作相比，进行水旱轮作后显著增加了细菌群落的多样性。好气土壤培养试验结果表明，随着淹水时间的推进，土壤反硝化效率逐渐提高，N2产生速率逐渐提高，且低氮土壤反硝化效率（99%）显著高于高氮土壤（60%）。设施菜地土壤淹水后，低氮土壤的硝化潜力显著高于高氮土壤。设施菜地土壤淹水后硝化作用主要由氨氧化细菌AOB主导；土壤NH4+-N含量增加是导致设施菜地土壤淹水后N2O排放增加的主要原因之一。

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