Subjects: Agriculture, Forestry,Livestock & Aquatic Products Science >> Basic Disciplines of Agriculture submitted time 2017-11-08 Cooperative journals: 《中国生态农业学报》
Abstract：如何在保证作物高产的前提下, 提高氮肥利用率、减少氮肥损失及其对环境的影响已经成为一个世界性研究课题。硝态氮淋洗是旱地土壤氮素损失去向的重要途径之一, 是导致区域性地下水硝酸盐污染的重要原因, 已成为全球集约农区重大农业和生态环境问题。明确不同农作系统土壤硝态氮的产生、淋洗过程及影响因素, 并进一步提出阻控措施, 具有重要的农学和环境意义。在这一方面国内外学者已经开展了长期、大量的研究, 并积累了丰富的资料。本文综述了旱地土壤硝化作用的微生物驱动过程, 比较了当前最为常用的田间原位监测硝态氮淋洗方法的优缺点, 分析了影响硝态氮累积和淋洗的各种因素, 总结了相应的调控措施, 并对今后的研究工作进行展望: 加强旱地土壤硝化作用的关键微生物过程、机理以及相关驱动因子调控作用的研究, 有助于增加对土壤氮素循环的认识, 而这些认识是旱地农作系统进行氮素优化管理和制定硝态氮淋洗阻控技术的重要基础; 继续寻找和建立一种扰动更少、维护简单、样品污染更低、尤其适合长期监测的田间原位研究方法, 对于准确地揭示旱地土壤硝态氮的淋洗规律和实时通量尤为重要; 系统地开展不同旱地农作系统硝态氮淋洗的综合性研究, 阐明影响硝态氮累积和淋洗的主要因素, 并提出针对性的阻控措施, 更符合田间实际, 对于降低区域硝态氮淋洗风险意义重大。
Subjects: Geosciences >> Space Physics submitted time 2016-05-04
Abstract： The study of the ionosphere responses to Corotating Interaction Regions (CIRs) and Coronal Mass Ejections (CMEs) got much attentions in rencent years. With the comparison of different types of ionosphere response caused by different disturbance sources from solar activity and interplanetary solar wind, morphological changes and physical process of ionospheric storms can be understood more impressively and comprehensively. It provides a possibility to predict ionospheric disturbance states according to different solar wind conditions in advance as well. GPS-TEC data at a mid-latitude station (131 degrees E, 35 degrees N) are used to analyze the ionosphere response during geomagnetic disturbances induced by 109 CIRs and 45 CMEs over the period 2001 to 2009. Firstly, the TEC difference are determined to achieve the information of ionospheric positive or negative storms during the CIR and CME events. The definition of a ionospheric storms is relative TEC greater than or equal to 15% and persisting for more than 4 hours; Secondly, year dependence, seasonal dependence, time delay between ionospheric storms and geomagnetic storms, geomantic storm intensity dependence and time duration of ionospheric storms are analyzed in detail. Analysis results indicate that the types of ionospheric storms vary in different phases of a solar cycle. CIR-driven positive and positive-negative storms are more likely to occur in the declining phase of the solar cycle, while negative phase storms more in solar maximum and negative-positive storms mainly in solar minimum. CME-driven positive storms and negative storms mostly occur in solar maximum. There is no remarkable seasonal difference for the occurrence of different types of ionospheric storms except the positive-negative storms most likely to occur in summer. The time delays between geomagnetic disturbances and the start time of ionospheric storms are-6 to 6 hours in general, but CIR-driven ionopsheric storms involve in a wider range with a time delay of-12 to 24 hours and CME-driven storms is delayed from 6 to 6 hours. Moreover, for CIR-driven ionospheric storms, positive and negative storms mostly occur in main phase of magnetic storms, positive-negative storms mostly in initial and main phase, and negative-positive storms mainly in initial phase. For CME-driven storms, positive, negative and positive-negative storms basically occur in main phase. Our investigation also demonstrates certain correlation between the types of ionospheric storms and the AE maximum indices. Ionopsheric negative storms often occur in stronger geomagnetic activity, with the AE maximum intensity between 800 to 1200nT while positive-negative storms tend to occur with AE maximum intensity higher than 400 nT. Compared to CIR driven storms, AE maximum value during CME driven storms is higher. The duration of CIR-driven storms is longer (1 to 6 days) than that of CME-driven storms (1 to 4 days). The ionosphere response to interplanetary conditions contribute to the study the ionospheric disturbance. Statistical analysis of the ionosphere response to the CIR and CME in Mid-latitude regions indicate that there are some certain correlations among ionospheric changes, solar activities, interplanetary conditions and geomagnetic conditions. The ionospheric storms could be predicted more accurately and meticulously by distinguishing the different types of interplanetary conditions.
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