紫云英还田对稻田土壤氮素转化过程的影响及其微生物学机制

Chinese milk vetch (CMV) - rice cropping system possesses the functions of stabilizing rice production and reducing nitrogen losses from paddy field, while reducing fertilizer N input in successive rice season. These functions were verified both in the long-term and short-term field experiments. Many researches focused on the effects of incorporated CMV on rice yield formation, soil biological characteristics, nitrogen use efficiency and fertilizer N substitution, has attempted to uncover the mechanism in CMV-rice cropping system. However, few studies have focused on the soil N turnover effects after the incorporation of CMV residue. The experimental materials obtained from different rice cropping systems in the long-term site will be applied for the soil incubation experiments in this project. The 15N tracer technique combined with numerical analysis model will be employed to determine the soil N transformation rates, such as gross N mineralization, gross N nitrification, and the related microflora in rice different growth stages. The aim is to reveal the incorporated CMV effects on the soil N supply and N retention capacities, related microbial mechanism. The results will help us to understand the mechanism of the functions in CMV-rice cropping system, and predict the changes of soil N supply capacity in the long-term. The results also provide theoretical basis and technical guidance for the reasonable fertilization schemes, and ultimately reduce the fertilizer N input, the related N losses from the paddy field.

众多研究表明，长期和短期紫云英-水稻轮作系统稻季均具有减氮稳产减排这一功能。已有大量研究从产量形成过程，土壤生物学特性，氮肥利用效率，养分替代等方面尝试剖析了紫云英-水稻轮作系统减氮稳产或者减排的内在机制。而鲜有研究关注紫云英还田对稻田土壤氮素循环过程的影响及其反馈效应。本项目以太湖流域水稻轮作制度调整长期定位试验基地土壤为研究对象，采用15N示踪技术结合数值分析模型测定紫云英还田后水稻不同生育期土壤氮素矿化、硝化等初级转化速率，揭示紫云英还田对稻田土壤供氮和保氮的影响机制，并揭示其内在的微生物学机制，结果将有助于理解紫云英-水稻轮作系统减氮稳产减排的内在机制，也可预测持续紫云英-水稻轮作下土壤供氮能力的变化，进而为制定合理施肥措施、最终减少氮输入及相关的氮素损失提供理论依据和技术指导。

长期和短期紫云英-水稻轮作系统稻季均具有减氮稳产减排这一功能。然而紫云英还田对稻田土壤氮素转化过程的影响及其反馈效应尚不清楚。本项目以太湖流域水稻轮作制度调整长期定位试验土壤为研究对象，采用室内培养和田间试验方法，分析了水稻关键生育期土壤的供氮过程，揭示了紫云英还田对稻田土壤供氮和保氮能力的影响，并解析了其微生物学机制。研究结果表明：1）紫云英还田后土壤供氮能力随水稻生长期的增加而持续减弱，但仍能保证了水稻苗期和分蘖期的土壤供氮能力，满足了水稻苗期和分蘖期对氮素的需求；2）紫云英还田后土壤微生物群落存在明显的演替，长期紫云英还田减少了催化硝化作用第二步骤的相关菌群，从而削弱了稻田土壤的硝化过程及其硝化速率，增强了硝酸盐异养反硝化途径相关菌群，从而提高了水稻收获后土壤的保氮能力；3）紫云英还田后结合减少70%氮肥用量，可以保证水稻土供氮能力及水稻氮素吸收的同时，提高了氮肥利用效率，而且极大限度的减少了稻田的氮径流损失。在河网地区的稻田生态系统应用中，凸显了紫云英还田在可持续集约化战略中重要性。